Code 23A: Mat Sensor CKT (Lo Temp Indicated): Notes
The MAT sensor uses a thermistor to control signal voltage to the ECM. The ECM applies 4-6 volts on circuit No. 472 to MAT sensor. When manifold air is cold, sensor resistance is high and ECM will see a high voltage. As air temperature increases, sensor resistance decreases and the voltage drops.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This determines if Code 23A is result of a hard failure or an intermittent condition. Code 23A will set if engine is running longer than 2 minutes and signal voltage indicates a MAT temperature below -22°F (-30°C).
- This step simulates conditions for a Code 23B. If Scan tester displays a high temperature, ECM and wiring are okay.
- This step checks continuity of circuit No. 452 and 472. If circuit No. 452 is open, a Code 21A may be present.