Circuit Description

The MAF (Mass Air Flow) meter measures the amount of air flowing through the throttle valve. The ECM uses this information to determine the fuel injection time and provide a proper air-fuel ratio. Inside the MAF meter, there is a heated platinum wire exposed to the flow of intake air.

By applying a specific current to the wire, the ECM heats this wire to a given temperature. The flow of incoming air cools the wire and an internal thermistor, changing their resistance. To maintain a constant current value, the ECM varies the voltage applied to these components in the MAF meter. The voltage level is proportional to the airflow through the sensor and the ECM interprets this voltage as the intake air amount.

The circuit is constructed so that the platinum hot wire and temperature sensor provide a bridge circuit, with the power transistor controlled so that the potential of A and B remains equal to maintain the set temperature.

Fig 1: Mass Or Volume Air Flow Circuit High Input Circuit Diagram

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC Detection Condition Table

HINT:

After confirming DTC "P0100, P0102 or P0103", use the hand-held tester or the OBD II scan tool to confirm the mass air flow ratio from the "DIAGNOSIS/ENHANCED OBD II/DATA LIST/ALL."

Fig 3: Mass Air Flow Value Malfunction Table