Powertrain Controls - ECM/PCM

DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit (High Temperature Indicated):

ECT Sensor Wiring Circuit:

Circuit Description:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage from the Powertrain Control Module (PCM). The PCM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore PCM terminal "PC10" voltage will be high.

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 PCM terminal "PC10".

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 solenoid
^ Electric cooling fans.

DTC 14 Will Set When:
^ Signal voltage indicates the engine coolant temperature is greater than 140°C (285°F).
^ The engine is running for greater than 128 seconds.

Action Taken (PCM will default to): The Malfunction indicator Lamp (MIL) will illuminate, the PCM will default to 85°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 checks to see 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 DTC 14.

Diagnostic Aids: Check harness routing for a potential short to ground in CKT 410. A Tech 1 scan tool displays engine coolant temperature in degrees Celsius. After engine is started, the temperature should rise steadily to about 90°C, and then stabilize when thermostat opens. Refer to "Intermittents," in "Diagnosis By Symptom." - Intermittent Malfunctions

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. A shifted sensor could result in poor driveability.