DTC 15

Code 15 Chart:

Sensor Wiring Circuits:

CIRCUIT DESCRIPTION
The coolant temperature sensor uses a thermistor to control the signal voltage to the PCM. The PCM applies 5 volts on CKT 410 to the sensor. 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 at the PCM.

Code 15 will set if:
^ Engine run time over 2 seconds.
^ Signal voltage indicates a coolant temperature less than -39°C (-38°F) for at least .4 seconds.

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

1. Determines if the conditions exist for setting a Code 15.

2. This test simulates a Code 14. If the PCM recognizes the low signal voltage, (high temperature) and the "Scan" reads 130°C (266°F) or more, the PCM 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 reads engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 90°C (194°F) 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 PCM harness connectors for backed out terminal "R13" improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

^ Intermittent Test If connections and harness check OK, Scan coolant temperature while moving related connectors and wiring harness. If the failure is induced, the 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 CKTs 410 or 452 will result in a Code 15.