P0118 Engine Coolant Temperature sensor circuit high

P0118 code - the Powertain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return). When the engine is cold, the PCM will operate in open loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached. The PCM uses inputs form the ECT sensor for the following calculations: For engine coolant temperature gauge operation through CCD or PCI (J1850) communications, injector pulse-widht, ASD relay shut down times, sprak-advance curves, idle Air Control (IAC) motor key-on steps, pulse-widht prime-short during cranking, O2 sensor closed loop times, purge solenoid on/off times, EGR solenoid on/off times (if equipped), leak detection pump operation (if equipped), radiator fan relay on/off times (if equipped).

When monitored this code with the ignition off, battery voltage greater than 10.4 volts. Set conditions, the Engine Coolant Temperature sensor input voltage is above the maximum acceptable threshold. Default actions the ETC light will illuminate, MIL light will illuminate. When this DTC is active the engine speed, torque and vehicle speed are limited to a limp in mode.

Possible causes P0118 code:

• ECT signal circuit shorted to voltage.
• ECT signal circuit open/high resistance.
• Sensor ground circuit open/high resistance.
• Engine Coolant Temperature (ECT) sensor.
• Powertrain Control Module (PCM).

Diagnose code P0118 Engine Coolant Temperature sensor circuit high

Step 1. Check for an active DTC

Diagnose and repair any system voltage DTC before continuing with this test. Turn the ignition on, with the scan tool, read DTC.

Is the DTC active or pending?

Yes, go to step 2.

No, perform the PCM intermittent condition.

Step 2. Check the ECT signal circuit for a short to voltage

Turn the ignition off, disconnect the ECT sensor harness connector. Turn the ignition on, measure the voltage between ground and the ECT signal circuit in the ECT sensor harness connector.

Is the voltage above 5.2 volts?

Yes, repair the ECT signal circuit for a short to voltage.

No, go to step 3.

Step 3. Check the ECT signal circuit for an open/high resistance

Turn the ignition off, disconnect the PCM harness connector. Measure the resistance of the ECT signal circuit between ECT sensor harness connector to the PCM harness connector.

Is the resistance below 3.0 Ohms?

Yes, go to step 4.

No, repair the ECT signal circuit for an open or high resistance.

Step 4. Check the sensor ground circuit for an open/high resistance

Measure the resistance of the sensor ground circuit between the ECT sensor harness connector to the PCM harness connector.

is the resistance below 3.0 Ohms?

Yes, go to step 5.

No, repair the sensor ground circuit for an open or high resistance.

Step 5. ECT sensor

Reconnect the PCM harness connector. Connect a jumper between the ECT signal circuit and the sensor ground circuit in the ECT harness connector. Turn the ignition on, with the scan tool, read DTC.

Does the scan tool display as described above?

Yes, verify that there is good pin to terminal contact in the ECT sensor and Powertrain Control Module connectors. If OK, replace the Engine Coolant Temperature (ECT) sensor.

No, go to step 6.

     Note : Remove the jumper before continuing.

Step 6. Check related PCM and component connections

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