For 1990-2009 cars

The mass airflow (MAF) sensor measures the speed and density of air entering the intake manifold. The ECM converts this input to a mass of air per unit time to correctly fuel the engine. The MAF output voltage is a function of the power required to keep the sensing element at a fixed temperature above outside air temperature as the incoming air cools the sensing elements. The MAF sensor signal voltage varies between 0.14-4.8 volts under all normal engine running conditions. As a validity check, the ECM calculates airflow based on engine speed, throttle plate position, intake air temperature and engine coolant temperature, then compares this to the actual reading from the MAF sensor. DTC P0101 will set if the ECM determines the calculated airflow value and actual airflow value are not within a calibrated range.

### DTC Parameters

DTC P0101 will set if the MAF sensor airflow value is too far out of agreement from the ECM calculated airflow value (based on MAP, engine speed and TP angle) when:

• | Ratio of TP sensor 1 to TP sensor 2 signal voltage is less than 0.5 (TP angle is less than 30%)

• | TP sensor 1 and TP sensor 2 signal deviate less than 0.6% (TP sensor signal voltages correlate with each other within range)

• | MAP sensor signal voltage is less than 0.95 volts

• | STFT is within -7.7 to 7.7% at idle, and within -24 to 24% at cruise/accel

DTC P0101 diagnostic runs continuously once the above conditions have been met.

P0101 is a type B DTC.

### Diagnostic Aids

Important: If DTC P0102 or P0103 is also set, diagnose that DTC first. DTC P0101 may also set if a circuit fault exists in the MAF sensor circuit.

Using the scan tool, verify MAF reads 0.0 g/s (near 1.02 volts) with ignition ON and engine OFF.

Check the following for possible causes of MAF rationality errors:

• | Vacuum leaks

• | Air induction tubing is cracked or loose

• | Throttle plate is restricted or there is carbon buildup

• | MAF sensor harness connector or reference return circuit 652 is corroded or has spread terminals

• | MAF sensor is skewed at different engine load ranges. Compare MAF sensor voltage readings on the scan tool with a known good vehicle under the same operating conditions.