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 course 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 or P0174 sets.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC P0171 Fuel Trim System Lean Bank 1 |
| • | DTC P0174 Fuel Trim System Lean Bank 2 |
Conditions for Running the DTC
| • | DTCs P0030, P0036, P0050, P0053, P0054, P0056, P0059, P0060, P0101, P0102, P0103, P0106, P0107, P0108, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0200, P0300, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P1133, P1134, P1153, P1154, P2A01, P2A04 are not set. |
| • | The Fuel Trim Learn parameter is enabled. |
| • | The Loop Status parameter is closed. |
| • | The engine coolant temperature (ECT) is between -40 to +139°C (-40 to +282°F). |
| • | The intake air temperature (IAT) is between -20 to +152°C (-4 to +304°F). |
| • | The manifold absolute pressure (MAP) is between 15-105 kPa (2.2-15.2 psi). |
| • | The vehicle speed is less than 132 km/h (82 mph). |
| • | The engine speed is between 400-6,500 RPM. |
| • | The barometric pressure (BARO) is more than 70 kPa (10.7 psi). |
| • | The mass air flow (MAF) is between 1-250 g/s. |
| • | The fuel level is more than 15 percent. |
| • | This diagnostic runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The long term fuel trim value is more than a calibrated value for approximately 3 minutes after the Conditions for Running the DTC have been met.
Action Taken When the DTC Sets
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 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 illuminates the malfunction indicator lamp (MIL) when one of the following occur:
| • | The control module detects the same fuel trim failure during 2 consecutive trips. |
| • | The control module detects any fuel trim failure during any subsequent trip if the conditions at the time of failure meet the following criteria: |
| - | The engine load is within 20 percent of the previous test that failed. |
| - | The engine speed is within 375 RPM of the previous test that failed. |
| - | The engine coolant temperature is in the same range of the previous test that failed. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) at the beginning of the fourth ignition cycle, after 3 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 and related Freeze Frame data clears after 40 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
| • | Excessive resistance in the fuel injector control and/or the ignition 1 voltage circuits may cause the following symptoms: |
| - | A lean condition |
| - | Misfire |
| - | Rough idle |
| - | Refer to DTC P0200 . |
| • | The system may become lean if an injector is not suppling enough fuel. |
| • | A lean condition could be present during high fuel demand. |
| • | Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections . |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
2 | Are any DTCs other than DTC P0171 or P0174 also set? | -- | Go to Step 3 | |||||||||
3 |
Does the scan tool indicate that the long term fuel trim is greater than the specified value? | 24% | Go to Step 4 | Go to Diagnostic Aids | ||||||||
4 |
Does the scan tool indicate that the parameter is within the specified range and fluctuating? | 200-800 mV | Go to Step 5 | Go to Step 6 | ||||||||
5 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 | ||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 8 | Go to Fuel System Diagnosis | ||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 8 | |||||||||
8 |
Important: After repairs, use the scan tool Fuel Trim Reset function to reset the Long Term Fuel Trim.
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 9 | ||||||||
9 | In order to ensure that the performance of the catalyst has not been affected by the fault that set this DTC, operate the vehicle within the conditions for running and setting DTC P0420 or P0430 and verify that DTC P0420 or P0430 runs and passes. Refer to DTC P0420 or P0430 . Does the DTC run and pass? | -- | Go to Step 10 | Go to DTC P0420 or P0430 | ||||||||
10 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
