Code 23, IAT Sensor Circuit, High/Low Temperature Indicated: Notes

Intake Air Temperature (IAT) sensor uses a thermistor to control signal voltage to ECM. ECM applies voltage on Blue/Black wire to sensor. When intake manifold air is cold, sensor (thermistor) resistance is high and ECM senses high signal voltage. As intake air warms, sensor (thermistor) resistance decreases, and voltage drops.

1. Checks if Code 23 is due to a hard failure or an intermittent condition. Code 23 will set under the following conditions:

   High temperature

   • Engine has been running for longer than 2 minutes
   • Signal voltage indicates IAT temperature is less than -36°F (-38°C).

   Low temperature

   • IAT temperature is greater than 390°F (199°C).
   • Condition is detected for at least 2 minutes.
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.