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.
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 P2099 if no proportional post catalyst fuel trim adaptation occurs for a defined time after the lambda controller has reached its maximum threshold.
Item | Detecting Condition | Possible cause |
DTC Strategy |
•
Fuel Trim Rear Sensor Control Limits Exceeded |
•
Air leakage in exhaust System
•
HO2S
•
TWC |
Enable Conditions |
•
Cell Enabled
•
Barometric Pressure ≥ 74 kPa
•
Intake Air Temperature ≥ -10 ℃
•
System Voltage ≥ 10.9936 V
•
Closed Loop Active
•
BLM learn Allowed
•
Disabling Fault not present | |
Threshold value |
•
Front O2 Sensor switch point ≤ 0.4V Rear O2 Sensor Voltage > 0.82V | |
Diagnosis Time |
•
Fail count > 30 within 80 samples 250ms continuous loop | |
MIL On Condition |
•
2 Driving Cycle |
