DTC 15

Code 15 Chart:

Code 15 Wiring Diagram:

CIRCUIT DESCRIPTION:

The coolant temperature sensor uses a thermistor to control the signal voltage to 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 the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "C16".

Coolant temperature is one of the inputs used to control:


^ Fuel delivery
^ Engine spark timing (EST)
^ Idle (IAC)
^ Converter clutch (TCC)
^ Canister purge (CCP)
^ EGR
^ Cooling fan

NOTE: Because of all the possible color code combinations used on electrical wiring diagrams, always refer to SCHEMATIC DIAGRAMS/ELECTRICAL AND ELECTRONIC WIRING DIAGRAMS/ECM CONNECTOR IDENTIFICATION 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 -38.5~C (-37.3~F).

2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and the "Scan" reads 130~C (266~F), 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 reads engine temperature in degrees centigrade. After engine is started the temperature should rise steadily to about 95~C (203~F) then stabilize when thermostat opens. CKT 410 is routed from the ECM to a mini harness, and then to the coolant temperature sensor.

^ A faulty connection, or an open in CKT 410 or 808 will result in a Code 15.

^ Codes 15 and 21 stored at the same time could be the result of an open CKT 808 which would also turn the temperature warning indicator "ON". 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. A "shifted" sensor could result in poor driveability complaints. Refer to TESTING PROCEDURES/DIAGNOSIS BY SYMPTOM/INTERMITTENTS.