Code EO37, Manifold Air Temperature (Mat) Sensor Too High: Notes

WARNING: This page is about a different car, the 1986 Oldsmobile Toronado and 1986 Buick Riviera. However, it is still accessible from the selected car via links, so may be relevant.

The MAT sensor measures the air temperature in the air cleaner box and relays this information to the ECM. The ECM applies and monitors a 5-volt signal to the sensor. The sensor is a thermistor that changes its internal resistance as its temperature changes.

When the sensor is cold (internal resistance high), the ECM will see a high signal voltage. This the ECM relates to a cold engine. As the sensor warms (internal resistance decreases), the voltage signal will decrease and the ECM will relate the lower voltage to a warm engine.

As the intake air temperature increases, the sensor resistance becomes less, and the voltage drops.

Code EO37 will set if a signal voltage indicates manifold air temperature about 275°F (135°C), and the vehicle is traveling over 40 MPH for over 16 seconds. Possible causes of a Code EO37 are: Faulty wiring or terminals, circuit 472 shorted to ground, shorted MAT sensor, or a faulty ECM.

Manifold air temperature is one of the inputs used to control: Fuel delivery, spark timing (EST), knock control (ESC), and idle speed (IAC).

If the opposite failure mode (open sensor) is created, then the self-diagnostics can be used to detect this failure by displaying engine data parameter ED05. With the opposite failure created, parameter ED05 should display a "MAT" reading of -35 to -40°C. To create an open sensor signal, disconnect the MAT sensor connector. If the "MAT" reading is now -35° to -40°C, the ECM and the wiring harness are okay. The fault must be in the MAT sensor itself.
If the "MAT" reading is -34°C or warmer, then there is a short to ground in the wiring harness or the ECM.