With PFI

Code 25 Chart:

Code 25 Wiring Diagram:

CIRCUIT DESCRIPTION:

The Manifold Air Temperature (MAT) Sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage (about 5 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.

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.



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 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 the ECM transmitting "default" (substitute) values while the fault is present. If voltage is above 4 volts the wiring and ECM are OK.

2. If resistance is below 100 ohms, replace the sensor.