Powertrain Controls - ECM/PCM

Code Chart 25:

Intake Air Temperature Sensor (IAT) Wiring Diagram:

CIRCUIT DESCRIPTION:
The Manifold Air Temperature (MAT) Sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage (about 5 volts) on CKT 472 to the sensor. When manifold 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.

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

1. Code 25 will set if:

^ Signal voltage indicates a manifold air temperature greater than 145°C (293°F) for 3 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 Code 23. - Intermittent Malfunctions