Powertrain Controls - ECM/PCM

Trouble Code 14 Chart:

Engine Coolant Temperature Sensor Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor used to modulate a 5 volt reference signal applied to CKT 410. When the engine is cold, the sensor resistance is high which causes the voltage at pin "A31" to remain high. The PCM calculates a high signal voltage as a low engine coolant temperature.

As the engine warms, the sensor resistance drops and voltage at the PCM terminal drops. At normal engine operating temperature, the voltage will measure approximately 1.75 volts on CKT 410.

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

^ Fuel delivery.
^ Idle air control.
^ Purge control.
^ Cooling fan operation
^ Ignition control.
^ TCC operation.
^ EGR operation.

DTC 14 Will Set When: The signal voltage indicates engine coolant temperature is greater than 135°C (275°F) for one second. Engine must be running for greater than 10 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.
^ 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 in "Diagnosis by Symptoms". Testing and Inspection
^ 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 in the chart 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.