DTC 25

Code 25 - Manifold Air Temperature (MAT) Sensor Circuit:

Wiring Diagram For Code 25 - Manifold Air Temperature (MAT) Sensor Circuit:

CODE 25 - MANIFOLD AIR TEMPERATURE (MAT) SENSOR CIRCUIT

Circuit Description:

The Manifold Air Temperature (MAT) Sensor is a thermistor that controls the signal voltage to the ECM.

The ECM applies a voltage (4-6 volts) on CKT 472 to the sensor. When the 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 above 150~C (302~F) for 2 seconds.
^ Time since engine start is 1 minute 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.

Check harness routing for possible short to ground in CKT 472.

See Diagnosis By Symptoms - No Trouble Codes Stored.

The "Temperature to Resistance Value" scale at the right may be used to test the MAT sensor at various temperature levels to evaluate the possibility of a "slewed" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.