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 to calculate 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 (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, this DTC will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123 , P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206 P0300, P0401, P0403, P0404, P0404, 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 is between 18- 70°C (64-158°F). |
| • | The manifold absolute pressure (MAP) is between 18-105 kPa (2.6-15.2 psi). |
| • | The vehicle speed is less than 132 km/h (82 mph). |
| • | The engine speed is between 550-4,000 RPM. |
| • | The barometric pressure 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. |
Conditions for Setting the DTC
| • | The average long term fuel trim value is above 20 percent. |
| • | All of the above conditions are present for 6 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 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 affect the fuel trim. |
| • | Use a scan tool in order to review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the conditions were not corrected, refer to Fuel System Diagnosis for a possible fuel condition.
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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 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 | ||||||||||
Turn OFF the engine.
If conditions were not corrected, refer to HO2S DTCs for specific testing. Did you find and correct the condition? | -- | Go to Step 7 | Go to Fuel System Diagnosis | |||||||||||
Operate the engine at idle.
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.
Does the DTC run and pass? | -- | Go to Step 8 | Go to Step 2 | ||||||||||
8 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
