DTC 25

Code Chart 25:

IAT Sensor Circuit:

CIRCUIT DESCRIPTION:
The Intake Air Temperature (IAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (about 5 volts) on CKT 472 to the sensor when intake air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.

The IAT sensor is located in the air cleaner.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 25 will set if:

^ Signal voltage indicates an intake air temperature greater than 145°C (293°F) for 2 seconds.
^ Time since engine start is 4 minutes or longer.
^ A vehicle speed is present.

DIAGNOSTIC AIDS:
A scan tool reads temperature of the air entering the engine and should read close to ambient air temperature, when engine is cold, and rises as underhood temperature increases.

A faulty connection, or an open in CKT 472 or 452 will result in a DTC 23. - Intermittent Malfunctions