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P 0171 and P 0174 ?

4K views 19 replies 11 participants last post by  nwjones18 
#1 ·
I have torqued my intake bolts with locktite, and replaced,
the injector o rings twice, does this indicate,
i may need 02 sensor replacement ?
Thanks,
Happy Motoring :cool2::banghead::cool2:
 
#2 ·
Re: PO171 and PO174 ?

I too am lucky enough to have both of these codes on my car all the time.
They don't set CEL or MIL (whichever you want to call it) in my car but they show up in the tech 2.
My car had been in for service many times trying to get it fixed but nothing ever happened with it in the end.

DTC P0171 - Fuel Trim System Lean Bank 1
DTC P0174 - Fuel Trim System Lean Bank 2

Circuit/System Description

The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. A block of memory cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. The FT diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition.

If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.

Conditions for Running the DTC

The engine is in CL status.
The Fuel Trim Learn is enabled.
The engine coolant temperature (ECT) is between -38 and +150°C (-36.4 and +302°F).
The intake air temperature (IAT) is between -38 and +150°C (-36.4 and +302°F).
The manifold absolute pressure (MAP) is between 5-255 kPa (0.7-36.9 psi).
The vehicle speed is less than 134 km/h (83 mph).
The engine speed is between 400-6,000 RPM.
The mass air flow (MAF) is between 0.5-510 g/s.
The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
The fuel level is more than 10 percent.

Conditions for Setting the DTC

DTCs P0171, P0174 are Type B DTCs.
The long term FT weighted average value is more or less than a calibrated value.
The above condition is present for approximately 3 minutes after the Conditions for Running the DTC have been met.

Action Taken When the DTC Sets

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second ignition cycle the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. The control module illuminates the malfunction indicator lamp (MIL) when one of the following occur:
The control module detects the same fuel trim failure during 2 consecutive trips.
The control module detects any fuel trim failure during any subsequent trip if the conditions at the time of failure meet the following criteria:
The engine load is within 20 percent of the previous test that failed.
The engine speed is within 375 RPM of the previous test that failed.
The engine coolant temperature is in the same range of the previous test that failed.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC and related Freeze Frame data clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.


Circuit/System Verification

Important: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.

Verify that other DTCs are not set.
¤ If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (See: Diagnostic Trouble Code Descriptions) .
Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
¤ If the value does not vary from approximately 40 mV to approximately 900 mV, refer to DTC P0131, P0132, P0137, or P0138 (See: P0131) , DTC P0133, P0134, P0140, P1133, P2270, P2271, P2A00, or P2A01 (See: P0133) , DTC P0151, P0152, P0157, or P0158 (See: P0151) , or DTC P0153, P0154, P0160, P1153, P2272, P2273, P2A03, or P2A04 (See: P0153) .

Important: EVAP purge enablement may cause the FT to be momentarily outside the normal range.

The normal Short Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.
The Long Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.
Circuit/System Testing

DTC P0171 or P0174

Allow the engine to reach operating temperature. With the engine running, observe the affected Long Term FT parameter with a scan tool. The value should be less than approximately 24 percent with the engine running at operating temperature.

If the value is more than 24 percent, inspect for the following:

With the ignition ON and the engine OFF, observe the manifold absolute pressure (MAP) sensor parameter. The MAP sensor pressure should be within the range specified for your altitude.
¤ If the MAP sensor does not indicate the correct barometric pressure, refer to DTC P0106 (See: P0106) and DTC P0107 or P0108 (See: P0107) .
Vacuum hoses for splits, kinks, and improper connections
Insufficient fuel in the tank
A malfunctioning MAF-Refer to DTC P0068 or P0121 (See: P0068) or DTC P0101 or P1101 (See: P0101) .
Low fuel pressure
Fuel contamination
Malfunctioning fuel injectors
Missing, loose, or leaking exhaust components from the HO2S forward
Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
The air induction system and the air intake ducts for leaks or for a missing air filter element
A cracked or damaged EVAP canister
Evaporative canister purge lines plugged or obstructed
The crankcase ventilation system for leaks
The HO2S for improper installation and for electrical wires or connectors that may have contacted the exhaust system
The HO2S signal circuit open, shorted to ground, or shorted to the low reference circuit
The HO2S sensor 1 low signal circuit for an open circuit or high resistance
Malfunctioning engine components

Repair Instructions

Air Cleaner Assembly Replacement
Air Cleaner Element Replacement
Evaporative Emission Canister Replacement
Evaporative Emission Canister Purge Solenoid Valve Replacement
Evaporative Emission Hoses/Pipes Replacement - Chassis/Canister
Fuel Injector and Fuel Rail Replacement
Primary Fuel Level Sensor Replacement
Fuel System Cleaning
Fuel Tank Draining
Heated Oxygen Sensor Replacement - Bank 1 Sensor 1
Heated Oxygen Sensor Replacement - Bank 1 Sensor 2
Manifold Absolute Pressure Sensor Replacement
Throttle Body Assembly Replacement
Repair Verification

Important:
After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim values.
In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420 or P0430 and verify that DTC P0420 or P0430 runs and passes.
Install any components or connectors that have been removed or replaced during diagnosis.
Perform any adjustments, programming, or setup procedures that are required when a component or module is removed or replaced.
Turn ON the ignition, with the engine OFF.
Important: DO NOT clear codes with the engine running. DTCs may reset in the same ignition cycle.

Clear the DTCs.
Turn OFF the ignition for 60 seconds.
Start the engine.
Duplicate the Conditions for Running the DTC and use Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset.
 
#4 ·
Yup this ^
The dealers motto was as long as there is no MIL / CEL not to worry about it.
They blamed it on various things like too much ethanol in the fuel to intake gasket and loose manifold bolts but they either didn't want to follow the lengthy diagnostic steps above or they did them and still it wasn't resolved.
 
#6 ·
I tried cleaning my MAF with MAF cleaner twice and it persisted. Finally after reading a member on here's post about how the dealership swapped his MAF with a new car on the lot, I ordered a new MAF from Amazon ($70 bucks shipped).

CEL hasn't come up with that code since and I gained back 40km+ / tank again.

CEL has come back up, but I think it's a suspension code...
 
#7 ·
With lean codes on both banks I'd put O2 sensors way down to the bottom of the list for suspects. Could be an air leak anywhere after the MAF, a bad or contaminated MAF sensor, or a fuel delivery issue. If you have a scan tool capable of viewing live data you can narrow the list down pretty easily with fuel trim. Without that it is visual inspection and process of elimination. The most common issues I see with these codes are air leaks after the MAF and bad MAF's. But if you also have P1101 the PCM may need an update.
 
#9 ·
I have a 2005 Sts with N*, I'm looking to get advice on these codes as well. I feel like I have done almost everything (intake gaskets, torqued manifold bolts, replaced cracked vacuum hoses, cleaned MAF and throttle body, replaced fuel filter, update ECM). Is there anything I'm missing? I should probably just go ahead and get a new MAF sensor, unless someone points me in a different direction.

Any help would be greatly appreciated! Thanks!
 
#14 ·
I've had these codes myself, did everything you guys did and the codes persisted, in the end there was an air leak between the MAF and Airbox, it seems to be a weak spot from years of replacing filters. I used some Blue RTV that remains flexible and it has worked for 3 years now. You would think it shouldn't matter upstream of the MAF but it does when it is that close to it.
 
#16 ·
It appears to have worked! I popped in the new one, cleared the code, and took it for a nice aggressive test drive on the interstate :p. No more P0171 or P0174 for me. In hindsight I wouldn't have tried to clean the throttle body or MAF sensor because the time and effort greatly outweighs the small costs.
 
#17 ·
Give it a couple tanks of gas to make a full conclusion. I did the exact same thing and after 2 tanks of gas, the P1074 came back on. It also will come back on after clearing it every 500-600 or 1.5 tanks of gas. P0171 doesn't seem to show anymore though.

I have a k&n filter that I may replace with a paper filter as my next step. Then it's fuel filter. Then it's for sale hahaha.
 
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