DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage


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Circuit Description

The Engine Coolant Temperature (ECT) sensor contains a semiconductor device which changes the resistance based on the temperature (a thermistor). The ECT sensor is mounted in the left bank cylinder head near the front of the engine. The ECT sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine the coolant temperature.

When the coolant is cold, the sensor (thermistor) resistance is high. The PCMs signal voltage is only pulled down a small amount through the sensor to a ground; therefore, the PCM senses a high signal voltage (low temperature). When the coolant is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount; therefore, the PCM senses a low signal voltage (high temperature). At normal operating temperature, the voltage should measure about 1.5-2.0 volts at the PCM.

When the PCM senses a signal voltage higher than the normal operating range of the sensor, this DTC sets.

Conditions for Running the DTC

The engine run time is greater 60 seconds.

Conditions for Setting the DTC

Action Taken When the DTC Sets

Conditions for Clearing the MIL/DTC

Diagnostic Aids

Important

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step determines if the malfunction is present. For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A . Using this kit prevents damage to the harness connector terminals.
  1. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed.
  1. An engine coolant temperature above 139C (282F) indicates the PCM and ECT sensor wiring is OK.
  1. An engine coolant temperature above 139C (282F) indicates the PCM and ECT sensor signal circuit is OK.
  1. Disconnecting the PCM allows using the DMM J 39200 in order to test continuity of the circuits. This aids in locating an open or a shorted circuit.
  1. Disconnecting the PCM allows using the DMM J 39200 in order to test continuity of the circuits. This aids in locating an open or a shorted circuit.
  1. Inspect for proper terminal tension/connections at the PCM harness before replacing the PCM.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install a scan tool.
  2. Turn ON the ignition leaving the engine OFF.
  3. Monitor the ECT sensor display on the Engine 1 Data List of the scan tool.

Is the ECT sensor at the specified value?

-39C (-38F)

Go to Step 4

Go to Step 3

3

  1. Turn ON the ignition leaving the engine OFF.
  2. Review the Freeze Frame and/or Failure Records data for this DTC and observe the parameters.
  3. Turn OFF the ignition for 15 seconds.
  4. Start the engine.
  5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
  6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Disconnect the ECT sensor electrical connector.
  2. Jumper the ECT sensor harness terminals together.
  3. Observe the engine coolant temperature parameter on the scan tool.

Is the ECT sensor at the specified value?

140C (284F)

Go to Step 9

Go to Step 5

5

Jumper the ECT sensor signal circuit to a known good ground. Is the ECT sensor at the specified value?

140C (284F)

Go to Step 8

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the same side as the manufacturer's logo. Refer to PCM Replacement/Programming .
  3. Test the ECT sensor signal circuit for an open.

Is the ECT sensor signal circuit open?

--

Go to Step 7

Go to Step 11

7

Repair the ECT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete?

--

Go to Step 14

--

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector C2 located on the same side as the manufacturer's logo. Refer to PCM Replacement/Programming .
  3. Test the ECT sensor ground circuit for an open.

Is the ECT sensor ground circuit open?

--

Go to Step 10

Go to Step 11

9

Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . Is the action complete?

--

Go to Step 14

--

10

Repair the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete?

--

Go to Step 14

--

11

  1. Test for a short to voltage on the signal circuit.
  2. If you find the signal circuit shorted to a voltage repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 12

12

  1. Inspect for faulty connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
  2. If you find a poor connection repair the condition as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

13

Important:

Program the replacement PCM. Refer to PCM Replacement/Programming .

Replace the PCM. Is the action complete?

--

Go to Step 14

--

14

  1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
  2. Idle the engine at the normal operating temperature.
  3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 15

Go to Step 2

15

Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the applicable DTC table

System OK