DTC 14

Code 14 Diagnostic Chart:

TPS, CTS, & IAT Sensors (Circuit Diagram):

CIRCUIT DESCRIPTION:
The coolant temperature sensor uses a thermistor to control the signal voltage to the PCM. The PCM applies a reference voltage on CKT 410 to the sensor and then monitors the voltage in the circuit. When the engine is cold the sensor (thermistor) resistance is high, therefore, the PCM 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.

Code 14 will set if the following conditions exist.
^ Engine running for more than 10 seconds.
^ Voltage as measured at circuit 410 indicates temperature greater than 140°C (284°F).

If Code 14 is set, the PCM will use a default coolant temperature value of 48.5°C (119°C) for fuel control.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Checks to see if sensor circuit is indicating a high engine temperature to the PCM.
2. This test will determine if CKT 410 is shorted to ground (which will simulate the conditions for Code 14 - large drop in reference voltage at circuit 410.)

DIAGNOSTIC AIDS
^ "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, An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

^ Intermittent Test
If connections and harness check OK, "Scan" coolant temperature while moving related connectors and wiring harness. If the failure is induced, the "coolant temperature" display will change. This may help to isolate the location of the malfunction.

^ Shifted Sensor
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, which may result in driveability complaints.