DTC 25

Chart - Code 25 Manifold Air Temperature (Signal Voltage Low):

Wiring Diagram for Manifold Air Temperature 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.


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 degrees 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.