Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code 25, Mat Sensor Temp. High - 1991 2.5L & 4.3L Turbo: Notes
| Application | ECM Terminal | Wire Color | |
|---|---|---|---|
| 2.5L | |||
| Signal | C12 | Tan | |
| MAT Ground | D2 | Black/Red | |
| 4.3L Turbo | |||
| Signal | GF16 | Tan | |
| MAT Ground | BB5 | Black/Red | |
The ECM applies and monitors a voltage signal (4-6 volts) to MAT sensor. When manifold air is cold, the sensor resistance is high and ECM sees a high signal voltage. As air warms, resistance decreases and voltage sensed by the ECM drops. Sensor resistance can be measured at sensor terminals with harness disconnected.
- This checks if the code is a hard failure or an intermittent condition. Code 25 will set if a MAT temperature greater than 266°F (130°C) is sensed for more than a precalibrated period.
- This simulates condition for code 23. If control module recognizes the open circuit and "Scan" tester displays a temperature of less than -30°C, control module and wiring are okay.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.