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.
Checking the fuel trime value under detecting condition, if its average exceeds the limit over certain period, PCM sets P0171. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy |
•
Monitoring deviation of short term fuel trim control | 1. Air leakage 2. Improper fuel pressure 3. PCV valve stuck 4. Clogging of injector |
Enable Conditions |
•
No Failure detection for DTCs | |
Threshold value |
•
Short term trim value at MAX Limit for more thin 40sec of total monitoring time
•
short term trim ＞ +50% | |
Diagnosis Time |
•
90 sec | |
MIL On Condition |
•
2 Driving Cycles |
