Powertrain Controls - ECM/PCM

DTC 14 Chart:

Engine Coolant Temperature (ECT) Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM supplies a 5 volt reference and a ground to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore PCM terminal voltage will be high.
As the engine warms, the sensor resistance decreases, and the voltage drops. At normal engine operating temperature, ECT sensor voltage should be between 1.5 to 2.0 volts.

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

^ Fuel delivery.
^ Ignition Control (IC).
^ Idle Air Control (IAC).
^ Torque Convertor Clutch (TCC).
^ Evaporative (EVAP) canister purge valve.
^ Electric cooling fan.

DIAGNOSTIC TROUBLE CODE (DTC) 14 WILL SET WHEN
^ The signal voltage indicates engine coolant temperature is greater than 140°C (285°F).
^ The engine run time is greater than 128 seconds.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, the PCM will default to 92°C for engine coolant temperature (Tech 1 scan tool will not show defaulted value), and the cooling fan will enable.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step checks if DTC 14 was set as a result of a hard failure or intermittent condition.
2. This test will determine if CKT 410 is shorted to ground which will cause the conditions for a DTC 14 to set.

DIAGNOSTIC AIDS
^ After engine is started, the temperature should rise steadily to about 90°C, and then stabilize when thermostat opens.
^ Verify the 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 vs. Resistance Value" scale at the right may be used to test the sensor at various temperature levels to evaluate the possibility of a shifted (mis-scaled) sensor.
^ Refer to "Intermittents," in Diagnosis by Symptom. - Intermittent Malfunctions