Code 23, Intake Air Temp (IAT) Sensor CKT, Low Temp Indicated: Notes

IAT sensor uses a thermistor to control signal voltage to ECM. ECM applies 4-6 volts on Blue/Black wire to sensor. When intake manifold air is cold, the sensor (thermistor) resistance is high and ECM senses a high voltage. As intake air warms, sensor resistance drops, and voltage drops.

1. This checks if Code 23 is due to a hard failure or an intermittent condition. Code 23 is set if engine is running longer than 2 minutes and signal voltage indicates IAT temperature is less than -22°F (-30°C).
2. Simulates conditions for a Code 23 (high temperature indicated). If scan tester displays a high temperature, ECM and wiring are okay.
3. Checks continuity of Blue/Black and Black wires. If Black wire is open, Code 21 may also be present.