Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 14:

Engine Coolant Temperature Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor 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 coolant is cold the sensor (thermistor) resistance is high, therefore the ECM will sense high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature (85°C - 95°C or 185°F - 203°F) the voltage will measure about 1.5 to 2.0 volts.

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 150°C (302°F) for 2 seconds with engine running.

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 scan tool displays engine temperature in degrees Celsius and Fahrenheit. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens.

Refer to Intermittents in Diagnosis By Symptom. Testing and Inspection