Code 25, Intake Air Temp Sensor CKT/High Temp Indicated

IAT sensor uses a thermistor to control signal voltage to ECM. ECM applies 4-6 volts on Red/Black wire to the sensor. When intake air is cold, sensor resistance is high. ECM will sense high signal voltage. As intake air temperature warms, sensor resistance decreases, and voltage drops.

1. Code 25 is set if signal voltage indicates intake air temperature is more than 284°F (140°C), or signal circuit is grounded for 5 seconds. Code 25 will set if sensor or wire is open, or faulty connection exists in circuit.
2. If resistance is greater than 14,800 ohms, replace sensor.

Fig 1: Code 25 Flow Chart, IAT Sensor Ckt./High Temp. Indicated

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 25 Schematic, IAT Sensor Ckt./High Temp. Indicated

Courtesy of GENERAL MOTORS CORP.