P1114

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the VCM. The VCM applies a voltage on the 5 volt reference circuit to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore, the VCM senses a high signal voltage, and the VCM indicates the coolant temperature. As the engine warms, the sensor resistance becomes less and the voltage drops indicating the high coolant temperature. At the normal engine operating temperature (85°C to 95°C), the voltage measures about 1.5 to 2.0 volts. This DTC is a type D DTC.

CONDITIONS FOR SETTING THE DTC
The signal voltage indicates an engine coolant temperature voltage less than 0.82 volts and engine run time is greater than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The VCM stores the DTC to the history if the VCM detects an intermittent problem.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the Malfunction Indicator Lamp (MIL) off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

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

The scan tool displays the engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C then stabilize when the thermostat opens.

Use the Temperature vs. Resistance Value scale to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed or mis-scaled sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.

2. If the fault is still present, engine coolant voltage will be less than 0.82 volts.
3. This test simulates a DTC P0118. If the VCM recognizes the high signal voltage (high temperature), and the scan tool reads 4.9 volts or above, the VCM and wiring are OK.
4. This test will determine if the 5 volt reference circuit is open. There should be 5 volts present at sensor connector if measured with a J 39200. This will determine if there is a wiring problem or a faulty VCM.