Circuit Description
The engine control module (ECM) 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 ECM determines fuel delivery based on sensor signals, without oxygen sensor (O2S) input. During Closed Loop, the ECM 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 ECM 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 -25-115°C (-13-239°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 average long term fuel trim 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 | |||||||||
2 | Are any DTCs other than P0171 also set? | -- | Go to Step 3 | |||||||||
3 |
Does the scan tool indicate that the Long Term FT parameter is more than the specified value? | 29% | Go to Step 4 | Go to Diagnostic Aids | ||||||||
4 |
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 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 8 | ||||||||
6 |
Do the MAP parameters indicate the correct barometric pressure? | -- | Go to Step 7 | Go to DTC P0105 | ||||||||
7 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Fuel System Diagnosis | ||||||||
8 |
Did you find and correct the condition? | -- | Go to Step 9 | Go to Symptoms - Engine Mechanical in Engine Mechanical. | ||||||||
9 |
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? | -- | System OK |
