Code 14 - Coolant Temperature Sensor Circuit (High temperature indicated)

Circuit Description

The coolant temperature sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage on 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.

Problem Description:

Code 14 will set if:

Signal voltage indicates a coolant temperature above 135 C (275 F) for 3 seconds.
Engine running longer than 20 seconds.

Diagnostic Aids:

Check harness routing for a potential short to ground in CKT 410.

Scantool displays engine temp in degrees centigrade. After engine is started, the temperature should rise steadily to about 90 C, then stabilize when the thermostat opens.

"Scan" Diagnostics:

Does scantool display 130 C or hotter?

NO YES