Code 31, Mass Airflow Sensor/Short Circuit

The Mass Airflow (MAF) sensor measures air passing through it in a given time. The ECM uses this information to monitor engine operating condition and calculate fuel delivery. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle.

The MAF sensor produces a frequency signal that cannot be easily measured. The MAF sensor also contains fuel pump control switch. The fuel pump control switch is closed when engine is running. This provides ground to circuit opening relay to activate fuel pump.

1. Verifies B+ and ground at MAF sensor.
2. Verifies proper voltage control to ECM from MAF sensor.
3. Verifies proper voltage from MAF sensor with engine RPM.