DTC 15

Code 15 Chart:

Code 15 Wiring Diagram:

CIRCUIT DESCRIPTION:

The coolant temperature sensor uses a thermistor to control the signal voltage at the ECM. The ECM applies a voltage on circuit 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the ECM will see a 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

Code 15 will set if:

^ Engine running.

^ Signal voltage indicates a coolant temperature less than 138~C (-38~F) for 0.4 seconds.


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

1. This will determine if the coolant sensor is indicating a low temperature to the ECM.

2. This test simulates a Code 14. If the ECM senses the low signal voltage (high temperature) and the "Scan" reads 140~C, the ECM and wiring are OK.

3. This test will determine if circuit 410 is open. There should be 5 volts present at sensor connector if measured with a DVM. If Code 15 is set, the ECM will use 49~C (120~F) for fuel control. "Scan" tool will display actual value.


DIAGNOSTIC AIDS:

^ "Scan" tool displays engine temperature in degrees Celsius. After engine is started, the temperature should rise steadily to about 90~C, and 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 terminal "YE16", 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 "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 circuits 410 or 452 will result in a Code 15. If a code 23 is also set, check circuit 452 for faulty wiring or connections. Refer to intermittents.