Powertrain Controls - ECM/PCM

DTC 15 Chart (generic):

ECT Circuit (Typical):

Circuit Description:
The Coolant Temperature Sensor (CTS) is a thermistor that controls the signal voltage to the control module. The control module applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high, therefore the control module 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.

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

1. Checks to see if code was set as result of a hard failure or intermittent condition.

Code 15 will set if:
^ Signal voltage indicates a coolant temperature less than -33°C (-27°F) for 30 seconds.

2. This test simulates conditions for a code 14. If the control module recognizes the low signal voltage (high temperature), and the Tech 1 "SCAN" reads 130°C (266°F) or above, the control module 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 DVOM. This will determine if there is a wiring problem or a faulty control module.


Diagnostic Aids:
Check harness routing for a potential short to ground in CKT 410.

Tech 1 "Scan" tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C then stabilize when thermostat opens.

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