For 1990-2009 cars

### Circuit Description

The DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage diagnostic monitors the ECT sensor signal. The ECT sensor is a thermistor. A thermistor is a resistor whose value varies with the temperature. The electrical resistance of the ECT sensor is high when the coolant temperature is cold, and the resistance is low when the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The voltage measured by the PCM will be high when the coolant temperature is cold, and low when the coolant temperature is warm.

Temperature | ECT Resistance | ECT Signal Voltage
--- | --- | ---
Cold | High | High
Warm | Low | Low

### Condition for Running the DTC

The ignition is ON or the engine is running.

### Conditions for Setting the DTC

• | The ECT sensor signal indicates an engine coolant temperature of -40°C (-40°F).

• | The above condition is met for at least 5 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL).

• | The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

• | The PCM enters the Fail-Safe Function and assumes the engine coolant temperature is 30°C (86°F) on M/T and 3 speed A/T, 31°C (88°F) on 4 speed A/T.

### Conditions for Clearing the MIL/DTC

• | The MIL turns off after 3 consecutively passing cycles without a fault present.

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

• | Perform the scan tool clear DTC Information function in order to clear the DTC.

### Diagnostic Aids

Check for any of the following conditions:

• | A damaged wiring harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving the connectors and the wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the fault.

• | When replacing the ECT sensor, the Temperature to Resistance Value scale may be used to test the sensor at various temperature levels to evaluate the possibility of a shifted and incorrectly calibrated sensor. A shifted sensor may result in poor driveability complaints. Refer to Temperature Versus Resistance .

• | After the engine is started, the ECT sensor should rise steadily to about 95°C (203°F) and stabilize when the thermostat opens. Verify that the engine is not overheating and has not been subjected to conditions which may create an overheating conditions (i.e., overload, trailer towing, hilly terrain, heavy stop-and-go traffic, etc.).

• | A shorted to voltage sensor signal circuit may cause DTC P0118 to set.

If a DTC P0118 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool clear DTC information function. Road test the vehicle while monitoring the DTC P0118 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0118 appears in the Not Ran Since Code Cleared list, the P0118 diagnostic has not yet run. When the DTC P0118 does not appear in the Not Ran Since Code Cleared list, the P0118 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P0118 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

An intermittent malfunction may be caused by a fault in the ETC sensor circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If the DTC P0118 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

### Test Description

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

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Determine if a fault is present.

3. Review the Freeze Frame data to determine when the DTC set. Always record this information.

4. This step determines if the fault is caused by an open or shorted signal return circuit, an open in the ground circuit, or by a malfunctioning ECT sensor.

5. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0118 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0118 appears in the Not Ran Since Code Cleared list, the DTC P0118 diagnostic has not yet run. When the DTC P0118 does not appear in the Not Ran Since Code Cleared list, the DTC P0118 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0118 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Turn ON the ignition, leaving the engine OFF.
2. Install a scan tool.
3. Observe the engine coolant temperature (ECT) parameter on the scan tool.

Is the ECT less than or equal to the specified value?

-40°C (-40°F)

Go to Step 4

Go to Step 3

3 |

1. Perform the scan tool Clear DTC Information function.
2. Operate the vehicle within the Freeze Frame conditions as noted.

Is DTC P0118 set?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Disconnect the ECT sensor electrical connector.
2. Jumper the ECT signal circuit and the sensor ground circuit together at the ECT sensor harness connector.
3. Observe the ECT parameter on the scan tool.

Does the ECT equal the specified value?

165°C (329°F)

Go to Step 6

Go to Step 5

5 |

1. Jumper the ECT signal circuit at the sensor harness connector to chassis ground.
2. Observe the ECT parameter on the scan tool.

Does the ECT equal the specified value?

165°C (329°F)

Go to Step 7

Go to Step 8

6 |

1. Inspect for a faulty electrical connection at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 10

7 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Check for an open in the ECT sensor ground circuit.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 9

8 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Check for an open in the ECT sensor signal circuit.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 9

9 |

1. Check for a faulty ECT sensor ground or signal circuit connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 11

10 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 12 | --
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 12 | --
12 |

1. Turn OFF the ignition.
2. Remove the DOME fuse for 30 seconds.
3. Install the DOME fuse.
4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTC P0118 diagnostic test has run.

Does the DTC run and pass?

--

Go to Step 13

Go to Step 2

13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK