CODE P0118, COOLANT TEMP. SENSOR HIGH TEMPERATURE INDICATED Chevrolet Lumina I

CODE P0118, COOLANT TEMP. SENSOR HIGH TEMPERATURE INDICATED

ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5-volt reference signal to sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms, sensor resistance becomes less and PCM voltage drops. With Code P0118 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set code exist.
2. This test will determine if signal circuit is shorted to ground which will cause conditions for Code P0118.
3. This test will determine if sensor circuits are open. If circuits are okay, check connections at PCM and ECT sensor.

Tech 1 displays engine temperature in degrees Celsius (°C). After engine is started, temperature should rise steadily to about 90°C, then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check the following for

1. A short to ground in coolant sensor signal circuit.
2. Intermittent Test

Using scan tester, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

1. Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Code P0118 Flow Chart (3.4L) Coolant Temperature Sensor High Temperature Indicated. Scheme 71