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Home >> Pontiac >> 1989 >> LeMans Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Tests W/Codes >> Diagnostic Circuit Check & Code Charts >> Code 23, Mat Temp Low >> Code 23, Manifold Air Temperature (Mat) Sensor (Temperature Too Low)

Code 23, Manifold Air Temperature (Mat) Sensor (Temperature Too Low)

The MAT sensor uses a thermistor type resistor to control signal voltage to the ECM. A 4-6 volt reference signal is supplied to the sensor on circuit on circuit No. 472. When manifold air temperature is cold, sensor resistance is high and the ECM will see a high signal voltage. As the manifold air temperature increases, sensor resistance becomes less and voltage drops.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. This step checks if Code 23 is a result of a hard failure or an intermittent condition.

    A Code 23 will set if:

    • Signal voltage indicates a MAT temperature of less than -22°F (-30°C).
    • Engine has been running longer than 58 seconds.
  2. This test simulates conditions for a Code 25 (high MAT temperature). If the "Scan" tester displays a high temperature, the ECM and wiring are okay.
  3. This step checks continuity of circuits No. 472 and 452. If circuit No. 452 is open, there may also be a Code 33 set.
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