DTC 25

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

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

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

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 (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. If the air warms, the sensor resistance becomes less, and the voltage drops.

The MAT Sensor is part of the Mass Air Flow (MAF) Sensor assembly so the ECM can accurately compensate air flow readings based on temperature.


Test Description: Numbers below refer to circled numbers on the diagnostic chart. Code 25 will set if:

^ Signal voltage indicates a manifold air temperature greater than 135~C (275~F).

^ A vehicle speed is present.

^ Both of the above requirements are met for at least 30 seconds.

Due to the conditions necessary to set a Code 25, the "Service Engine Soon" (SES) light will only stay "ON" while the fault is present.


1. A "Scan" tool may not be used to diagnose this fault, due to the ECM transmitting "default" (substitute) values, when the fault is present. If voltage is above 4 volts, the ECM and wiring are OK.


2. If the resistance is less than 100 ohms, replace the sensor.