Powertrain Controls - ECM/PCM

DTC 14 Engine Coolant Temperature Sensor Circuit (High Temp):

Engine Coolant Temperature (ECT) Sensor Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the PCM. The Powertrain Control Module (PCM) applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore the PCM will see high signal voltage.
As the engine warms the sensor resistance becomes less and the voltage drops. At normal engine operating temperature 88 to 106°C (190 to 222°F) the voltage will measure about 0.5 to 1.1 volts.

DIAGNOSTIC TROUBLE CODE (DTC) 14 WILL SET WHEN
The signal voltage indicates engine coolant temperature is above 135°C (275°F). Engine must be running longer than 6 seconds before this test will begin.

ACTION TAKEN (PCM will default to)
The PCM will use a default value of 87°C (189°F) for fuel delivery calculations. The cooling fans will be enabled and the MIL will become illuminated.

DTC 14 WILL CLEAR WHEN
The failure is no longer detected [temperature falls below 135°C (275°F) threshold]. A history DTC will clear after 50 consecutive key cycles without a current DTC 14 being stored.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This check is to determine if 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 temperature in degrees centigrade and degrees fahrenheit. After engine is started, the temperature should rise steadily between 88-106°C (190-222°F) then stabilize when thermostat opens. The cooling fan should turn "ON" at 106°C (222°F).

Refer to Intermittents under Computers and Control Systems/System Diagnosis/Diagnosis By Symptom. - Intermittent Malfunctions