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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Grand Prix 🢒 Accessories 🢒 Navigation Systems 🢒 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 and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs and level of purge to calculate Short and Long Term fuel trim adjustments. 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. The values for the Short Term fuel trim change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an Air/Fuel Ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The PCM selects the cells based on the engine speed and engine load. 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 Bank 1

Conditions for Running the DTC
    • DTCs P0030, P0036, P0053, P0054, P0068, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0120, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0300, P0401, P0403, P0404, P0405, P0406, P0420, P0442, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0462, P0463, P0464, P0496, P0506, P0507, P1133, P1134, P1404, P1516, P2101, P2107, P2108, P2119, P2120, P2125, P2135, P2138, P2A00, P2A01 are not set.
    • The engine is in Closed Loop status.
    • Fuel Trim Learn is enabled.
    • The engine coolant is between 38.5-121°C (101.3-250°F).
    • The intake air temperature (IAT) is between -38.5 and +140°C (-37.3 and +284°F).
    • The manifold absolute pressure (MAP) is between 15-99 kPa (2.1-28.8 psi).
    • The vehicle speed is less than 132 km/h (82 mph).
    • The engine speed is between 525-5,600 RPM.
    • The barometric pressure (BARO) is more than 70 kPa (10.1 psi).
    • The idle purge is enabled.
    • The mass air flow (MAF) is between 1-150 g/s.
    • The fuel level is more than 10 percent.
    • The scan tool special functions are not active.

Conditions for Setting the DTC
    • The average Long Term fuel trim is above 18.8 percent.
    • The above condition is present for more than 2 minutes.
    • This diagnostic runs continuously.

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
    • 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.
    • Excessive resistance in the ignition 1 voltage and/or the fuel injector circuits may cause the following symptoms:
       - A lean condition
       - Misfire
       - Rough idle
    • Fuel contamination, such as water and alcohol, will effect the fuel trim.
    • Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections .
    • This DTC may set due to poor idle characteristics as a result of uncontrolled fueling caused by an open or high resistance in the HO2S 1 low signal circuit. Before replacing any component ensure that this condition does not exist.

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 failure 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

2

Are any DTCs other than DTC P0171 also set?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 3

3
  1. Install the scan tool.
  2. Turn ON the ignition.
  3. Observe the Freeze Frame/Failure Records parameter with a scan tool and record the displayed data for this DTC.
  4. Start and idle the engine at normal operating temperature in the Closed Loop.
  5. Observe the Long Term FT parameter.

Does the scan tool indicate that the Long Term fuel trim is more than the specified value?

18.8%

Go to Step 4

Go to Diagnostic Aids

4
  1. Operate the engine at idle.
  2. Observe the HO2S 1 parameter with a scan tool.

Does the scan tool indicate that the heated oxygen sensor (HO2S) voltages 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. • Vacuum hoses for splits, kinks, and proper connections--Refer to Emission Hose Routing Diagram .
    • Ensure that the vehicle has sufficient fuel in the tank. If the fuel pressure is too low, this DTC may set. Refer to Fuel System Diagnosis .
    • Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Any lean fuel injectors--Refer to Fuel Injector Balance Test with Tech 2 .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

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. Refer to Altitude Versus Barometric Pressure .
  4. The MAP sensor parameter should be within the range specified for your altitude.

Does the MAP indicate the correct barometric pressure?

--

Go to Step 7

Go to Manifold Absolute Pressure Sensor Diagnosis

7
  1. Turn OFF the engine.
  2. Inspect the HO2S for proper installation. Refer to Heated Oxygen Sensor 1 Replacement .
  3. Ensure that the electrical connectors and wires are secured and not contacting the exhaust system.

Did you find and correct the condition?

--

Go to Step 11

Go to Step 8

8

Test the HO2S 1 low signal circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 9

9

Test for a short between the signal circuit and the low reference circuit or ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Fuel System Diagnosis

10

  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    3. • Missing, loose, or leaking exhaust components, from the HO2S forward--Refer to Symptoms - Engine Exhaust .
    • Vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
    • Air induction system and the air intake ducts for leaks or for a missing air filter element--Refer to Air Cleaner Assembly Replacement and Air Cleaner Inlet Duct Replacement .
    • Evaporative canister purge lines plugged or obstructed
    • Properly functioning fuel injectors--Refer to Fuel Injector Solenoid Coil Test .
    • Crankcase ventilation system for leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis .

Did you find and correct the condition?

--

Go to Step 11

Go to Symptoms - Engine Mechanical

11

Important: Reset the Long Term Fuel Trim with the scan tool Fuel Trim Reset function after any of the above repairs.

  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 in 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 12

12

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

System OK