Powertrain Controls - ECM/PCM

Code 25 Chart:

Code 25 Wiring Diagram:

CIRCUIT DESCRIPTION
The Manifold Air Temperature (MAT) sensor is a thermistor. The Electronic Control Module (ECM) applies a voltage (about 5 volts) on circuit 472 to the sensor. When air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will measure a high signal voltage. If the air is warm, the sensor resistance is low, and the ECM will measure a low voltage.

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).
^ Vehicle speed is greater than 35 mph.
^ Both of the above requirements are met for at least 16 seconds.
^ Due to the conditions necessary to set a Code 25, the "Service Engine Soon" 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 185 ohms, replace the sensor.