P0117

***This article was updated by TSB 51-65-66***

DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit - Low Input:

Engine Coolant Temperature (ECT) Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the Vehicle Control Module-A (VCM-A). The VCM-A applies a voltage on CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore, the VCM-A will sense a high signal voltage and coolant temperature will be indicated.

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 (185°F to 203°F), the voltage will measure about 1.5 to 2.0 volts. DTC P0117 is a type "A" DTC.

DTC PO117 WILL SET WHEN
Engine running and ECT signal voltage is less than 0.82 volts for 5 seconds.

ACTION TAKEN (VCM-A WILL DEFAULT TO)
Malfunction Indicator Lamp (MIL) will be turned "ON" by the VCM-A. Coolant temperature will default to 0°C (32°F) for the first 90 seconds on a cold engine and then to 65°C (149°F) after 90 seconds has elapsed.

DTC PO117 WILL CLEAR WHEN
The VCM-A will turn the MIL "OFF" after three consecutive trips without a fault condition present. A history DTC will be cleared if no fault conditions have been detected for forty warm-up cycles [coolant temperature has risen 22°C (40°F) from start-up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle] or the Tech 1 clearing feature has been used.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. If the fault is still present, engine coolant voltage will be less than 0.82V.
2. This test simulates a DTC P0118. If the VCM-A recognizes the high signal voltage and the Tech 1 scan reads 40V or above, the VCM-A and wiring are OK.
3. This test will determine if CKT 410 is open. There should be 5 volts present at sensor connector if measured with J 39200. This will determine if there is a wiring problem or a faulty VCM-A.

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

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

The "Temperature vs. Resistance Value" scale at the bottom of the diagnostic chart may be used to test the 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.