Diagnostic trouble code (DTC) information ECM-121D
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 value for the measured air mass is lower than the calculated value for air mass.
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
- Air leakage in the intake system
- Contact resistance in the mass air flow (MAF) sensor connectors
- Short-circuit to ground in the signal cable
- Open-circuit in the signal cable
- Open-circuit in the power supply
- Damaged mass air flow (MAF) sensor.
Fault symptom[s]
- Malfunction indicator lamp (MIL) lit
- Poor performance.