DTC 14

Flowchart Code 14:

Coolant Temperature Sensor Circuit:

CIRCUIT DESCRIPTION
The coolant temperature sensor uses a thermistor to control the signal voltage to the Electronic Control Module (ECM). The ECM applies a voltage on Circuit (CKT) 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature (85°C to 95°C), the voltage will measure about 1.5 to 2.0 volts.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Code 14 will set if Signal voltage indicates a coolant temperature above 135°C (275°F) for 3 seconds.

2. This test will determine if CKT 410 is shorted to ground which will cause the conditions for Code 14.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground in CKT 410. "Scan" tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C, then stabilize when thermostat opens. Refer to Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions