DTC 15

Chart - Code 15 Coolant Sensor Circuit (Signal Voltage High):

Wiring Diagram for Coolant Sensor Circuit.:

CODE 15 - COOLANT TEMPERATURE SENSOR CIRCUIT (LOW TEMPERATURE INDICATED)


Circuit Description:
The Coolant Temperature Sensor uses a thermistor to control the signal voltage to the Electronic Control Module (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 to 95 Degrees C) the voltage will measure about 1.5 to 2.0 volts at the ECM.



Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. Code 15 will set if the signal voltage indicates a coolant temperature less than -44 Degrees C (-47 Degrees F) for at least 3 seconds.
2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temp.) and the "Scan" reads 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 Digital Volt Meter (DVOM).

Diagnostic Aids:

A "Scan" tool reads engine temperature in degrees centigrade. 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, rubbed through wire insulation or a wire broken inside the insulation.


Check For:
Poor Connection or Damaged Harness Inspect ECM harness connectors for backed out terminals "C1O" or "D12", improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Intermittent Test If connections and harness checks out 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.

A faulty connection, or an open in CKT 410 or 452 will result in a Code 15. If Code 23 or 63 is also set, check CKT 452 for faulty wiring or connections. Check terminals at sensor for good contact. Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.