Diagnostic Trouble Code (DTC) Information

Diagnostic trouble code (DTC) information EFI-121

EFI-121 Mass air flow (MAF) sensor, signal

Condition




Diagnostic trouble code (DTC) EFI-121 is stored if the signal from the mass air flow (MAF) sensor is lower than 0.2 V or greater than 2.2 V at idling speed, or is outside its permitted range for engine speed (RPM) and throttle angle.

Substitute value
- the engine control module (ECM) uses engine speed (RPM) and throttle angle to determine load
- idle air trim adaptation disabled
- long-term fuel trim disabled
- EVAP-diagnostic disabled.

Possible source

Signal too high:
- short-circuit to supply voltage in signal cable
- open-circuit in cable to signal or power ground
- defective mass air flow (MAF) sensor
- contact resistance in terminals.

Signal too low:
- defective fuse 11B/2 (1998-)
- Open-circuit in signal- or power cable
- short-circuit to ground in signal cable.
- fresh air hose damaged or loose
- defective mass air flow (MAF) sensor
- contact resistance in terminals.

Fault symptom[s]
- uneven idling and/or running