General Description
In order to provide the best possible combination of drivability, fuel economy and emission control, the PCM uses a closed loop air/fuel metering system. The PCM monitors the HO2S signal voltage and adjusts fuel delivery based it in closed loop fuel control. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The PCM will add fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The PCM will reduce fuel when the HO2S signal is indicating a rich condition. Reduction in fuel is indicated by fuel trim values that are below 0%. The DTC relevant to fuel trim will be set when the amount reaches excessive levels because of a lean or rich condition.
DTC Description
If the correction value of air-fuel ratio is higher than the threshold value, ECM sets DTC P0171.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | Monitor the fuel trim value
| Air leakage
Improper fuel pressure
PCV valve stuck
Clogging of injector
|
Enable Conditions | 12.3%< Engine load < 66%
Engine speed > 500rpm
ECT > 65.3C
IAT < 80C
|
Threshold value | Average of long term fuel trim > 1.23
|
Diagnosis Time | 10 sec
|
MIL On Condition | NO MIL
|