Circuit Description

WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.

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 provides 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, affecting 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. 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 Description Chart

Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Fig 2: DTC P0100, P0102 And P0103 Diagnostic Chart

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

Fig 3: Air Flow Rate And Malfunction Table