Powertrain Controls - ECM/PCM

Coolant Temperature Sensor Circuit Code 14:

Coolant Temperature Sensor Circuit:

Circuit Description:
The Coolant Temperature Sensor (CTS) is a thermistor that controls 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 (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. Code 14 will set if:

^ Signal voltage indicates a coolant temperature above 135°C (270°F) for 6 seconds.

2. This test simulates conditions for a code 15. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are OK.


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.