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Discussion Starter · #1 ·
My analog speedometer is 10mph faster than my digital display. When I stop the car it just sits on 10 when digital goes to 0. I have a 2015 ATS-4 premium. Thanks
600775
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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When you start the car up, does the needle do a full sweep from zero to full scale during the instrument panel initialization sequence or does it never zero itself? The analog gauges use stepper motors with a controller setup to indicate the commanded values and the stepper motor for the speedometer may be defective.

You can try totally removing power by disconnecting the negative battery cable for a couple of minutes to see if a reset will clear the fault. After doing so, you will need to let the ECM recalibrate the throttle plate motor/sensor. The procedure is in your owner's manual and it is simple and only takes a few minutes; it doesn't require opening the hood and is done while sitting in the driver's seat.

Failure to run the throttle plate calibration routine after power loss/battery replacement will often result in a check engine light being set a short time later. Even if you don't get a CEL after battery replacement, it can still result in sub-optimal idle quality and throttle response due to a mismatch between previously learned and actual throttle plate position.

Rodger
 

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2009 SRX V6 RWD, 2011 CTS Premium Coupe
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I have the same problem in my CTS, which has actual gauges. Everyone just patted me on the head. Hope the suggestions you got work.
 

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Discussion Starter · #4 ·
When you start the car up, does the needle do a full sweep from zero to full scale during the instrument panel initialization sequence or does it never zero itself? The analog gauges use stepper motors with a controller setup to indicate the commanded values and the stepper motor for the speedometer may be defective.

You can try totally removing power by disconnecting the negative battery cable for a couple of minutes to see if a reset will clear the fault. After doing so, you will need to let the ECM recalibrate the throttle plate motor/sensor. The procedure is in your owner's manual and it is simple and only takes a few minutes; it doesn't require opening the hood and is done while sitting in the driver's seat.

Failure to run the throttle plate calibration routine after power loss/battery replacement will often result in a check engine light being set a short time later. Even if you don't get a CEL after battery replacement, it can still result in sub-optimal idle quality and throttle response due to a mismatch between previously learned and actual throttle plate position.

Rodger
Hi there, so when the car is off it sits at 10. And when I start it up it does a full sweep from 10 to max and back to 10 never lower. It’s like stuck there or something.
 

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Discussion Starter · #5 ·
When you start the car up, does the needle do a full sweep from zero to full scale during the instrument panel initialization sequence or does it never zero itself? The analog gauges use stepper motors with a controller setup to indicate the commanded values and the stepper motor for the speedometer may be defective.

You can try totally removing power by disconnecting the negative battery cable for a couple of minutes to see if a reset will clear the fault. After doing so, you will need to let the ECM recalibrate the throttle plate motor/sensor. The procedure is in your owner's manual and it is simple and only takes a few minutes; it doesn't require opening the hood and is done while sitting in the driver's seat.

Failure to run the throttle plate calibration routine after power loss/battery replacement will often result in a check engine light being set a short time later. Even if you don't get a CEL after battery replacement, it can still result in sub-optimal idle quality and throttle response due to a mismatch between previously learned and actual throttle plate position.

Rodger
Is this an expensive fix you think? And dose it hurt if I drive around with it like this for a little while? Thank you.
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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Is this an expensive fix you think? And dose it hurt if I drive around with it like this for a little while? Thank you.
It won't hurt anything to drive with it that way unless you get a ticket for going too slow :)

This is probably going to be a dealer visit and it could be expensive because they will probably replace the instrument cluster as a complete unit and generally the cluster has to be programmed to the vehicle.

It would be an odd occurrence but I guess that the pointer could have mechanically slipped on the stepper motor shaft. You could try removing the cluster or the cover over it and see if you can carefully slip (hold the stepper motor shaft with a pair of needle nose pliers to keep it in position) or remove and re-install the pointer.

This was a fairly common supplier issue with the 2000 era HD pickup truck cluster and it was generally the temperature or oil pressure gauge resting above zero with power off but that issue was there from the original build instead of developing later in life.

Other than the inconvenience of having the indicator 10 MPH off, you can drive it that way for as long as you wish without it causing any additional damage. It is simply an indicator for the driver and does not provide data to any of the vehicle control systems.

Rodger
 

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2018 ATS Sedan 2.0 Turbo AWD (stablemates 2019 Corvette Stingray + 2010 LaCrosse CXS)
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Is this gonna drive the mileage up more than it should?
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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No impact upon registered/recorded mileage, from what he has described it is purely an issue with the analog indicator (pointer never returns to zero even with the ignition off).

My 2006 GMC Sierra 2500HD got a new cluster shortly after I took delivery because the coolant temperature gauge had the same issue with an offset from zero because of the stepper motor driving it. Stepper motors are pretty reliable but they are electro-mechanical devices so things can and do go wrong.

The stepper motor "knows" and reports back to its controller the exact rotational position of the shaft; the throttle plate is another part of the car controlled by a stepper motor but if that one develops an issue it isn't something that can be ignored. It is a key part of the "drive by wire" system and the accelerator pedal input is treated as a suggestion to the ECM as it determines how much power to actually request from the engine. In the ATS the result is subtle but the pattern of response to accelerator pedal input is slightly different in tour, sport, and snow/ice modes and very different when TC and/or StabiliTrak is managing the powertrain.

If my ATS developed this issue, I might not notice right away because with my HUD equipped vehicles almost never pay attention to the analog speedometer and why my only complaint about my 2018 Sierra Denali is that HUD wasn't available when I ordered it. Actually GM claimed it has a HUD but it consists of a flashing red light displayed on the windshield if the collision warning system gets upset.

Rodger
 

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2017 ATS Coupe 2.0T Luxury, formerly 2011 CTS Coupe Performance
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Highly technical point I'm going to hang Rodger up on.

Is it a stepper motor if it doesn't move in step-wise or piece-wise fashion? Doesn't the sweep action mean that it's technically a servo motor?

I have a small amount of scar tissue on this bit of nomenclature because as an engineering "intern" at TI, I was attached to a robotics/automation project. The machine in question used both stepper and servo motors of similar size/torque/current rating. I was asked to order some "stepper motors" to keep for replacement purposes. But the engineer meant "servo motors." So I dug up the drawings, located the steppers and ordered them up from our vendor.

When replacements were needed, it was servos, not steppers that we needed, but thanks to me and the engineer, we only had stepper motors. So the machine was down for a couple of extra days. Not really a big deal, but mildly embarrassing.
 

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TwiceHorn,

I am pretty sure that the ATS gauge still uses stepper instead of the more complex servo motors. The only one I have been inside was the problematic gauge cluster used in the early through mid 2000 era full size pickup/SUV platform and those used bipolar stepper motors with gear reduction for all of the instruments including the speedometer and tachometer. With gear reduction drive, the fairly coarse steps of the driving motor become much finer steps at the output shaft so the motion of the indicator needle appears very smooth.

This required smoothness can also be done electronically via micro-stepping which divides each major step into a larger number of micro steps. This requires a more complex driver setup for the motor. I haven't been inside newer GM clusters so I don't know whether they have gone with a micro stepper setup to replace the gear drive solution.

Servo motor setups are more expensive and the capabilities of it (i.e. very precise speed and torque control along with high accuracy real time feedback to the controller) aren't really needed for the readout in a vehicle.

Rodger
 
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