DTC 25

Code 25 - Manifold Air Temp. (MAT) Sensor:

Wiring Diagram for Manifold Air Temp. (MAT) Sensor:

CODE 25 - MANIFOLD AIR TEMPERATURE SENSOR CIRCUIT (MAT) HIGH TEMPERATURE INDICATED

Circuit Description:


The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal-voltage to the ECM. The ECM applies a voltage (4-6) 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.

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


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 135~C (275~F) for 3 seconds

^ Time since engine start is 8 minutes or longer

^ A vehicle speed is present


If voltage is above 4 volts, the ECM and wiring are OK.

If the resistance is less than 185 ohms, replace the sensor.