P0118

Diagnostic Chart:

Wiring Chart:

CIRCUIT DESCRIPTION

The Engine Coolant Temperature (ECT) sensor is a thermistor that controls the signal voltage to the PCM. When the engine is cold, the sensor resistance is high, therefore the PCM will see a high signal voltage. As the engine warms, the sensor resistance becomes less and the voltage drops. The voltage measured across the thermister is interpreted as a temperature.

CONDITIONS FOR SETTING THE DTC

^ The engine has been running for at least 8 minutes.

^ The ECT is less than -30°C (-22°F).

^ The conditions were met for 2 seconds.

ACTION TAKEN WHEN THE DTC SETS

^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive drive trip the diagnostic runs and tails.

^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic tails, the Failure Records store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC

^ The PCM will turn the MIL off after three consecutive trips without a fault condition.

^ A History DTC will clear after forty consecutive warm-up cycles during which the diagnostic does not fail (the coolant temperature has risen 5°C (40°F) from start up coolant temperature and engine coolant temperature exceeds 71°C (160°F) that same ignition cycle).

^ Use of a Scan Tool will clear the DTC codes.

DIAGNOSTIC AIDS

Check the harness routing for a potential short to voltage. After the engine is started, the ECT temperature should rise steady to about 85°C (185°F). A mis-scaled sensor could result in poor driveability complaints.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. This step determines if P0118 is a hard failure or an intermittent condition.

3. This step will determine if there is a wiring problem or a malfunctioning PCM.

9. This step determines if there is a short to voltage on the signal circuit. A short to voltage increases current flow through the sensor which overwhelms the sensor. This doesn't allow the sensor to pull-down the circuit to the correct voltage and thus displaying the correct temperature.

10. After repairing the short to voltage, check the sensor for proper operation.