GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Seville - RHD 🢒 DTC 🢒 DTC P0118

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor, or variable resistor, that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5  volts to the ECT signal circuit through a pull-up resistor. When the engine coolant temperature is cold, the sensor resistance is high. When the engine coolant temperature increases, the sensor resistance lowers. With high sensor resistance, the PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively high ECT signal voltage (a low temperature indication), this diagnostic trouble code (DTC) will set.

Conditions for Running the DTC
    • DTC P0112, P0113, P1111, or P1112 are not set.
    • The engine has been running for 60 seconds.
    • The intake air temperature (IAT) is more than -7°C (19°F).

Conditions for Setting the DTC
    • The ECT sensor temperature is less than -38°C (-36°F) for more than 10 seconds.
    • The conditions exists for less than 1 second.

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

Conditions for Clearing the MIL/DTC
    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

For intermittent conditions, refer to Intermittent Conditions .

Step

Action

Values

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. Connect the scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the ECT sensor display.

Does the scan tool indicate ECT below the specified value?

-24°C (-11°F)

Go to Step 4

Go to Step 3

3
  1. Review and record the scan tool Failure Records data.
  2. Operate the vehicle within the Failure Records conditions.
  3. With the scan tool, monitor the Specific DTC information for DTC P0118 until the test runs.

Does the scan tool indicate that DTC P0118 failed last test?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the ECT sensor connector. Refer to Engine Coolant Temperature Sensor Replacement .
  3. Turn the ignition to the RUN position with the engine OFF.
  4. Using DMM, measure the voltage between the ECT sensor signal and battery ground.

Does the DMM indicate a voltage near the specified value?

5V

Go to Step 5

Go to Step 10

5

  1. Install the scan tool.
  2. Connect a 3-amp jumper wire between the ECT signal and sensor ground circuits.
  3. Observe both of the 5-volt reference displays on the scan tool.

Do both 5 volt reference displays indicate OK?

--

Go to Step 7

Go to Step 6

6

Locate and repair the short between the ECT signal circuit and 5-volt reference A, or 5-volt reference B.

Is the action complete?

--

Go to Step 15

--

7
  1. Leave the jumper connected between the ECT signal and sensor ground circuits in the harness connector.
  2. Observe the ECT sensor display on the scan tool.

Does the scan tool indicate an ECT sensor display near the specified value?

150°C (302°F)

Go to Step 8

Go to Step 9

8

Important: If a short to a separate voltage source occurs, this DTC may set. The short may damage the ECT sensor. If this condition exists, a continuity test to all other PCM circuits will be necessary to diagnose the specific fault.

  1. Test for poor connections at the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  2. If the condition is found, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

9
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector. Refer to Powertrain Control Module Replacement .
  3. Test the ECT sensor ground for an open or poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  4. If the condition is found, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

10

Does the DMM indicate a voltage more than the specified value?

5 V

Go to Step 11

Go to Step 12

11

  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Test the ECT sensor signal circuit for a short to voltage.
  4. If the condition is found, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

12
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector.
  3. Test the ECT sensor signal circuit for an open or poor connections at the PCM. Refer to Repairing Connector Terminals in Wiring Systems.
  4. If the condition is found, repair as necessary. Refer to Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

13

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

Is the action complete?

--

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 15

--

15
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30  seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 16

Go to Step 2

16

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to the Diagnostic Trouble Code (DTC) List

System OK