Code 23: Mat Temp To Low: Notes

The manifold air temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies 4-6 volts on circuit No. 472 to the sensor. When manifold 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.

1. This test checks to see if Code 23 is the result of a hard failure or an intermittent condition. Code 23 will be displayed if the engine is running for longer than 8 minutes, signal voltage indicates a MAT temperature less than -30°C or there is no VSS signal.
2. This test simulates conditions for a Code 25. If the "SCAN" tester displays a high temperature, the ECM and wiring are okay.
3. This test checks continuity of circuits No. 472 and 452. If circuit No. 452 is open there may also be a Code 21.