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, fuel delivery adjustments. 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. If the PCM detects an excessively lean condition, diagnostic trouble code (DTC) P0171 sets.
• | DTCs P0101-P0103, P0107, P0108, P0121- P0123 , P0130-P0135, P0137, P0138, P0140, P0141, P0201-P0206, P0300, P0401, P0403-P0405, P0410, P0440, P0442, P0446, P0506, P0507, P1404, or P1441 are not set. |
• | The engine coolant temperature (ECT) is between 20-110°C (68-230°F). |
• | The intake air temperature (IAT) is between 18-70°C (64-158°F). |
• | The manifold absolute pressure (MAP) is between 15-105 kPa (2.1-15.2 psi). |
• | The vehicle speed is less than 132 km/h (82 mph). |
• | The engine speed is between 550-4,000 RPM. |
• | The barometric pressure (BARO) is more than 70 kPa (10.1 psi). |
• | The mass airflow (MAF) is between 2.8-150 g/s. |
• | The fuel level is more than 10 percent. |
• | The average long term fuel trim value is above 20 percent. |
• | All of the above conditions are present for 6 seconds. |
• | 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. |
• | 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. |
• | 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. |
• | 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 . |
The numbers below refer to the step numbers on the diagnostic table.
If the conditions were not corrected, refer to Fuel System Diagnosis for a possible fuel condition.
If the 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-Engine Controls? | -- | Go to Step 2 | |||||||||||
2 |
Important: If any DTCs are set, other than DTC P0171, refer to those DTCs before continuing.
Does the scan tool indicate that the long term fuel trim is greater than the specified value? | 23% | Go to Step 3 | Go to Diagnostic Aids | ||||||||||
3 |
Does the scan tool indicate that the values are within the specified range and fluctuating? | 200-800 mV | Go to Step 4 | Go to Step 5 | ||||||||||
4 |
Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 | ||||||||||
Did you find and correct the condition? | -- | Go to Step 7 | Go to Fuel System Diagnosis | |||||||||||
Did you find and correct the condition? | -- | Go to Step 7 | Go to Symptoms - Engine Mechanical in Engine Mechanical | |||||||||||
7 |
Important: After any of the above repairs, use the scan tool Fuel Trim Reset function in order to reset the long term fuel trim.
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 8 | ||||||||||
8 | Observe Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |