GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2005 🢒 L300/LW300 🢒 Brakes 🢒 Park Brake 🢒 DTC P0172 or P0175

Circuit 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 and Closed Loop. During Open Loop the ECM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the ECM to calculate fuel trim. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short Term Fuel Trim (FT) values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. The fuel trim 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 excessive vapor then a pass is logged. This DTC is continuously monitored during operation. If the ECM detects an excessively rich condition, DTC P0172 or P0175 sets.

DTC Descriptors

This diagnostic procedure supports the following DTCs.

    • DTC P0172 Fuel Trim System Rich Bank 1
    • DTC P0175 Fuel Trim System Rich Bank 2

Conditions for Running the DTC
    • DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0101, P0102, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0103, P0130, P0131, P0132, P0133, P0134, P0135, P0150, P0151, P0152, P0153, P0155, P0201-P0206, P0221, P0222, P0223, P0261, P0262, P0264, P0265, P0267, P0268, P0270, P0271, P0273, P0274, P0276, P0277, P0401, P0402, P0403, P0405, P0406 are not set.
    • The system is in Closed Loop status.
    • The fuel level is more than 9.8 percent.
    • DTC P0172 or P0175 runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The LT FT Cruise/Accel parameter is below -24 percent.
        OR
    • THE LT FT Idle/Decel. parameter is below -7.7 percent.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • 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 consecutive 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.

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive 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 clears after 40 consecutive 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.

Diagnostic Aids
    • A skewed mass air flow (MAF) sensor may set this DTC. Refer to DTC P0101 .
    • Fuel contamination, such as water and alcohol will effect fuel trim.
    • A skewed engine coolant temperature (ECT) sensor may set this DTC.
    • A EVAP purge solenoid that is stuck open may set this DTC.
    • Review Failure Records with a scan tool. If intermittent condition is suspected , refer to Fuel Injector Solenoid Coil Test .

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Important: If any DTCs are set, other than P0172 or P0175, refer to those DTCs before continuing.

  1. Install a scan tool.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for Running the DTC.
  4. Record the LT FT Cruise/Accel and LT FT Idle/Decel parameter values.
  5. Turn OFF the engine.
  6. Turn ON ignition, with engine OFF.
  7. Review the Freeze Frame/Failure Records and record displayed data for this DTC.

Does the scan tool indicate that the LT FT Cruise/Accel parameter is less than the specified value?

-24%

Go to Step 4

Go to Step 3

3

Does the scan tool indicate that the LT FT Idle/Decel. parameter is less than the specified value?

-7.7%

Go to Step 4

Go to Diagnostic Aids

4
  1. Operate engine at idle.
  2. Observe the heated oxygen sensor (HO2S) bank 1 sensor 1 and bank 2 sensor 1 parameters with a scan tool.

Does the scan tool indicate that the HO2S parameter is within the specified range?

0.96-1.04 mV

Go to Step 5

Go to Step 6

5

  1. Turn OFF engine.
  2. Visually and physically inspect the following items:
    3. • The inlet screen of the mass air flow (MAF) sensor for blockage
    • The vacuum hoses for splits, kinks, and proper connection.
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • Inspect for objects blocking throttle body

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6

  1. Turn OFF the engine.
  2. Inspect the HO2S for proper installation.
  3. Verify that the electrical connectors and wires are secured and are not contacting the exhaust system.

Did you find and correct the condition?

--

Go to Step 8

Go to Fuel System Diagnosis

7
  1. Inspect for the following conditions:
    2. • Excessive fuel in the crankcase
    • The evaporative emissions control system
    • The fuel pressure regulator for proper operation--Refer to Fuel System Diagnosis .
  2. Perform the Fuel Injector Balance Test.

Did you find and correct the condition?

--

Go to Step 8

Go to Symptoms - Engine Mechanical in Engine Mechanical

8

Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel.

  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 9

9

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK