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 lambda controller reaches the maximum or minimum threshold, then feedback control is no longer possible and emissions will be increased. The ECM sets DTC P2188 if no proportional post catalyst fuel trim adaptation occurs for a defined time after the lambda controller has reached its minimum threshold at idle.
DTC Detecting Condition
Item | Detecting Condition | Possible Cause |
DTC Strategy | ? Monitoring deviation of long term fuel trim control in Idle | ? Air restriction in intake or exhaust system ? Front HO2S or MAFS contamination ? Faulty sensor signals ? EVAP system ? Fuel system |
Enable Conditions | ? No relevant failure ? Lambda adaptation active ? Coolant Temp. >73°C(163°F) ? Low estimated fuel dilution in oil |
Threshold Value | ? Idle long term fuel trim has reached in min. limit(-2.5 mg/stroke) for more than 20 sec. |
Diagnostic Time | ? 90 sec. |