Description
DATA TROUBLE CODE: 31SYSTEM: Mass Air Flow Meter Circuit
CIRCUIT WIRING DIAGRAM
CIRCUIT DESCRIPTION
Fig.19 - Exploded View Of The Mass Air Flow Sensor. The Platinum Hotwire And The Thermister Form A Bridge Circuit.:
Fig.19
The hot wire air flow meter works on the principle that when an 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.
Fig.20 - Schematic View Of Mass Air Flow Meter Internal Circuit:
Fig.20
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 and A and B (see Fig.20) remains equal to maintain the set temperature.
NOTE: 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.
DIAGNOSTIC TROUBLE CODE DETECTING CONDITION
- Open or short in mass air flow meter circuit for 3 seconds or more with engine speed less than 3,000 rpm.
TROUBLE AREA
- Open or short in mass air flow meter circuit
- Mass air flow meter
- ECM