P0118

DTC P0118 Engine Coolant Temperature (ECT) Sensor Diagnostic Chart:

Engine Coolant Temperature (ECT) Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal voltage to the Powertrain Control Module (PCM). The PCM applies a voltage on CKT 410 to the sensor. When the engine is cold the sensor (thermistor) resistance is high, therefore, the PCM will see high signal voltage.

As the engine warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature 85°C to 95°C (185°F to 203°F) the signal will measure about 1.5 to 2.0 volts.


DIAGNOSTIC TROUBLE CODE (DTC) PO118 WILL SET WHEN
^ Engine run time is greater than 3 seconds.
^ Signal voltage indicates engine coolant temperature above 140°C (284°F) for 0.4 second.

ACTION TAKEN (PCM WILL DEFAULT TO)
With a current DTC P0118 set, the PCM will turn the high speed cooling fans "ON" and use a default engine coolant temperature value based on run time. The default value will rise to a maximum value of 90°C (194°F). The PCM will illuminate the Malfunction Indicator Lamp (MIL).

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Determines if conditions necessary to set DTC P0118 exist.
2. This test will determine if CKT 410 is shorted to ground.

DIAGNOSTIC AIDS
Tech 1 scan tool displays engine coolant temperature in degrees. After engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when thermostat opens.
An intermittent may be caused by rubbed through wire insulation.

Check for:
^ CKT 410 shorted to ground.
^ Intermittent test - With scan tool, monitor engine coolant temperature while moving related connectors and wiring harness. If the failure is induced, the engine coolant temperature display will change. This may help to isolate the location of the malfunction.
^ Shifted sensor - The "Temperature To Resistance Value" scale in the diagnostic chart may be used to test the engine coolant temperature sensor at various temperature levels to evaluate the possibility of a "shifted" (mis-scaled) sensor, which may result in driveability complaints.