Page 6E3-38 DOHC Turbo Code 23 MAT Sensor Low Temp.

Fig. 6E3-19:

6E3-38 DRIVEABILITY AND EMISSIONS (DOHC TURBO)

CODE 23

MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)


Circuit Description:

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a 5 volt reference voltage (4-6 volts) to BLU/BLK wire to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less and the voltage drops.

Test Description:

Numbers below refer to circled numbers on the diagnostic chart.
(1) This step checks to see if Code 23 is the result of a hard failure or, an intermittent condition.
A Code 23 will set if:
^ Engine has been running for longer than 1 minutes.
^ Signal voltage indicates a MAT temperature less than -38~C ( 36.4~F).
(2) This test simulates conditions for a Code 25. If the "Scan" tool displays a high temperature, the ECM
and wiring are OK.
(3) This step checks continuity of BLU/BLK wire and BLK/WHT wire. If BLK/WHT wire is open, there may
also be a Code 22.

Diagnostic Aids:

If the engine has been allowed to cool to an ambient temperature (overnight), Coolant and MAT temperatures may be checked with a "Scan" tool and should read close to each other. A Code 23 will result if BLU/BLK wire or BLK/WHT wire become open. If Code 23 is intermittent, refer to "Symptoms", Section "6E3-B".