GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 DTC 🢒 DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

Object Number: 293715 Size: SF
A/C Refrigerant Pressure Sensor, TP Sensor, Map Sensor, ECT Sensor, IAT sensor
Engine Controls Components
OBD II Symbol Description Notice
ESD Notice
ESD Notice

Circuit Description

The engine coolant temperature (ECT) sensor contains a semiconductor--a device that changes resistance based on temperature. The ECT sensor has a signal circuit and a ground circuit. The PCM applies voltage of about 5.0 volts to the sensor on the signal circuit. The powertrain control module (PCM) monitors any voltage changes caused by changes in the resistance of the sensor, and uses this information to determine the engine coolant temperature.

When the engine coolant is cold, the sensor resistance is high, and the PCM signal voltage is only pulled down a slightly through the sensor to ground. The PCM, therefore, senses a high signal voltage or a low coolant temperature. When the engine coolant is warm, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the PCM to sense a low signal voltage or a high temperature.

Conditions for Running the DTC

Engine run time longer than 3 seconds

Conditions for Setting the DTC
    • The ECT sensor signal indicates an engine coolant temperature less than -13°C (9°F).
    • Above condition present for at least 10 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
    • The PCM turns the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
    • A last test failed (current DTC) clears when the diagnostic runs and does not fail.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • Use a scan tool in order to clear the MIL/DTC.
    • Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description , Clearing Diagnostic Trouble Codes.

Diagnostic Aids

Check for a skewed or mis-scaled ECT Sensor. Refer to theTemperature vs Resistance table.

If DTC P0118 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set.

If the problem is intermittent, refer to Intermittent Conditions .

Test Description

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

  1. Verifies that the malfunction is present.

    2.

  2. If DTC P0118 can be repeated only by duplicating the Failure Records conditions, refer to the Temperature vs Resistance

  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.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

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

2

Observe ECT displayed on the scan tool.

Is ECT less than the specified value?

-31°C (-24°F)

Go to Step 4

Go to Step 3

3

  1. Turn the key to Off, wait 15 seconds, then turn the key to On.
  2. Review and record the Failure Records data.
  3. Operate the vehicle within Failure Records conditions as noted.
  4. Using a scan tool, monitor Specific DTC info for DTC P0118.

Does the scan tool indicate DTC P0118 failed?

--

Go to Step 4

Refer to Diagnostic Aids.

4
  1. Turn the key to Off.
  2. Disconnect the ECT sensor.
  3. Jumper the ECT signal circuit and the sensor ground circuit together at the ECT sensor harness connector
  4. Turn the key to On.
  5. Observe ECT displayed on the scan tool.

Is ECT greater than the specified value?

130°C (266°F)

Go to Step 7

Go to Step 5

5
  1. Turn the key to Off.
  2. Disconnect the PCM.
  3. Turn the key to On.
  4. Check the ECT sensor signal circuit for a short to voltage.
  5. If a problem is found, repair as necessary.

Was a problem found and corrected?

--

Go to Step 13

Go to Step 6

6
  1. Jumper the ECT signal circuit at the ECT sensor harness connector to chassis ground.
  2. Observe ECT displayed on the scan tool.

Is ECT greater than the specified value?

130°C (266°F)

Go to Step 8

Go to Step 9

7
  1. Check for poor connections at the ECT sensor.
  2. If a problem is found, replace terminal(s) as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found and corrected?

--

Go to Step 13

Go to Step 11

8
  1. Turn the key to Off.
  2. Disconnect the PCM.
  3. Check the ECT sensor ground circuit for an open.
  4. If a problem is found, repair as necessary.

Was a problem found and corrected?

--

Go to Step 13

Go to Step 10

9
  1. Turn the key to Off.
  2. Disconnect the PCM.
  3. Check the ECT signal circuit for an open.
  4. If a problem is found, repair as necessary.

Was a problem found and corrected?

--

Go to Step 13

Go to Step 10

10
  1. Check for a poor sensor ground or ECT signal circuit terminal connection at the PCM
  2. If a problem is found, replace terminal(s) as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found and corrected?

--

Go to Step 13

Go to Step 12

11

Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .

Is the action complete?

--

Go to Step 13

--

12

Replace the PCM.

Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming

Is the action complete?

--

Go to Step 13

--

13
  1. Clear DTCs with the scan tool.
  2. Turn the key to Off and wait 15 seconds
  3. Operate vehicle within the conditions that are required for this diagnostic to run. Refer to Conditions for Running the DTC.

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

--

Go to Step 14

Go to Step 2

14

Review Captured Info using the scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to the applicable DTC table

System OK