DTC 25

Intake Air Temperature Sensor Circuit:

Circuit Description:
The Intake Air Temperature (IAT) sensor is a thermistor. The PCM applies a voltage (about 5 volts) on CKT 472 to the sensor. When air is cold, the sensor resistance is high and the PCM will measure a high signal voltage. If the air is warm, the sensor resistance is low causing the PCM to measure a low voltage.

Code 25 will set if:

^ Signal voltage indicates an intake air temperature greater than 103°C (215°F).
^ Vehicle speed is greater than 35 mph.
^ Both of the above requirements are met for at least 5 seconds.

Code 25 does not illuminate the "Service Engine Soon" light.

Code 25 Diagnostic Chart:

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

1. A Tech 1 may be used to diagnose this fault since the PCM transmits "actual" values when the fault is present. A grounded circuit will cause the Tech 1 to display a temperature of approximately 147°C (297°F).

2. If the Tech 1 displays 400 with the IAT sensor disconnected, the PCM and wiring are OK and the IAT sensor must be replaced.


Diagnostic Aids:
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Check for:

^ Poor Connection or Damaged Harness - Inspect PCM harness for short to ground in CKT 472, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

^ Intermittent Test - Observe Intake Air Temperature (IAT) on Tech 1 while moving related connectors and wiring harness with warm engine running. If the failure is induced, the IAT display will change to a 147°C (297°F) temperature reading. This may help to isolate the location of the malfunction.