Diagnostic Trouble Code (DTC) Information ECM-251A
Condition
Engine Control Module (ECM) receives information from the rear heated oxygen sensor about fuel/air mixture in different load areas. Internal functions in the control module detect faults in the lambda control.
The diagnostic trouble code (DTC) is stored if the control module detects that:
- Large differences have been measured in fuel/air mixture between the front and rear heated oxygen sensors (HO2S). So large that the trims for the rear heated oxygen sensor are in one of their limit positions.
The control module's test for the diagnostic trouble code (DTC) starts in the event of:
- Normal load (driving) for at least 15 minutes.
NOTE:
The control module can only detect the fault once the test has been started and the diagnostic trouble code (DTC) is stored when the conditions are met.
Substitute Value
- None.
Possible Source
Upper limit
- Contact resistance, oxidation or poor contact in connections.
- Air leakage in the exhaust system.
- Damaged front heated oxygen sensor (HO2S).
- Damaged center heated oxygen sensor (HO2S).
- Damaged rear heated oxygen sensor (HO2S).
Lower limit
- Contact resistance, oxidation or poor contact in connections.
- Damaged front heated oxygen sensor (HO2S).
- Damaged center heated oxygen sensor (HO2S).
- Damaged rear heated oxygen sensor (HO2S).
Fault symptom[s]
- Malfunction indicator light (MIL), on