P0118

DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temperature Indicated):

Engine Coolant Temperature (ECT) Sensor Circuit:

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 CKT 410 to the sensor. When the engine is cold, the sensor (thermistor) resistance is high; therefore, the VCM will sense a high signal voltage and low 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), the voltage will measure about 1.5 to 2.0 volts.

DTC P0118 Will Set When
Signal voltage indicates an engine coolant temperature above 135°C (270°F) and engine run time is greater than 3 seconds.

Action Taken (VCM will default to)
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 P0118 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 Fuse #9 (ECM B) fuse is removed for 10 seconds.

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 will be greater than 135°C (275°F).

2. This test simulates conditions for a DTC P0117. If the VCM recognizes the open circuit (high voltage) and displays a low temperature, the VCM and wiring are OK.

Diagnostic Aids
Check harness routing for a potential short to ground in CKT 410.

Tech 1 scan tool displays engine temperature in degrees centigrade. After engine is started, the temperature should rise steadily to about 90°C then stabilize when thermostat opens. Refer to "Intermittents". - Intermittent Malfunctions

The "Temperature to Resistance Value" scale at the right 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.