GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2003 🢒 L300/LW300 🢒 Engine 🢒 Engine Controls - 3.0L (L81) 🢒 DTC P0171 or P0174

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 Loop and Closed Loop. During Open Loop the ECM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the ECM adds oxygen sensor inputs 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. This DTC is continuously monitored during engine operation. If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.

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.

Conditions for Setting the DTC
    • The LT FT Cruise/Accel parameter is above 24 percent.
        OR
    • The LT FT Idle/Decel. parameter is above 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 .
    • The system will go lean if an injector is not suppling enough fuel.
    • The system will go lean during high fuel demand.
    • An EGR valve stuck open may set this DTC.
    • A skewed engine coolant temperature (ECT) sensor may set this DTC.
    • Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Fuel Injector Solenoid Coil Test .

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Important: If any DTCs are set, other than P0171 or P0174, refer to those DTCs before continuing.

  1. Install the 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 the ignition, with the engine OFF.
  7. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.

Does the scan tool indicate that the LT FT Cruise/Accel parameter is more 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 more 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 the engine.
  2. Visually and physically inspect the following items:
    3. • Vacuum hoses for splits, kinks, and proper connections.
    • Ensure that the vehicle has sufficient fuel. If fuel pressure is too low this DTC may set. Refer to Fuel System Diagnosis .
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

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 not contacting the exhaust system.

Did you find and correct the condition?

--

Go to Step 8

Go to Fuel System Diagnosis

7
  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    3. • Missing, loose, or leaking exhaust components--Refer to Exhaust Leakage in Engine Exhaust.
    • Vacuum leaks at the intake manifold and injector O-rings
    • The air induction system and air intake ducts for vacuum leaks.
    • The crankcase ventilation system for leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.
    • A skewed mass air flow (MAF) sensor--Refer to DTC P0101 .

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. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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

System OK