Powertrain Controls - ECM/PCM

DTC 14 Chart:

Engine Coolant Temperature Sensor Circuit:

Circuit Description:
The Engine Coolant Temperature (ECT) sensor is a thermistor which varies the signal voltage at the PCM. The PCM applies 5 volts to sensor on CKT 410. The sensor's resistance is inversely proportional to the temperature it is sensing.

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 PCM terminal "A31."

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

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

DTC 14 Will Set When:
The signal voltage indicates engine coolant temperature is greater than 135°C (275°F). Engine must be running for greater than 20 seconds before this test will begin.

Action Taken (PCM will default to):
The PCM will use a default value of 90°C (194°F) for fuel delivery calculations. The cooling fans will be enabled and the MIL will become illuminated.

DTC 14 Will Clear When:
Current DTC 14 will clear when the failure is no longer detected (temperature falls below 135°C (275°F) threshold). A history DTC 14 will clear after 50 consecutive ignition key cycles without a current DTC 14 being stored.

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

1. This check is to determine if a DTC 14 is intermittent or a current malfunction.

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. This circuit is routed from the PCM to the 10-way INJ/PCM connector, and then to the ECT sensor.

Tech 1 scan tool displays engine coolant temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens. Refer to "Intermittents" in "Diagnosis By Symptom." - Intermittent Malfunctions

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 at the right may be used to test the engine coolant temperature sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor. A "shifted" sensor could result in poor driveability complaints.