DTC 25

DTC 23 Circuit Diagram:

DTC 25 Diagnostic Chart High Temp Indicated In MAT Circuit:

CIRCUIT DESCRIPTION:

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6V) on BLU/BLK wire 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: The numbers below refer to circled numbers on the diagnostic chart.

1. This step checks to see if Code 25 is the result of a hard failure or an intermittent condition. A Code 25 will set if:

^ An MAT temperature greater than 145°C is detected for a time longer than 120 seconds.

DIAGNOSTIC AIDS:

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and IAT temperatures may be checked with a Scan tool and should read close to each other. A Code 25 will result if BLU/BLK wire become shorted to ground or open. If Code 25 is intermittent,
Intermittant Check Procedure