DTC 31

DTC 31 Mass Air Flow Meter Circuit

Circuit Diagram:

Mass Air Flow Meter Cut-Away:

CIRCUIT DESCRIPTION
The mass air flow meter is an air flow meter which uses a platinum hot wire. The hot wire air flow meter works on the principle that when the electrically heated platinum hot wire is positioned inside the intake air bypass, the intake air volume can be calculated according to the change in the hot wire temperature. This change in temperature is measured by the thermistor at the rear of the hot wire. And feedback from the circuit maintains the hot wire at a set temperature by controlling the current flowing through the hot wire. This current flow is then measured as the output voltage of the air flow meter. The circuit is constructed so that the platinum hot wire and thermistor provide a bridge circuit, with the power transistor controlled so that the potential of (A) and (B) remains equal to maintain the set temperature.





DETECTING CONDITION
If the ECM detects diagnostic trouble code "31", it operates the fail safe function whereby the turbo pressure sensor is used, making it possible to continue to drive the vehicle.





WIRING DIAGRAM

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INSPECTION PROCEDURE