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.
f the lambda controller reaches the maximum or minimum threshold, then feedback control is no longer possible and emissions will be increased. The PCM sets DTC P2097 if no proportional post catalyst fuel trim adaptation occurs for a defined time after the lambda controller has reached its minimum threshold.
Item
Detecting Condition
Possible Cause
DTC Strategy
Monitoring deviation of down HO2S feedback control
Exhaust System
HO2S
TWC
Enable Conditions
Lambda control active
No relevant failure
Dynamic fuel trim is active
Canister purge valve not opening or closing
Threshold Value
Adaptation value < -500 msec.
Diagnostic Time
90sec.
MIL On Condition
2 Drive Cycles
? Sector A : Signal Normal
? Sector B : Signal Fluctuation by rapid acceleration
? Sector C : Signal Recovery