For 1990-2009 cars

### 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 oxygen sensor (O2S) input. During Closed Loop, the PCM adds oxygen sensor inputs to calculate the short and long term fuel trim. If the oxygen sensors indicate a lean condition, the fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the heated oxygen sensor (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.

### Conditions for Running the DTC

• | DTCs P0105, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123 , P0125, P0128, P0130-P0134, P0201, P0217, P0300, P0301-P0304, P0326, P0327, P0336, P0340, P0341, P0446, P0502, P0503, P0601, P0602, P1441 are not set.

• | The engine coolant temperature (ECT) is between 60-115°C (140-239°F).

• | The intake air temperature (IAT) is between -25 to +115°C (-13 to +239°F).

• | The manifold absolute pressure (MAP) is more than 28 kPa (4.06 psi).

• | The vehicle speed is less than 132 km/h (82 mph).

• | The engine speed is between 550-3,600 RPM.

• | The barometric pressure (BARO) is more than 72 kPa (10.4 psi).

• | The fuel level is more than 9.8 percent.

### Conditions for Setting the DTC

• | The Fuel Trim Index value is above 29 percent.

• | The above condition is present for 16 seconds.

### 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 become lean if a fuel 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.

• | Fuel contamination, such as water and alcohol will effect the fuel trim.

• | Use a scan tool in order to review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions .

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 | Are any DTCs other than P0171 also set? | -- | Go to Diagnostic Trouble Code (DTC) List | 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 Fuel and Emissions Data List.
4. Start the engine and observe the Fuel Trim Index parameter.

Does the scan tool indicate that the Fuel Trim Index parameter is more than the specified value?

29%

Go to Step 4

Go to Diagnostic Aids

4 |

1. Operate the engine at idle.
2. Observe the O2S parameters with a scan tool.

Does the scan tool indicate that the O2S 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:

• | Splits, kinks, and proper connections at the vacuum hoses--Refer to Emission Hose Routing Diagram .

• | Low fuel pressure--Refer to Fuel System Diagnosis .

• | 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 .

Does the MAP parameter indicate the correct barometric pressure?

--

Go to Step 7

Go to DTC P0105

7 |

1. Turn OFF the engine.
2. Inspect for the following conditions:

• | Proper O2S installation

• | Electrical connectors and wires are secured and not contacting the exhaust system.

3. A short between the signal circuit and the low reference or ground 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:

• | 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 | System OK