DTC 25

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) on CKT 996 to the sensor. When manifold air is cold the sensor (Thermistor) resistance is high, therefore the Engine Control Module (ECM) will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.

Code 25 will set if:
^ Signal voltage indicates a manifold air temperature greater than 135°C (275°F) for 3 seconds.
^ Time since engine start is 8 minutes or longer.
^ A vehicle speed is present.

Due to the conditions necessary to set a Code 25 the check engine light will only remain on while the signal is low and vehicle speed is present.

CHART TEST DESCRIPTION
1. If voltage is above 4 volts, the ECM and wiring are OK.

2. If the resistance is less than 185 ohms replace the sensor.