P0174

DTC P0171, P0172, P0174, or P0175

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptors
DTC P0171
- Fuel Trim System Lean Bank 1

DTC P0172
- Fuel Trim System Rich Bank 1

DTC P0174
- Fuel Trim System Lean Bank 2

DTC P0175
- Fuel Trim System Rich 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. The ECM monitors the heated oxygen sensor (HO2S) signal voltage and adjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes the long and short term fuel trim (FT) values. The short term FT values change rapidly in response to the HO2S voltage signals. These changes fine tune the engine fueling. The long term FT makes coarse adjustments in order to maintain an optimum air/fuel ratio. The ideal FT values are around zero percent. A positive FT value indicates that the ECM is adding fuel in order to compensate for a lean condition. A negative FT value indicates that the ECM is reducing the amount of fuel in order to compensate for a rich condition.

Conditions for Running the DTC

* DTCs P0030, P0050, P0053, P0059, P0101, P0102, P0103, P0106, P0107, P0108, P0131, P0132, P0133, P0134, P0135, P0151, P0152, P0153, P0154, P0155, P0201-P0208, P0300, P0301-P0308, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P2227, P2228, P2229, P2230 are not set.
* The engine is in Closed Loop status.
* The Catalyst Monitor Intrusive Test, Post O2 Diagnosis Intrusive Test, Device Control, and EVAP Diagnosis "tank pull down" are Not Active.
* The engine coolant temperature (ECT) is between -40 and +150°C (-40 and +302°F).
* The intake air temperature (IAT) is between:

- Except L96, -7 and +150°C (+19 and +302°F).
- L96 -20 and +150°C (-4 and +302°F).

* The manifold absolute pressure (MAP) is between 10-255 kPa (1.45-37 psi).
* The engine speed is between 375-7,000 RPM.
* The mass air flow (MAF) is between 1-510 g/s.
* The barometric pressure (BARO) is greater than 70 kPa (10.2 psi).
* The fuel level is greater than 10 percent.
* This diagnostic runs continuously when the above conditions have been met.

Conditions for Setting the DTC

* The average long term FT weighted average value is greater 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

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0171, P0172, P0174, and P0175 are Type B DTCs.

Diagnostic Aids

* 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.
* The normal Short Term FT and Long Term FT parameters should be between +10 and -10 percent the optimum with the engine running at operating temperature.
* E85 compatible engine only - Over-estimation of the ethanol content will result in a rich shift of fuel trim values, and under-estimation will result in a lean shift of fuel trim values. A fuel trim DTC may set if the learned alcohol content, Fuel Alcohol Content parameter on the scan tool, is different than the measured alcohol content in the vehicle such that fuel trim values exceed failure threshold values. Refer to Fuel Composition Diagnosis (Fuel Composition Diagnosis).
* A fuel system delivery condition causes this DTC to set. Thoroughly inspect all items that cause a rich or a lean condition. Refer to Fuel System Diagnosis (Without FPCM) (Testing and Inspection)Fuel System Diagnosis (FPCM) (Component Tests and General Diagnostics).
* Any un-metered air into the engine causes this DTC to set. Thoroughly inspect all areas of the engine for vacuum leaks.
* A MAF sensor condition can cause this DTC without setting a MAF DTC. If there is a MAF sensor condition, the MAF sensor parameters will appear to be within range.
* Inspect the air filter for being the correct one for this application. Make sure that the engine oil fill cap is in place, and that it is tight. Verify that the engine oil dip stick is fully seated.

Reference Information
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Control Module References) for scan tool information

Circuit/System Verification

1. Engine running, observe the DTC information with a scan tool. Verify there are no HO2S DTCs set.

• If any DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).

2. Ignition ON, engine OFF, observe the Manifold Absolute Pressure (MAP) Sensor parameter. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure (Altitude Versus Barometric Pressure).

• If the MAP sensor pressure is not within the range specified for your altitude, refer to DTC P0106 (P0106).

3. With the engine idling, observe the Mass Air Flow (MAF) Sensor parameter. The MAF Sensor parameter should be within 2-6 g/s at idle.

• If not within the specified range, refer to DTC P0101 or P1101 (Without Heavy Duty L96) (Without Heavy Duty L96)DTC P0101 or P1101 (Heavy Duty L96) (Heavy Duty L96) or DTC P0102 or P0103 (Without Heavy Duty L96) (Without Heavy Duty L96)DTC P0102 or P0103 (Heavy Duty L96) (Heavy Duty L96).

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

4. Engine at normal operating temperature, observe the scan tool Long Term FT parameter. The reading should be between -19 to +19 percent.

• If not within the specified range, verify none of the following conditions exist:

P0171 or P0174
* Vacuum hoses for splits, kinks, and improper connections
* Insufficient fuel in the tank
* Low fuel pressure - Refer to Fuel System Diagnosis (Without FPCM) (Testing and Inspection)Fuel System Diagnosis (FPCM) (Component Tests and General Diagnostics).
* Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool))Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool)) or Fuel Composition Diagnosis (Fuel Composition Diagnosis).
* Malfunctioning fuel injectors - Refer to Fuel Injector Diagnosis (CH47976) (Testing and Inspection)Fuel Injector Diagnosis (J39021 or Scan Tool) (Testing and Inspection).
* Missing, restricted, or leaking exhaust components - Refer to Symptoms - Engine Exhaust (Symptoms - Engine Exhaust).
* 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 filter element
* A cracked EVAP canister
* Evaporative pipes obstructed or leaking
* The crankcase ventilation system for leaks - Refer to Crankcase Ventilation System Inspection/Diagnosis (Testing and Inspection).

P0172 or P0175
* The air intake duct for being collapsed or restricted
* The air filter for being dirty or restricted
* Objects blocking the throttle body
* Excessive fuel in the crankcase
* The evaporative emissions control system for improper operation
* Missing, restricted, or leaking exhaust components - Refer to Symptoms - Engine Exhaust (Symptoms - Engine Exhaust).
* Malfunctioning fuel injectors - Refer to Fuel Injector Diagnosis (CH47976) (Testing and Inspection)Fuel Injector Diagnosis (J39021 or Scan Tool) (Testing and Inspection).
* Fuel contamination - Refer to Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool))Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool) (Alcohol/Contaminants-in-Fuel Diagnosis (Special Tool)) for gasoline, or to Fuel Composition Diagnosis (Fuel Composition Diagnosis) for E85.

5. If all conditions test normal, test the engine for a mechanical condition. Refer to Symptoms - Engine Mechanical (Symptoms - Engine Mechanical).
6. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.