Powertrain Controls - ECM/PCM

Trouble Code 25 Chart:

Intake Air Temperature Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Intake Air Temperature (IAT) sensor is a thermistor that controls a signal voltage to the Powertrain Control Module (PCM). The PCM applies approximately 5 volts to the sensor on circuit 472. When the intake air is cold, the sensor resistance is high, therefore the voltage sensed at the input "C29" is high. If the air is warm, the sensor resistance will be low, and the voltage input to the PCM will be low.

DIAGNOSTIC TROUBLE CODE (DTC) 25 WILL SET WHEN
Vehicle speed is greater than 1 mph and intake air temperature indicates 145° C (297° F) for 5 seconds.

ACTION TAKEN (PCM) WILL DEFAULT TO
The PCM will use an IAT default value of 37° C (108° F) and the Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 25 WILL CLEAR WHEN
A current DTC 25 will clear when the intake air temperature is indicated below the high temperature threshold. A History DTC 25 will clear after 50 consecutive ignition key cycles without a current DTC 25 being stored.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This test is a verification that the DTC is not intermittent.
2. This test helps determine between a circuit fault and a faulty sensor.

DIAGNOSTIC AIDS
A Tech 1 scan tool reads the temperature of the air entering the engine and should read close to ambient air temperature when engine is cold. IAT values will rises as underhood temperature increases.
A short to ground in circuit 472 will result in a DTC 25.
The "Temperature to Resistance Values" scale in the chart may be used to test the IAT sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.
Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions