Powertrain Controls - ECM/PCM

DTC 14 Engine Coolant Temperature Sensor Circuit:

Engine Coolant Temperature Sensor Wiring Diagram:

Circuit Description:

The Engine Coolant Temperature Sensor (ECT) uses a thermistor to control the signal voltage to the Engine Control Module (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 ECM terminal "A31"

Engine coolant temperature is one of the inputs used to control:

- Fuel delivery.
- EVAP canister purge.
- Ignition Control (IC).
- Exhaust Gas Recirculation (EGR).
- Idle Air Control (IAC).
- Cooling fan operation.
- Torque Converter Clutch (TCC).


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. DTC 14 will set if signal voltage indicates a coolant temperature above 135°C (270°F) for longer than 20 seconds.

2. This test will determine if CKT 410 is shorted to ground which will cause the conditions for DTC 14.

Diagnostic Aids:

Check harness routing for a potential short to ground in CKT 410.
Circuit is routed from the ECM to the 10-way INJ/ECM connector and then to the Engine Coolant Temperature (ECT) sensor.

The "Scan" tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C (194°F), then stabilize when thermostat opens.

Verify that engine is not overheating and has not been subjected to conditions which could create an overheating condition (i.e. overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.).

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, which may result in driveability complaints.