Code 23: Mat Signal Temp Low (2.5L): Notes

The ECM supplies and monitors a voltage signal (4-6 volts) to the sensor. When temperatures are low, sensor resistance is high and the ECM will see a high-monitored voltage signal. As temperature increases, sensor resistance decreases and voltage sensed by the ECM drops.

Test Number 1)  This checks if Code 23 is a hard failure or an intermittent condition. Code 23 will set if engine is running for one minute, MAT sensor temperature is less than -22°F (-30°C) and speed sensor signal is not present.

Test Number 2)  This simulates conditions for a Code 25. If the "Scan" tester displays a high temperature, the ECM and wiring are not at fault.

Test Number 3)  This checks for continuity of sensor signal and ground circuits.