GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Rainier - 2WD 🢒 DTC 🢒 DTC P0171

Circuit Description

The powertrain control module (PCM) 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 PCM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During Closed Loop the PCM adds HO2S inputs and level of purge to calculate short and long term fuel trim 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 fuel trim values will be less than 0 percent. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1 This DTC is continuously monitored during engine operation. If the PCM detects an excessively lean condition, DTC P0171 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0171 Fuel Trim System Lean

Conditions for Running the DTC
    • DTCs P0013, P0014, P0016, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0201-P0206, P0220, P0300, P0301-P0306, P0326, P0327, P0341, P0446, P0483, P0496, P0502, P0503, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P1133, P1516, P1680, P2101, P2120, P2125, P2135, P2138, P2176 are not set.
    • The engine is in Closed Loop status.
    • The engine coolant temperature (ECT) is between 60-125°C (140-257°F).
    • The intake air temperature is between -25 and +150°C (-13 and +302°F).
    • The manifold absolute pressure (MAP) is more than 26 kPa (3.8 psi).
    • The vehicle speed is less than 132 km/h (82 mph).
    • The engine speed is between 400-5,850 RPM.
    • The barometric pressure is more than 70 kPa (10.2 psi).
    • The fuel level is more than 10 percent.
    • DTC P0171 runs continuously when the above conditions are met.

Conditions for Setting the DTC

The average long term fuel trim value is above 20 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
    • Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • The system will go lean if an injector is not supplying enough fuel.
    • A lean condition could be present during high fuel demand due to a fuel pump that does not pump enough fuel.
    • Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Intermittent Conditions .

Test Description

The number below refers to the step number on the diagnostic table.

  1. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

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

Are any DTCs other than P0171 also set?

--

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

Go to Step 3

3
  1. Install a scan tool.
  2. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.
  3. Select the Fuel and Emission data list.
  4. Start the engine.
  5. Observe the Long Term FT parameter with a scan tool.

Is the Long Term FT parameter more than the specified value?

20%

Go to Step 4

Go to Diagnostic Aids

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

Does the scan tool indicate that the HO2S parameters are within the specified range and fluctuating?

200-800 mV

Go to Step 5

Go to Step 6

5
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
    3. • Splits, kinks, or improper connections at the vacuum hoses--Refer to Emission Hose Routing Diagram .
    • Low fuel pressure--Refer to Fuel System Diagnosis .
    • Properly functioning fuel injectors--Refer to Fuel Injector Solenoid Coil Test
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

6
  1. Turn OFF the engine.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the manifold absolute pressure (MAP) sensor pressure parameter with a scan tool.
  4. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .

Do the MAP parameters indicate the correct barometric pressure?

--

Go to Step 7

Go to DTC P0106

7
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    3. • Proper HO2S installation
    • Electrical connectors and wires are secured and not contacting the exhaust system
    • An open or a short to ground in the HO2S signal circuit

Did you find and correct the condition?

--

Go to Step 9

Go to Fuel System Diagnosis

8

  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    3. • AIR shut-off valve stuck open
    • Missing, loose, or leaking exhaust components
    • Vacuum leaks at the intake manifold, throttle body, and injector O-rings
    • Leaks at the air intake ducts
    • Leaking crankcase ventilation system

Did you find and correct the condition?

--

Go to Step 9

Go to Symptoms - Engine Mechanical in Engine Mechanical

9

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

  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 10

10

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