With PFI

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

Wiring Diagram for Manifold Air Temperature Sensor Circuit:

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 degrees C (275 degrees F).
The above requirement is 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, while 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.