Diagnostic Aids

NOTE: If this code IS NOT displayed during the third pass of diagnostic codes, it is an intermittent failure and cannot be diagnosed using this procedure. For an intermittent code, refer to NOTE ON INTERMITTENTS.

Trouble Code 37 indicates that the MAT sensor signal voltage is too low. This condition will be observed in engine data display as a "MAT" reading (parameter .0.5) of 142° to 151°C. Possible causes of this condition are:

A. A shorted MAT sensor.
B. Defective wiring, terminals, etc.
C. ECM not processing the MAT signal properly.

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 .0.5. With the opposite failure created, parameter .0.5 should display a "MAT" reading of -40° to -35°C. To create an open sensor signal, disconnect the MAT sensor connector. If the "MAT" reading is now -40° to -35°C the ECM and the wiring harness are OK. The fault must be in the MAT sensor itself.
If the "MAT" reading is -34°C or greater, then there is a short to ground in the wiring harness or the ECM.