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 38 indicates that the MAT sensor signal voltage is too high. This condition will be observed in engine data display as a "MAT" reading (parameter .0.5) of-40° to -35°C. Possible causes of this condition are:

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

If the opposite failure mode (shorted 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 148° to 151°C. To create a shorted sensor signal, disconnect the MAT sensor and jumper the harness terminals together. If the "MAT" reading is 148° to 151°C, the ECM and the wiring harness are OK. The fault must be in the sensor connector or MAT sensor itself
If the "MAT" reading is 147°C or less, then there is an open in the signal circuit 472, in the sensor ground circuit 476-Y, or in the ECM. If the "MAT" reading is now 148° to 151°C with circuit 472 jumpered to ground, an open exists in circuit 476-Y.
If the "MAT" reading remains 147°C or less with circuit 472 jumpered to ground at the ECM, either the ECM connector or ECM itself is faulty. If the reading is now 148° to 151°C an open exists in circuit 472.