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 air-fuel ratio correction value every 0.75 sec. under detecting condition, if an value is within detecting condition for more than 0.3 sec., PCM sets P0172. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Fuel Trim Limits Exceeded | ● Poor connection ● Relevant sensor/actuator ● Blocking of Intake system ● Fuel leakage in injector ● Improper fuel line pressure ● PCM |
Enable Conditions | ● 550rpm ≤ Engine speed ≤ 4000rpm ● 60°C(140°F) ≤ Engine coolant temperature ≤ 115°C(239°F) ● -10°C(14°F) ≤ Intake air temperature ≤ 60°C(140°F) ● 0° ≤ Throttle position ≤ 80° ● 25kPa ≤ Engine load ≤ 90kPa ● 1.5g/s ≤ Intake air flow ≤ 80g/s ● Barometric pressure ≥ 72kPa ● Vehicle speed ≤ 130km/h ● System voltage ≥ 11V ● Feed-back control state ● No other diagnostic fault | |
Threshold value | ● Average of short term fuel trim ＜ 0.8 ● Average of long term fuel trim ＜ 1.23 | |
Diagnosis Time | ● Continuous (More than 0.3 second failure for every 0.75 second test ) | |
MIL On Condition | ● 2 Driving Cycles |
