Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6 volts) on CKT 472 to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore the ECM will detect 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 the engine is not experiencing turbocharger boost and the following conditions are met:
^ Signal voltage indicates a manifold air temperature greater than 135°C (275°F).
^ The above requirement is met for at least 30 seconds.
Due to the conditions necessary to set a Code 25, the "Check Engine" 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.