I have a 14 XTS, in which I just got new OEM shocks installed in the rear. Picked up the car today, the rear of the car still sits pretty low. I can hear the compressor kick on/off but the car isn’t raising up. No “Service Suspension” or any other error codes. Air spring bags seem to be full as well. Does the ESCM need to be reset or am I looking at something more serious? Thanks in advance for any replies/tips!
Air Suspension Problems.......
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Our vehicles do not have "air suspension" or "air ride". It's ELC - Electronic Level Control - which compensates for weight changes in the cargo area or rear seating. The suspension is regular or active (depending on suspension option) hydraulic struts/shocks and coil springs. The shocks (rear) incorporate air bladders for height control only. You need to inspect the rear suspension for loose electrical connections, correct air line hookup, and rear level sensor operation.
You are owed a new parts warranty inspection. It's NOT rocket science.
You are owed a new parts warranty inspection. It's NOT rocket science.
This is inaccurate information.
OP, The XTS does have rear air bag suspension. The shocks are not a component of the air suspension. They are just regular shocks.
The most common failure for your XTS is the air compressor. But it could also be the height sensor.
The rear on mine was low after the compressor was replaced. The dealer mechanic "used GDS to set the rear suspension trim height values to 470mm (maximum) to raise the rear of the vehicle body" quote. That fixed the lowrider look.
Ok I think we are confusing terminology here - shocks and struts get confused all the time.
The XTS has four STRUTS, one at each corner. These are the "Magneride" units and are simply dampers. Then there are two coil springs at the front, and two air springs in the back. If the OP had his struts replaced, that would not affect the air suspension in any way. However, he should be getting an alert if the rear isn't rising, because the compressor would keep running well past it's timeout threshold.
OP - is your compressor running for more than 60 seconds at startup? If so you have a problem with the air springs, air lines, or level sensors. If it's running long and the rear is not rising, that indicates either a spring or line leak. If it's not running long but the rear is still too low, then that's a calibration issue - the computer thinks the rear is level when it's not.
Sub, your response?
Sorry about your situation. Who replaced the shocks (dealership)?
Link to GM Direct: https://www.gmpartsdirect.com/auto-...ear-suspension-cat/shocks-and-components-scat
I have a 2014 (Luxury) as well. I have had my front struts replaced (dealership) but not my rear shocks. However, the front strut did cause my vehicle to list to one side. So much so, that we (dealership staff and I) thought it was a rear shock issue.
Link to GM Direct: https://www.gmpartsdirect.com/auto-...ear-suspension-cat/shocks-and-components-scat
I have a 2014 (Luxury) as well. I have had my front struts replaced (dealership) but not my rear shocks. However, the front strut did cause my vehicle to list to one side. So much so, that we (dealership staff and I) thought it was a rear shock issue.
If I'm off-base on the suspension type and components then the GM/Cadillac service manuals should be consulted. Not being a 2014 XTS owner, I was using generic Cadillac Level Control suspension knowledge.
From parts sources it's worthy of note that the 2014 XTS use front struts and rear shocks, with the type depending on whether the suspension is active or passive. There IS an "air spring" listed for the rear.
GM confuses terminology all the time too. Plus we are dealing with a few differences in trim levels (i.e. less common trims do not have Magneride and the air suspension). However, the rear Magneride dampers on the XTS act as torsional support members and weight support members which makes them struts and not shocks. Shocks cannot support vehicle weight and cannot act as torsional members. If you remove Magneride from the equation then you only have minor torsional support so I think one could be forgiven for calling them shocks.
This is of course an irrelevant tangent as it doesn't make a difference in relation to the OP's issue.
Just so everyone's on the same page. . .
Front & Rear Suspension General Description GNA (Non HiPerStrut)
General Description (GNB)
HiPerStrut Front Suspension:
The front suspension has two primary purposes:
Isolate the driver from irregularities in the road surface.
Define the ride and handling characteristics of the vehicle.
The front suspension absorbs the impact of the tires travelling over irregular road surfaces and dissipates this energy throughout the suspension system. This process isolates the vehicle occupants from the road surface. The rate at which the suspension dissipates the energy and the amount of energy absorbed by the suspension system defines the vehicles ride characteristics. The Electronic Suspension Control system controls the XTS ride characteristics. The Electronic Suspension Control system individually controls the damping force of each of the four shock absorbers. The suspension system must allow for the vertical movement of the tire and wheel assembly as the vehicle travels over irregular road surfaces while maintaining the horizontal relationship of the tire to the road.
This requires the Steering Knuckle be suspended between a Lower Control Arm via a Yoke Assembly to the Strut Assembly. The Lower Control Arm outermost point is attached to the Yoke Assembly via the King Pin Bushing to the Steering Knuckle. The innermost end of the Control Arm attaches at two points to the vehicle frame through semi-rigid bushings. The upper portion of the Steering Knuckle is attached to the Yoke Assembly via a Ball Stud. The Yoke Assembly connects to the Strut Assembly and vehicle body via an Upper Bushing. The Steering Knuckle travels up and down independent of the vehicle body structure and frame.
The up-and-down motion of the Steering Knuckle as the vehicle travels over bumps is absorbed predominantly by the Coil Spring. This spring is held under tension over the Strut Assembly. A strut is used in conjunction with this system in order to dampen the oscillations of the Coil Spring. The oil-filled strut has a moveable shaft connected to a piston inside the strut. Valves inside the shock absorber offer resistance to oil flow and inhibiting rapid movement of the piston and shaft. Each end of the shock absorber is connected in such a fashion to utilize this recoil action of a spring alone. Each end of the strut is designed as the connection point of the suspension system to the vehicle and acts as the Coil Spring seat. This allows the strut to use the dampening action, reducing the recoil of a spring alone. The lower control arm pivots at the vehicle frame vertically. A ball joint allows the Steering Knuckle to maintain the perpendicular relationship to the road surface.
Front suspensions systems use a stabilizer bar. The stabilizer bar connects between the left and right strut assemblies through the stabilizer link and stabilizer shaft insulators. This bar controls the amount of independent movement of the suspension when the vehicle is turning. Limiting the independent movement defines the vehicles handling characteristics when turning.
The advantage of the HiPerStrut front suspension (GNB) over the McPherson-type wheel suspension is less spindle length, providing:
Reduced smooth road shake
Less torque steer
Increased cornering power, no camber loss during cornering
Robustness against wheel imbalance
The HiPerStrut design provides improved ride and handling performance with a premium steering feel.
The design enables bigger wheels.
The design allows camber adjustment with screws on the Steering Knuckle upper ball stud.
Rear Suspension Description and Operation
The XTS Rear Suspension system is the independent link type. Rear suspension adjustment uses adjustable toe links and lower control arms. The rear air springs are positioned between the body and lower control arm. The rear suspension consists of two shock absorbers attached to the knuckle and the reinforced body areas.
The Rear Suspension system:
Maintains the relationship of the rear axle to the body
Controls the torque reaction on acceleration and braking
The Rear Suspension system consists of the following components:
Support assembly
Air springs
Stabilizer shaft, insulators, and stabilizer links
Toe links
Upper control arms
Lower control arms
Trailing arms
Knuckles
Wheel bearing/hub
Shock absorbers
Front & Rear Suspension General Description GNA (Non HiPerStrut)
General Description (GNB)
HiPerStrut Front Suspension:
The front suspension has two primary purposes:
Isolate the driver from irregularities in the road surface.
Define the ride and handling characteristics of the vehicle.
The front suspension absorbs the impact of the tires travelling over irregular road surfaces and dissipates this energy throughout the suspension system. This process isolates the vehicle occupants from the road surface. The rate at which the suspension dissipates the energy and the amount of energy absorbed by the suspension system defines the vehicles ride characteristics. The Electronic Suspension Control system controls the XTS ride characteristics. The Electronic Suspension Control system individually controls the damping force of each of the four shock absorbers. The suspension system must allow for the vertical movement of the tire and wheel assembly as the vehicle travels over irregular road surfaces while maintaining the horizontal relationship of the tire to the road.
This requires the Steering Knuckle be suspended between a Lower Control Arm via a Yoke Assembly to the Strut Assembly. The Lower Control Arm outermost point is attached to the Yoke Assembly via the King Pin Bushing to the Steering Knuckle. The innermost end of the Control Arm attaches at two points to the vehicle frame through semi-rigid bushings. The upper portion of the Steering Knuckle is attached to the Yoke Assembly via a Ball Stud. The Yoke Assembly connects to the Strut Assembly and vehicle body via an Upper Bushing. The Steering Knuckle travels up and down independent of the vehicle body structure and frame.
The up-and-down motion of the Steering Knuckle as the vehicle travels over bumps is absorbed predominantly by the Coil Spring. This spring is held under tension over the Strut Assembly. A strut is used in conjunction with this system in order to dampen the oscillations of the Coil Spring. The oil-filled strut has a moveable shaft connected to a piston inside the strut. Valves inside the shock absorber offer resistance to oil flow and inhibiting rapid movement of the piston and shaft. Each end of the shock absorber is connected in such a fashion to utilize this recoil action of a spring alone. Each end of the strut is designed as the connection point of the suspension system to the vehicle and acts as the Coil Spring seat. This allows the strut to use the dampening action, reducing the recoil of a spring alone. The lower control arm pivots at the vehicle frame vertically. A ball joint allows the Steering Knuckle to maintain the perpendicular relationship to the road surface.
Front suspensions systems use a stabilizer bar. The stabilizer bar connects between the left and right strut assemblies through the stabilizer link and stabilizer shaft insulators. This bar controls the amount of independent movement of the suspension when the vehicle is turning. Limiting the independent movement defines the vehicles handling characteristics when turning.
The advantage of the HiPerStrut front suspension (GNB) over the McPherson-type wheel suspension is less spindle length, providing:
Reduced smooth road shake
Less torque steer
Increased cornering power, no camber loss during cornering
Robustness against wheel imbalance
The HiPerStrut design provides improved ride and handling performance with a premium steering feel.
The design enables bigger wheels.
The design allows camber adjustment with screws on the Steering Knuckle upper ball stud.
Rear Suspension Description and Operation
The XTS Rear Suspension system is the independent link type. Rear suspension adjustment uses adjustable toe links and lower control arms. The rear air springs are positioned between the body and lower control arm. The rear suspension consists of two shock absorbers attached to the knuckle and the reinforced body areas.
The Rear Suspension system:
Maintains the relationship of the rear axle to the body
Controls the torque reaction on acceleration and braking
The Rear Suspension system consists of the following components:
Support assembly
Air springs
Stabilizer shaft, insulators, and stabilizer links
Toe links
Upper control arms
Lower control arms
Trailing arms
Knuckles
Wheel bearing/hub
Shock absorbers
But wait, there's more!
Air Suspension Description and Operation
Air Suspension
The purpose of the Air Suspension System is the following for the rear suspension under loaded and unloaded conditions:
The Air Suspension System must have a voltage supply of at least 12.6V to operate properly.
The Air Suspension System will maintain the rear (side) height within four mm (0.15 in) in all loading conditions and the leveling function will deactivate if the vehicle is overloaded. The side-to-side height variation is maintained within 8 mm (0.31 in). When the ignition is turned OFF, the Electronic Suspension Control Module (ESCM) remains active for between 30 minutes and 2 1/2 hours. The system will exhaust pressure within 30 minutes after the ignition is turned off, to lower the vehicle after unloading. In a temperature-controlled environment, the leakage of the complete load leveling system will not result in more than 1.four mm (0.05 in) drop of rear suspension height at GVWR during a 2four hour period. If the outdoor temperature drops from +20°C (+68°F) to −5°C (+23°F), the rear height may drop as much as 25 mm (1 in). However, the Air Suspension System should return to the specified height during the next ignition cycle.
Air Suspension Compressor Assembly
The Air Suspension Compressor Assembly houses the DC motor/air compressor, an Exhaust Valve Solenoid, and two Air Spring Isolation Valve Solenoids. The ESCM sends a voltage signal to each height sensor and measures the inductance of the return signal to determine if one or both air springs need to be inflated or deflated. Before the compressor starts, the exhaust valve is activated, providing compressor head pressure relief. Next, the Compressor Relay activates to start the compressor. When the trim height is achieved the relay is de-energized. To prevent the compressor from overheating, the compressor operates on a duty cycle. If the compressor is requested to operate continually, the compressor duty cycle is limited to 300 seconds at maximum output for the first cycle. After this time, the compressor automatically switches off for at least 92 seconds. After that, the compressor activates for 16 seconds and de-activates for 92 seconds. This 16/92 second duty cycle continues until the compressor can remain off for more than 92 seconds.
The Air Suspension Compressor Assembly has three different operating modes:
Air Suspension Sensors
The Air Suspension Sensor Arm attaches to an armature that rotates within a coil. The inductance of the coil, (not the resistance) changes depending on the position of the armature in the coil. The Air Suspension Module determines the angle of the sensor arm by sending an inductive voltage through the coil and measures the response time. The sensors must be calibrated to the correct side-to-side (D) height.
Rear Air Springs
The air springs are mounted in the frame in the same location where the coil spring is mounted for a vehicle without air suspension. Support pieces are attached to the axle for the air springs.
Electronic Suspension Control Description and Operation
Electronic Suspension Control Description
The Electronic Suspension Control (ESC) system independently controls each of the four shock absorbers to control the vehicle ride characteristics. The ESC system is capable of making these changes within milliseconds. The ESC system consists of the following major components:
Electronic Suspension Control Module
The Electronic Suspension Control (ESC) module provides electronic control logic and output drive for each shock absorber. The ESC module makes decisions due to road and driving conditions based on various inputs. The ESC module receives input information by sensors directly connected to the ESC module or by other systems through the serial data line and uses these inputs to independently control the shock absorbers at each corner.
Electronic Suspension Control Position Sensors
The Electronic Suspension Control (ESC) position sensors provide the ESC module with the body-to- wheel displacement input. The ESC module uses this and other inputs to control the stiffness of the shock absorbers. If any vehicle body or wheel motion is detected, the ESC module determines how soft or firm each shock absorber should be to provide the best ride. ESC position sensors mount at each corner of the vehicle between the control arm and the body/frame.
Electronic Suspension Control Shock Absorber or Strut
The Electronic Suspension Control (ESC) shock absorbers provide variable damping to resist suspension movement. The ESC shock absorber has the capability of providing multiple modes or values of damping forces, in both compression and rebound direction. The damping forces are modified utilizing electrical actuators located internally within the shock absorbers.
Electronic Suspension Control Operation
The Electronic Suspension Control (ESC) system uses the information from other systems in order to execute certain functions.
The ESC system does not have a malfunction indicator lamp, but instead uses the instrument panel cluster (IPC) for the display functions. When the ESC system detects a malfunction that sets a DTC, the ESC system sends a message on the serial data line directly or through the powertrain control module (PCM) to the IPC, which will display one of the following messages:
The SERVICE SUSPENSION SYSTEM or SERVICE RIDE CONTROL messages is displayed if the ESC system detects any malfunction that sets a DTC. The ESC system will send a message on the serial data line to the IPC to display this message.
The SPEED LIMITED message is only displayed if the ESC system detects a malfunction that sets a DTC and causes the ESC system to disable all four shock absorbers. The ESC system will send a message on the serial data line to the PCM indicating that all four shock absorbers were disabled. The PCM then sends a message to the IPC to display this message.
The ESC module has the ability to store DTCs as current or history codes. Most ESC system malfunctions will display a message in the IPC and set a DTC. The message will remain ON until the RESET button is pressed on the Driver Information Center (DIC). As long as the DTC is current, the message is displayed after every ignition cycle and the RESET button must be pressed to bypass the message.
The ESC system uses an ignition cycling diagnostic approach in order to reduce the occurrence of false or intermittent DTCs that do not affect the functionality of the ESC system. This allows for the fail-soft actions to be taken whenever a malfunction condition is current, but requires the malfunction to be current for a certain number of ignition cycles before the corresponding malfunction code and message will be stored or displayed.
If the ESC detects a malfunction, the ESC system defaults with a fail-soft action. A fail-soft action refers to any specific action the ESC system takes in order to compensate for a detected malfunction. A typical ESC fail-soft action would be if the ESC system detects a malfunction with a shock absorber.
Automatic Level Control
The Automatic Level Control (ALC) system maintains a desired rear suspension position under all types of loading conditions.
When the vehicle is unloaded, the rear suspension is at a desired position, which is monitored by the ESCM using the position sensor signal voltage inputs. As weight is added to the rear of the vehicle, the position sensor's signal voltage inputs change. When the ESCM detects a steady substantial change in the position sensor signal voltages for at least 10 seconds, it responds by commanding the compressor relay ON, which activates the compressor causing the air pressure in the air spring to inflate. This inflation raises the rear of the vehicle to regain the desired suspension position. When weight is removed from the vehicle, the ESCM responds by commanding the exhaust valve ON causing the air pressure in the air spring to deflate. This deflation lowers the vehicle to regain the desired suspension position.
The compressor is a positive displacement piston air pump driven by a 12-volt DC permanent magnet motor. The compressor draws filtered air through an intake line attached to an under body rail. The compressed air is sent through a dryer containing a moisture-absorbing chemical that dries the compressed air before it is sent to the air springs. Each time the compressor activates, the ESCM commands the exhaust valve ON for 1.5 seconds to release air from the compression chamber in the compressor’s cylinder head ensuring low motor current draw upon compressor activation. The ESCM also limits the amount of compressor run time to 180 seconds to protect the compressor components from thermal damage.
The ESCM has the ability to detect malfunctions within the ALC system. Any malfunctions detected will cause the DIC to display the SERVICE LEVELING SYSTEM message.
Front Suspension General Description (GNB)
Hi-Per Strut Front Suspension:
The two primary purposes of the front suspension are to:
Isolate the driver from irregularities on the road surface.
Define the ride and handling characteristics of the vehicle.
The front suspension absorbs impacts of the tires travelling over irregular road surfaces and dissipates the impact energy throughout the suspension system. This isolates the occupants of the vehicle from the road surface. The rate at which the suspension dissipates the impact energy and the amount of energy that is absorbed defines the vehicle’s ride characteristics. Ride characteristics are controlled by the Electronic Suspension Control system. The Electronic Suspension Control system individually controls the damping force of each of the four shock absorbers. The suspension system must allow for the vertical movement of the tire and wheel assembly as the vehicle travels over irregular road surfaces while maintaining the tire's horizontal relationship to the road.
This requires that the steering knuckle be suspended between a lower control arm via the yoke assembly to the strut assembly. The lower control arm outermost point is attached to the yoke assembly and then through the king pin bushing to the steering knuckle. The innermost end of the control arm attached at 2 points to the vehicle frame through semi-rigid bushings. The upper portion of the steering knuckle attaches to the yoke assembly though a ball stud. The yoke assembly connects to the strut assembly and vehicle body though an upper bushing. The steering knuckle travels up and down independent of the vehicle body structure and frame.
The up-and-down motion of the steering knuckle as the vehicle travels over bumps is absorbed predominantly by the coil spring. This spring is retained under tension over the strut assembly. A strut is used in conjunction with this system in order to dampen out the oscillations of the coil spring. The strut is filled with oil and has a moveable shaft that connects to a piston inside the strut. Valves inside the shock absorber offer resistance to oil flow to prevent rapid movement of the piston and shaft. Each end of the shock absorber connects in such a way to use the recoil action of the spring. Each end of the strut is designed as the connection point of the suspension system to the vehicle and acts as the coil spring seat. This allows the strut to use the dampening action to reduce the recoil of just a spring. The Lower Control Arm is pivots at the vehicle frame vertically. The ball joint allows the steering knuckle to maintain the perpendicular relationship to the road surface.
Front suspensions systems utilize a stabilizer bar. The stabilizer bar connects between the left and right strut assemblies through the stabilizer link and stabilizer bar insulators. This bar controls the amount of independent movement of the suspension when the vehicle turns. Limiting the independent movement defines the vehicles handling characteristics on turns.
The advantage of the HiPerStrut front suspension (GNB) over the McPherson-type wheel suspension is less spindle length, which leads to:
Reduced smooth road shake
Less torque steer
Increased cornering power, no camber loss during cornering
Robustness against wheel imbalance
The HiPerStrut design provides improved ride and handling performance with a premium steering feel.
The design enables larger diameter wheels.
The design allows camber adjustment with screws on the steering knuckle upper ball stud.
Rear Suspension Description and Operation
The XTS Rear Suspension System is the independent link type. Rear suspension adjustment is achieved through adjustable toe links and lower control arms. The rear air springs are fixed between the body and Lower Control Arm. The rear suspension consists of two shock absorbers attached to the knuckle and the reinforced body areas.
The Rear Suspension System performs the following functions:
Maintains the relationship of the rear axle to the body
Controls the torque reaction on acceleration and braking
The suspension system consists of the following components:
Support assembly
Air springs
Stabilizer shaft, insulators and stabilizer links
Toe links
Upper control arms
Lower control arms
Trailing arms
Knuckles
Wheel bearing/hub
Shock absorbers
Air Suspension Description and Operation
Air Suspension
The purpose of the Air Suspension System is the following for the rear suspension under loaded and unloaded conditions:
- Keep the vehicle visually level
- Provide optimal headlight aiming
- Maintain optimal ride height
- Air Suspension Compressor assembly
- Air Suspension Sensors
- Rear Air Springs
The Air Suspension System must have a voltage supply of at least 12.6V to operate properly.
The Air Suspension System will maintain the rear (side) height within four mm (0.15 in) in all loading conditions and the leveling function will deactivate if the vehicle is overloaded. The side-to-side height variation is maintained within 8 mm (0.31 in). When the ignition is turned OFF, the Electronic Suspension Control Module (ESCM) remains active for between 30 minutes and 2 1/2 hours. The system will exhaust pressure within 30 minutes after the ignition is turned off, to lower the vehicle after unloading. In a temperature-controlled environment, the leakage of the complete load leveling system will not result in more than 1.four mm (0.05 in) drop of rear suspension height at GVWR during a 2four hour period. If the outdoor temperature drops from +20°C (+68°F) to −5°C (+23°F), the rear height may drop as much as 25 mm (1 in). However, the Air Suspension System should return to the specified height during the next ignition cycle.
Air Suspension Compressor Assembly
The Air Suspension Compressor Assembly houses the DC motor/air compressor, an Exhaust Valve Solenoid, and two Air Spring Isolation Valve Solenoids. The ESCM sends a voltage signal to each height sensor and measures the inductance of the return signal to determine if one or both air springs need to be inflated or deflated. Before the compressor starts, the exhaust valve is activated, providing compressor head pressure relief. Next, the Compressor Relay activates to start the compressor. When the trim height is achieved the relay is de-energized. To prevent the compressor from overheating, the compressor operates on a duty cycle. If the compressor is requested to operate continually, the compressor duty cycle is limited to 300 seconds at maximum output for the first cycle. After this time, the compressor automatically switches off for at least 92 seconds. After that, the compressor activates for 16 seconds and de-activates for 92 seconds. This 16/92 second duty cycle continues until the compressor can remain off for more than 92 seconds.
The Air Suspension Compressor Assembly has three different operating modes:
- Single Value Mode inflates and deflates the two air springs independently. This is the normal operating mode of the system. The system will enter Mean Value Mode when the sensor output indicates the difference between the height on each side is greater than 15.5 mm.
- In Mean Value Mode, the ESCM averages the signals from each height sensor to maintain an average trim height. If the measurement differential between the two (side) heights reaches approximately four mm, the system will enter Lock Mode and no leveling occurs. This compensates for uneven loading of the vehicle or if the vehicle is parked on an uneven surface. The Air Suspension Compressor Assembly has a wheel change (jack) control that prevents the air springs from deflating completely. If the ESCM detects that one or both of the rear wheels has a side height measurement of more than 235 mm, the system enters Lock Mode and suspends leveling functions until the suspension is moved toward the frame.
Air Suspension Sensors
The Air Suspension Sensor Arm attaches to an armature that rotates within a coil. The inductance of the coil, (not the resistance) changes depending on the position of the armature in the coil. The Air Suspension Module determines the angle of the sensor arm by sending an inductive voltage through the coil and measures the response time. The sensors must be calibrated to the correct side-to-side (D) height.
Rear Air Springs
The air springs are mounted in the frame in the same location where the coil spring is mounted for a vehicle without air suspension. Support pieces are attached to the axle for the air springs.
Electronic Suspension Control Description and Operation
Electronic Suspension Control Description
The Electronic Suspension Control (ESC) system independently controls each of the four shock absorbers to control the vehicle ride characteristics. The ESC system is capable of making these changes within milliseconds. The ESC system consists of the following major components:
- The Electronic Suspension Control (ESC) module
- The front/rear Position Sensors
- The front/rear adjustable Shock Absorbers
- The shock absorber Electrical Actuators, which are integrated within the shock absorbers
- The rear Air Springs
- Vehicle speed
- Steering wheel position
- Body-to-wheel displacement
Electronic Suspension Control Module
The Electronic Suspension Control (ESC) module provides electronic control logic and output drive for each shock absorber. The ESC module makes decisions due to road and driving conditions based on various inputs. The ESC module receives input information by sensors directly connected to the ESC module or by other systems through the serial data line and uses these inputs to independently control the shock absorbers at each corner.
Electronic Suspension Control Position Sensors
The Electronic Suspension Control (ESC) position sensors provide the ESC module with the body-to- wheel displacement input. The ESC module uses this and other inputs to control the stiffness of the shock absorbers. If any vehicle body or wheel motion is detected, the ESC module determines how soft or firm each shock absorber should be to provide the best ride. ESC position sensors mount at each corner of the vehicle between the control arm and the body/frame.
Electronic Suspension Control Shock Absorber or Strut
The Electronic Suspension Control (ESC) shock absorbers provide variable damping to resist suspension movement. The ESC shock absorber has the capability of providing multiple modes or values of damping forces, in both compression and rebound direction. The damping forces are modified utilizing electrical actuators located internally within the shock absorbers.
Electronic Suspension Control Operation
The Electronic Suspension Control (ESC) system uses the information from other systems in order to execute certain functions.
The ESC system does not have a malfunction indicator lamp, but instead uses the instrument panel cluster (IPC) for the display functions. When the ESC system detects a malfunction that sets a DTC, the ESC system sends a message on the serial data line directly or through the powertrain control module (PCM) to the IPC, which will display one of the following messages:
- SHOCKS INOPERATIVE
- SERVICE SUSPENSION SYSTEM or SERVICE RIDE CONTROL
- SPEED LIMITED
The SERVICE SUSPENSION SYSTEM or SERVICE RIDE CONTROL messages is displayed if the ESC system detects any malfunction that sets a DTC. The ESC system will send a message on the serial data line to the IPC to display this message.
The SPEED LIMITED message is only displayed if the ESC system detects a malfunction that sets a DTC and causes the ESC system to disable all four shock absorbers. The ESC system will send a message on the serial data line to the PCM indicating that all four shock absorbers were disabled. The PCM then sends a message to the IPC to display this message.
The ESC module has the ability to store DTCs as current or history codes. Most ESC system malfunctions will display a message in the IPC and set a DTC. The message will remain ON until the RESET button is pressed on the Driver Information Center (DIC). As long as the DTC is current, the message is displayed after every ignition cycle and the RESET button must be pressed to bypass the message.
The ESC system uses an ignition cycling diagnostic approach in order to reduce the occurrence of false or intermittent DTCs that do not affect the functionality of the ESC system. This allows for the fail-soft actions to be taken whenever a malfunction condition is current, but requires the malfunction to be current for a certain number of ignition cycles before the corresponding malfunction code and message will be stored or displayed.
If the ESC detects a malfunction, the ESC system defaults with a fail-soft action. A fail-soft action refers to any specific action the ESC system takes in order to compensate for a detected malfunction. A typical ESC fail-soft action would be if the ESC system detects a malfunction with a shock absorber.
Automatic Level Control
The Automatic Level Control (ALC) system maintains a desired rear suspension position under all types of loading conditions.
When the vehicle is unloaded, the rear suspension is at a desired position, which is monitored by the ESCM using the position sensor signal voltage inputs. As weight is added to the rear of the vehicle, the position sensor's signal voltage inputs change. When the ESCM detects a steady substantial change in the position sensor signal voltages for at least 10 seconds, it responds by commanding the compressor relay ON, which activates the compressor causing the air pressure in the air spring to inflate. This inflation raises the rear of the vehicle to regain the desired suspension position. When weight is removed from the vehicle, the ESCM responds by commanding the exhaust valve ON causing the air pressure in the air spring to deflate. This deflation lowers the vehicle to regain the desired suspension position.
The compressor is a positive displacement piston air pump driven by a 12-volt DC permanent magnet motor. The compressor draws filtered air through an intake line attached to an under body rail. The compressed air is sent through a dryer containing a moisture-absorbing chemical that dries the compressed air before it is sent to the air springs. Each time the compressor activates, the ESCM commands the exhaust valve ON for 1.5 seconds to release air from the compression chamber in the compressor’s cylinder head ensuring low motor current draw upon compressor activation. The ESCM also limits the amount of compressor run time to 180 seconds to protect the compressor components from thermal damage.
The ESCM has the ability to detect malfunctions within the ALC system. Any malfunctions detected will cause the DIC to display the SERVICE LEVELING SYSTEM message.
Front Suspension General Description (GNB)
Hi-Per Strut Front Suspension:
The two primary purposes of the front suspension are to:
Isolate the driver from irregularities on the road surface.
Define the ride and handling characteristics of the vehicle.
The front suspension absorbs impacts of the tires travelling over irregular road surfaces and dissipates the impact energy throughout the suspension system. This isolates the occupants of the vehicle from the road surface. The rate at which the suspension dissipates the impact energy and the amount of energy that is absorbed defines the vehicle’s ride characteristics. Ride characteristics are controlled by the Electronic Suspension Control system. The Electronic Suspension Control system individually controls the damping force of each of the four shock absorbers. The suspension system must allow for the vertical movement of the tire and wheel assembly as the vehicle travels over irregular road surfaces while maintaining the tire's horizontal relationship to the road.
This requires that the steering knuckle be suspended between a lower control arm via the yoke assembly to the strut assembly. The lower control arm outermost point is attached to the yoke assembly and then through the king pin bushing to the steering knuckle. The innermost end of the control arm attached at 2 points to the vehicle frame through semi-rigid bushings. The upper portion of the steering knuckle attaches to the yoke assembly though a ball stud. The yoke assembly connects to the strut assembly and vehicle body though an upper bushing. The steering knuckle travels up and down independent of the vehicle body structure and frame.
The up-and-down motion of the steering knuckle as the vehicle travels over bumps is absorbed predominantly by the coil spring. This spring is retained under tension over the strut assembly. A strut is used in conjunction with this system in order to dampen out the oscillations of the coil spring. The strut is filled with oil and has a moveable shaft that connects to a piston inside the strut. Valves inside the shock absorber offer resistance to oil flow to prevent rapid movement of the piston and shaft. Each end of the shock absorber connects in such a way to use the recoil action of the spring. Each end of the strut is designed as the connection point of the suspension system to the vehicle and acts as the coil spring seat. This allows the strut to use the dampening action to reduce the recoil of just a spring. The Lower Control Arm is pivots at the vehicle frame vertically. The ball joint allows the steering knuckle to maintain the perpendicular relationship to the road surface.
Front suspensions systems utilize a stabilizer bar. The stabilizer bar connects between the left and right strut assemblies through the stabilizer link and stabilizer bar insulators. This bar controls the amount of independent movement of the suspension when the vehicle turns. Limiting the independent movement defines the vehicles handling characteristics on turns.
The advantage of the HiPerStrut front suspension (GNB) over the McPherson-type wheel suspension is less spindle length, which leads to:
Reduced smooth road shake
Less torque steer
Increased cornering power, no camber loss during cornering
Robustness against wheel imbalance
The HiPerStrut design provides improved ride and handling performance with a premium steering feel.
The design enables larger diameter wheels.
The design allows camber adjustment with screws on the steering knuckle upper ball stud.
Rear Suspension Description and Operation
The XTS Rear Suspension System is the independent link type. Rear suspension adjustment is achieved through adjustable toe links and lower control arms. The rear air springs are fixed between the body and Lower Control Arm. The rear suspension consists of two shock absorbers attached to the knuckle and the reinforced body areas.
The Rear Suspension System performs the following functions:
Maintains the relationship of the rear axle to the body
Controls the torque reaction on acceleration and braking
The suspension system consists of the following components:
Support assembly
Air springs
Stabilizer shaft, insulators and stabilizer links
Toe links
Upper control arms
Lower control arms
Trailing arms
Knuckles
Wheel bearing/hub
Shock absorbers
Respectively sir, this is not all the case. Magnaride does not support weight, it changes the stiffness of dampening. The rear dampeners on a XTS are not a support member in any way, shape or form. One could remove the rear dampeners and the vehicle could still be driven around at ride height without a problem (other then no dampening). It is absolutely a shock.
A strut on the other hand is a structural support member of a suspension (like the the front of XTS). If a strut is removed, the suspension folds in on itself and the vehicle is undrivable.
I want to make very clear this is one of those terminology arguments that is really a moot point, we are discussing a pointless technicality.
That said, here's a generic pic of what the rear dampers in an XTS look like:
Note the upper mount - not a pivot. That makes them torsional support members. You COULD try to drive the XTS without the rear dampers in place, but drive in a spirited fashion and you are likely to bend the lower control arm mounts. Furthermore, Magneride IS used to support vehicle weight as both compression and rebound are independently variable on the XTS struts (the Magneride system in the XTS can increase compression to the point where it will LIFT a corner of the car in a turn or maneuver).
Again, I would allow that if you remove EITHER of the two above conditions, you could reasonably argue that we are talking about shocks - because the difference would be so minor as to be inconsequential.
This is a Magneride shock from an Escalade:
Note the pivots at both mounting locations. This makes the damper unable to act as a support member in any way. In addition, compression and rebound are mechanically linked in this unit and cannot be actuated separately.
So yeah this is kind of a silly argument because we're talking about technicalities. But i'm an engineer so it's what I do.
So, I've been following the discussion with interest and educating myself on XTS suspension and General Motors Magnetic Ride Control Technology. Magneride appears to be dampening, or literally electrically variable shocks controlled in real-time .
I don't have MagneRide or Load Leveling(?) and I haven't been or seen under my '18 Lux but it has:
6FG - COMPONENT FRT LH COMPUTER SEL SUSP
7FG - COMPONENT FRT RH COMPUTER SEL SUSP
8FB - COMPONENT RR LH COMPUTER SEL SUSP (8FB)
9FB - COMPONENT RR RH COMPUTER SEL SUSP (9FB)
GNB - SUSPENSION FRONT PERFORMANCE
GNE - SUSPENSION, REAR H ARM
What do I have? Rear Air Springs/struts? Compressor? Standard front struts?
I don't have MagneRide or Load Leveling(?) and I haven't been or seen under my '18 Lux but it has:
6FG - COMPONENT FRT LH COMPUTER SEL SUSP
7FG - COMPONENT FRT RH COMPUTER SEL SUSP
8FB - COMPONENT RR LH COMPUTER SEL SUSP (8FB)
9FB - COMPONENT RR RH COMPUTER SEL SUSP (9FB)
GNB - SUSPENSION FRONT PERFORMANCE
GNE - SUSPENSION, REAR H ARM
What do I have? Rear Air Springs/struts? Compressor? Standard front struts?
I have a lifetime of automotive experience and know the XTS suspension well. Furthermore, I have extensive suspension experience that goes well beyond the automotive world. I could completely rebuild the XTS dampers on my workbench in my shop...and fully intend to tear one of mine open when one dies to see if the collar is easily fixable. What i've stated here is verifiably true, just look up the definitions of "strut" and "shock" for starters.
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