Action Taken

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on SERVICE SOON light.
ECM uses MAT sensor value in place of coolant sensor value for all calculations.

The coolant sensor is a thermistor (temperature-sensitive resistor). Sensor uses a 2-wire harness. Sensor signal voltage comes from ECM to terminal "B" on circuit No. 410. Sensor reference ground comes to terminal "A" from ECM on circuit No. 476.

As temperature of sensor increases, sensor resistance is lower. The monitored signal voltage from ECM to terminal "B" decreases as sensor temperature increases and current flows through the sensor element to terminal "A" sensor ground.

Code E14 sets because ECM assumes that coolant temperature cannot be 291°F (144°C) or greater when MAT is 212°F (100°C) or less (sensor signal shorted to ground).

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) With sensor or wiring shorted, parameter P.0.4 should read 298°F (148°C) or greater. If not, the sensor is not shorted. See Note on Intermittents.

Test Number 2) Check for sensor shorted or circuit No. 410 shorted. If parameter stays at 288°F (142°C) or greater with sensor unplugged, the short is in circuit No. 410 between sensor and ECM.

Test Number 3) Fault is most likely at ECM connector or ECM. Before ECM is replaced, perform CHART C-1: ECM REPLACEMENT CHECK .