CODE 25: MAT SENSOR CKT-HIGH TEMP INDICATED (TURBO)
The MAT sensor uses a thermistor to control signal voltage to the ECM. The ECM applies 4-6 volts on Blue/Black wire to MAT sensor. When manifold air is cold, sensor resistance is high and ECM will see a high voltage. As air temperature increases, sensor resistance decreases and the voltage drops.
Note. Test numbers refer to test numbers on diagnostic chart.
- This determines if Code 25 is the result of a hard failure or an intermittent condition. Code 25 will set if MAT temperature is greater than 293°F (145°C) for more than 2 minutes.
If engine is allowed to cool overnight, coolant temperature and Manifold Air Temperature (MAT) should read nearly the same with Scan tester. A Code 25 results if Blue/Black wire or Black/White wire becomes open or shorted to ground. For intermittent inspection, see INTERMITTENTS in H - EFI TESTS W/O CODES article in the ENGINE PERFORMANCE Section.
| Temp. °F(°C) | Ohms |
|---|---|
| 210(100) | 185 |
| 160(70) | 450 |
| 100(38) | 1800 |
| 70(20) | 3400 |
| 40(4) | 7500 |
| 20(-7) | 13,500 |
| 0(-18) | 25,000 |
| 40(-40) | 100,700 |
MAT SENSOR RESISTANCE
