Powertrain Controls - ECM/PCM

DTC 25 Intake Air Temperature Sensor:

Intake Air Temperature Sensor Wiring Diagram:

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 the air is cold, the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. If the air is warm the sensor resistance is low, therefore the ECM will see a low voltage.

The IAT sensor is located in the rear air intake duct.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 25 will set if:

^ A signal voltage indicates an Intake Air Temperature (IAT) greater than 145°C (293°F) for 2 second.
^ A vehicle speed greater than 1 mph is present.
^ Due to the conditions necessary to set a DTC 25 the MIL (Service Engine Soon) will remain 'ON" while the signal is low and 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 short to ground in CKT 472 will result in a DTC 25.

The "Temperature VS. Resistance Values" scale may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor. A shifted sensor could result in poor driveability complaints. - Intermittent Malfunctions