Engine Control Module ECM

Diagnostic Trouble Code 14:

ECT Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the ECM. The ECM applies a voltage on 5 volt reference circuit to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore the ECM will see a high signal voltage.

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

DTC 14 WILL SET WHEN
Signal voltage indicates a coolant temperature above 135°C (270°F) while engine not running or coolant temperature is above 135°C (270°F) while engine running less than 90 seconds.

ACTION TAKEN (ECM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate.

DTC 14 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

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

1. Checks to see if DTC was set as result of a hard failure or intermittent condition.

2. This test simulates conditions for DTC 15. If the ECM recognizes the open circuit (high voltage) and displays a low temperature, the ECM and wiring are OK.

DIAGNOSTIC AIDS
Check harness routing for a potential short to ground in 5 volt reference circuit.

Tech 1 scan tool displays engine coolant temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens. A faulty connection or an open in the 5 volt reference circuit will result in a DTC 14.

Refer to Diagnosis By Symptom / Intermittents - Intermittent Malfunctions

The "Temperature to Resistance Value" scale in the chart may be used to test the engine coolant sensor at various temperature levels to evaluate the possibility of a "skewed" (mis-scaled) sensor. A "skewed" sensor could result in poor driveability complaints.