DTC 14

Code 14 Chart:

Code 14 Wiring Diagram:

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 the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "C16".

Coolant temperature is one of the inputs used to control:

^ Fuel delivery
^ Engine spark timing (EST)
^ Idle (IAC)
^ Converter clutch (TCC)
^ Canister purge (CCP)
^ EGR
^ Cooling fan

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION for correct color code identification of circuit.
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 (270~F).
^ Engine running longer than 20 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. CKT is routed from the ECM to a mini harness, and then to the coolant temperature sensor.


^ "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 TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.

^ Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.). The "Temperature To Resistance Value" scale may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.