DTC 15

Coolant Temperature Sensor Circuit:

Circuit Description
The Coolant Temperature Sensor (CTS) 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 88 to 106°C (190 to 222°F) the voltage will measure about .5 to 1.1 volts at the ECM.

Code 15 Diagnostic Chart:

Test Description
Number(s) below refer to circled number(s) on the diagnostic chart

1. Code 15 will set if:
^ Engine running longer than 30 seconds.
^ Coolant temperature less than -33°C (-27°F).

2. This test simulates a Code 14. If the ECM recognizes the low signal voltage, (high temperature) and Tech 1 "Scan" tool reads 130°C or above, 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 Tech 1 "Scan" tool reads engine temperature in degrees centigrade and degrees fahrenheit. After engine is started the temperature should rise steadily between 88°C (106°F) then stabilize when thermostat opens. The fan will turn "ON" at 106°C (222°F).

If Code 21 is also set, check CKT 452 for fault, wiring or connections. Check terminals at sensor for good contact. - Intermittent Malfunctions