Powertrain Controls - ECM/PCM

Code 14 - Coolant Temperature Sensor Circuit:

Wiring Diagram For Code 14 - Coolant Temperature Sensor Circuit:

CODE 14 - COOLANT TEMPERATURE SENSOR CIRCUIT



CIRCUIT DESCRIPTION:

The coolant temperature sensor is a thermistor that controls 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.



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

1. Checks to see if code was set as a result of a hard failure or intermittent problem.

Code 14 will set if:

^ Signal voltage indicates a coolant temperature above 130~C (266~F) for 6 seconds.

2. This test stimulates conditions for a code 14. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are ok.


DIAGNOSTIC AIDS:

Check harness routing for a potential short to ground in CKT 410.
"Scan" tool displays engine temp. in degrees centigrade. After engine is started, the temperature should rise steadily to about 90~C then stabilize when thermostat opens.

The "Temperature to Resistance Value" scale above can be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "slewed" (mis-scaled) sensor. A "slewed" sensor could result in poor driveability complaints.

SEE DIAGNOSIS BY SYMPTOM - NO TROUBLE CODES STORED.