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 15 indicates that the coolant sensor signal voltage is too high. This condition will be observed in engine data display as a "coolant temperature" reading (parameter .0.4) of -40° to -35°C. Possible causes of this condition are:

A. An open coolant sensor.
B. Defective wiring, terminals, etc.
C. An ECM not processing the coolant 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 .0.4. With the opposite failure created, parameter .0.4 should display a "coolant temperature" reading of 148° to 151°C. To create a shorted sensor signal, disconnect the coolant sensor and jumper the harness terminals together. If the "coolant temperature" reading is 148° to 151°C, the ECM and the wiring harness are OK. The fault must be in the sensor connector or coolant sensor itself.
If the "coolant temperature" reading is 147°C or less, then there is an open in the signal circuit 410, in the sensor ground circuit 476-X, or in the ECM. If the "coolant temperature" reading is now 148° to 151°C with circuit 410 jumpered to ground, an open exists in circuit 476-X.
If the "coolant temperature" reading remains 147°C or less with circuit 410 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 410.