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 CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, therefore, ECM terminal "GE16" voltage will be high.

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 ECM terminal "GE16". Coolant temperature is one of the inputs used to control:

^ Fuel delivery
^ Engine Spark Timing (EST)
^ Idle Air Control (IAC)
^ Torque Convertor Clutch (TCC)
^ Controlled Canister Purge (CCP)
^ Cooling Fan

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to ECM CONNECTOR IDENTIFICATION under ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS for correct color code identification of circuit.

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

1. Code 15 will set if:

^ Signal voltage indicates a coolant temperature less than -39~C (-38~F) for 60 seconds.


2. This test simulates a Code 14. If the ECM senses the low signal voltage (high temperature) and the "Scan" reads 130~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:


^ A "Scan" tool displays engine temperature in degrees Celsius. After engine is started the temperature should rise steadily to about 95~C, and then stabilize when thermostat opens.

^ A faulty connection, or an open in CKT 410 or CKT 452 can result in a Code 15. Codes 15, 21 and 66 stored at the same time could be the result of an open CKT 452.

^ The "Temperature to Resistance Value" scale in the chart may be used to test the coolant sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.

^ Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.