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 heated oxygen sensor (HO2S) input. During Closed Loop, the ECM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicate a lean condition, the fuel trim values will be above 0 percent. If the HO2S 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. This DTC is continuously monitored during engine operation. If the ECM detects an excessively lean condition, DTC P0171 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0171 Fuel Trim System Lean
Conditions for Running the DTC
| • | DTCs P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123 , P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0201-P0204, P0220, P0300, P0301-P0304, P0336, P0340, P0341, P0442, P0446, P0452, P0453, P0455, P0481, P0496, P0502, P0506, P0601, P0602, P0604, P0606, P060D, P060E, P062F, P0641, P0651, P0700, P0701, P1133, P1516, P1621, P2101, P2120, P2125, P2135, P2138, P2176 are not set. |
| • | The engine is in Closed Loop status. |
| • | The engine coolant temperature (ECT) is between 60-125°C (140-257°F). |
| • | The intake air temperature (IAT) is between -25 to +150°C (-13 to +302°F). |
| • | The manifold absolute pressure (MAP) is more than 26 kPa (3.8 psi). |
| • | The vehicle speed is less than 132 km/h (82 mph). |
| • | The engine speed is between 400-5,700 RPM. |
| • | The barometric pressure (BARO) is more than 72 kPa (10.4 psi). |
| • | DTC P0171 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
| • | The average long term fuel trim value is above 21 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, or a restricted fuel pipe. |
| • | Fuel contamination, such as water and alcohol will effect the fuel trim. |
| • | Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to Testing for Intermittent Conditions and Poor Connections . |
| • | Test for fuel contamination. Small amounts of water can be delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
2 |
Important: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators. Are any DTCs other than P0171 also set? | -- | Go to Step 3 | |||||||||
3 |
Is the Long Term FT parameter more than the specified value? | 21% | Go to Step 4 | Go to Diagnostic Aids | ||||||||
4 |
Does the scan tool indicate that the HO2S 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 P0106 | ||||||||
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 | |||||||||
9 |
Important: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle. Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 10 | ||||||||
10 | To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 . Did you complete the procedure? | -- | Go to Step 11 | -- | ||||||||
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |
