P0118

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

DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit - High Input:

Engine Coolant Temperature (ECT) Sensor Circuit:

CIRCUIT DESCRIPTION
The engine coolant temperature sensor is a thermistor immersed in the intake manifold cooling system passage which is used to monitor the temperature of the engine coolant. The Vehicle Control Module-A (VCM-A) applies 5 volts to the sensor on CKT 410. When the coolant is cool, the resistance in the sensor will be high and the VCM-A will sense a high voltage signal. When the coolant is warm, the sensor resistance will be low and the VCM-A will sense a low voltage signal. DTC P0118 is a type "A" DTC.

DTC P0118 WILL SET WHEN
Engine running and Engine Coolant Temperature (ECT) signal voltage above 4.9 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 (l49°F) after 90 seconds has elapsed.

DTC P0118 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 present, engine coolant temperature voltage will be greater than 4.9V.
2. This test simulates conditions for a DTC P0117. If the VCM-A recognizes the grounded circuit (low voltage) and displays a low voltage, the VCM-A and wiring are OK.
3. This test checks for open or grounded signal sensor circuit. Also being checked are the ECT sensor ground circuit and the VCM-A.

DIAGNOSTIC AIDS
A faulty connection or an open in the 5 volt reference circuit or the sensor ground circuit will result in a DTC P0118.

The scan tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 9O°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.