P0117

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 voltage signal, and the VCM indicates a low coolant temperature. As the engine warms, the sensor resistance becomes less and the voltage drops indicating high coolant temperature. At normal engine operating temperature (85°C to 95°C), the voltage measures about 1.5 to 2.0 volts. This DTC is a type A DTC.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

^ The engine is running.
^ Signal voltage is less than 0.78 volts for 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
The VCM sets the DTC P0117. The VCM turns on the Malfunction Indicator Lamp (MIL) when P0117 is reported and 1 failure has occurred.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the 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 16O°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS
The scan tool displays engine temperature in degrees centigrade. After starting the engine, the temperature should rise steadily to about 90°C then stabilize when the thermostat opens. A faulty connection or an open in the 5 volt reference circuit or the sensor ground circuit results in a DTC P0117.

Use the Temperature vs. Resistance Value Table to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed (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, the engine coolant voltage will measure less than 0.82 volts.
3. This test simulates a DTC P0118. If the VCM recognizes the high signal voltage and the scan tool display reads 40 volts or more, the VCM and the wiring are okay.