DTC 15

Code 15 "Coolant Temperature Sensor":

Wiring Diagram - Coolant Temperature Sensor:

CODE 15

COOLANT TEMPERATURE SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)


Circuit Description:

The coolant temperature sensor uses a thermistor to control the signal voltage at 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 180 F to 203 degrees F (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 15 will set if the O2 Signal voltage indicates a coolant temperature less than -10 degrees C (-30 F) for at least 5 minutes after start.

2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and the "Scan" displays above 130 degrees C, the ECM and wiring are OK.

3. This test will determine if CKT 410 is open. There should be 5 volts present at sensor connector if measured with a DVM.

Diagnostic Aids:

"Scan" tool displays engine temperature in degrees celsius. After engine is started, the temperature should rise steadily to about 90 degrees C, then stabilize when thermostat opens. An intermittent may be caused by a poor connection or a wire broken inside the insulation.


Check for:
Poor Connection or Damaged Harness - Inspect ECM harness connectors for backed out terminals "3" or "7", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness A faulty connection or an open in CKT 410 or 452 will result in a Code 15. Check terminals at sensor for good contact. Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.

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 - "Scan" coolant temperature should rise well above -1 degree C (30 F) within 5 minutes engine run time unless the sensor is shifted. 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.