Diagnostic trouble code (DTC) information ECM-121B
Condition
The engine control module (ECM) calculates the expected mass air flow. The calculation is based on a number of different parameters. The calculated value for mass air flow is then compared with the measured value from the mass air flow (MAF) sensor.
The diagnostic trouble code (DTC) is stored if the engine control module (ECM) detects that the correction factor for the air mass (measured air mass/desired air mass value) is too low, while the long-term fuel trim is above or below a set value.
The diagnostic trouble code (DTC) can be diagnosed when the engine is running.
Substitute Value
- Calculated boost pressure
- Calculated air mass
- Rear heated oxygen sensor (HO2S) control shut off
- Misfire diagnostic shut off.
Possible Source
- Contact resistance or oxidation in the mass air flow (MAF) connectors
- Air leakage in the intake system
- Blocked intake system
- Damaged mass air flow (MAF) sensor.
Fault symptom[s]
- Malfunction indicator lamp (MIL) lit
- Poor performance.