DTC 25

Fig. 036 Code 25 Manifold Air Temperature (MAT) Sensor Circuit:

Fig. 037 Code 25 Manifold Air Temperature (MAT) Sensor Circuit:

CIRCUIT DESCRIPTION:
The Manifold Air Temperature 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 see a high signal voltage. As the air warms, the sensor resistance becomes less and the voltage drops.

TEST DESCRIPTION: Numbers below refer to circled numbers on Diagnostic Charts.

1. This check determines if the Code 25 is the result of a hard failure or an intermittent condition.
A Code 25 will set if:
^ A MAT temperature greater than 135 degrees C is detected for a time longer than 2 seconds.

DIAGNOSTIC AIDS:

^ If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperatures may be checked with a "Scan" tool and should read close to each other.
^ A Code 25 will result if CKT 472 is shorted to ground.
^ If Code 25 is intermittent, refer to DIAGNOSIS BY SYMPTOM.