For 1990-2009 cars
Engine Controls Components
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The powertrain control module (PCM) applies a voltage, about 5.0 volts, through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor resistance is high, therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts.

### Conditions for Running the DTC

The engine is running for 15 seconds.

### Conditions for Setting the DTC

• | The ECT sensor signal indicates an engine coolant temperature less than -39°C (-37°F).

• | The above condition is present for longer than 25 seconds.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.

• | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

Inspect for an intermittent condition.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

### Test Description

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

1. This step verifies that the fault is present.

2. If DTC P0118 can be repeated only by duplicating the Fail Records conditions, refer to Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the ECT sensor, refer to ECT Sensor Replacement. If the ECT sensor appears to be OK, the fault is intermittent, refer to Diagnostic Aids.

3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement/Programming.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, observe the ECT parameter.

Does the scan tool indicate the ECT parameter is less than the specified value?

-38°C (-36°F)

Go to Step 4

Go to Step 3

3 |

1. With a scan tool, review and record Fail Records data.
2. Operate the vehicle within Fail Records conditions as noted.

Does the scan tool indicate DTC P0118 failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 | Test the signal circuit of the ECT sensor for a short to voltage. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Connect a 3 amp fused jumper between the signal circuit of the ECT sensor and the ground circuit of the ECT sensor.
3. With a scan tool, observe the ECT parameter.

Does the scan tool indicate the ECT parameter is more than the specified value?

139°C (282°F)

Go to Step 7

Go to Step 6

6 |

1. Remove 3 amp fused jumper and connect it between the signal circuit at the ECT sensor and a good ground.
2. With a scan tool, observe the ECT parameter.

Does the scan tool indicate the ECT parameter is more than the specified value?

139°C (282°F)

Go to Step 8

Go to Step 9

7 | Inspect for faulty connections at the ECT Sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11
8 | Test the ground circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
9 | Test the signal circuit of the ECT sensor for an open. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
10 | Inspect for a faulty ground or signal circuit connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
11 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | Go to Step 13 | --
13 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Fail Record conditions as noted.

Does the DTC reset?

--

Go to Step 2

System OK