Diagnostic Trouble Code (DTC) Information

Diagnostic trouble code (DTC) information ECM-21AC

Condition
The engine control module (ECM) receives information from the heated oxygen sensor (HO2S) about fuel / air mixture at both the upper and lower part-load range. If the fuel / air mixture deviates from lambda=1, the short-term fuel trim will compensate for this by adjusting the injection time so that lambda=1 is achieved. When the short-term fuel trim makes an adjustment, the integrator median must be adjusted by the long-term trim. The diagnostic trouble code (DTC) will be stored when the long-term trim must be adjusted almost to maximum in the upper and lower part-load ranges.
The diagnostic trouble code (DTC) can be diagnosed when driving under specific driving conditions.

Substitute value
None.

Possible source
- Too high ethanol content in fuel.
- Air leakage in the exhaust system
- Low fuel pressure
- Damaged heated oxygen sensor (HO2S).

Fault symptom[s]
- Malfunction indicator lamp (MIL) lit.