Page 6E2-52 DOHC Code 23A MAT Sensor Low Temp.

Fig. 6E2-34:

6E2-52 DRIVEABILITY AND EMISSIONS (DOHC)

CODE 23A

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


Circuit Description:

The Manifold Air Temperature Sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6 volts) to CKT 472 of 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.

MAT LOW Test Description:

Numbers below refer to circled numbers on the diagnostic chart.

(1) This step checks to see if Code 23A is the result of a hard failure or an intermittent condition.
A Code 23A will set if:
^ Signal voltage indicates a MAT temperature less than -30~C
^ Engine has been running for longer than 4.25 minutes.

(2) This test simulates conditions for a Code 23B. If the "Scan" tool displays a high temperature, the ECM
and wiring are OK.
(3) This step checks continuity of CKT's 472 and 452. If CKT 452 is open there may also be a Code 21A.

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 nearly the same. A Code 23A will result if CKT's 472 or 452 become open. If Code 23A is intermittent, refer to Section "B".