Code 23A - Mat Circuit (Low Temperature Indicated): Notes

Manifold Air Temperature (MAT) sensor uses a thermistor to control signal to ECM. ECM applies and monitors 4-6 volts to sensor. When manifold air is cold, sensor resistance is high and ECM will see a high MAT signal. As air warms, sensor resistance drops and MAT signal drops.

1. Code 23A will set if engine has been running for longer than 3 minutes and signal voltage indicates MAT less than -86°F (-30°C).
2. This simulates conditions for Code 23B. If scan tester reads high temperature, ECM and wiring are okay.
3. This checks continuity of circuits. If circuit is open, Code 21A may also set.