General Description
In order to provide the best possible combination of drivability, fuel economy and emission control, the ECM uses a closed loop air/fuel metering system. The ECM 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 ECM 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 ECM 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 fuel trim values reaches the maximum or minimum threshold, then feedback control is no longer possible and emissions will be increased. The ECM sets DTC P0170 if no proportional fuel adaptation occurs for a defined time after the short term fuel trim has reached its minimum or maximum threshold.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | ? Monitoring deviation of short term fuel trim control | ? Air leakage or restriction in intake or exhaust system ? Dirty engine oil or oil level too high ? Front HO2S or MAFS contamination ? Fuel system ? EVAP system ? Faulty sensor signals |
Enable Conditions | ? No relevant failure ? Lambda control active ? Coolant temperature>73°C(163°F) |
Threshold Value | ? +50 % < Short Term Trim < -30 % |
Diagnostic Time | ? 90sec. |