GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2006 🢒 VUE - FWD 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 DTC P0118
Table 1: DTC P0118

Circuit Description

This diagnostic monitors the signal circuit of the engine coolant temperature (ECT) sensor. The ECT sensor is a variable resistor that measures the temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit. If the PCM detects a high ECT signal voltage, which is a low temperature indication, this DTC sets.

The following table illustrates the difference between temperature, resistance, and voltage:

ECT

ECT Resistance

ECT Signal Voltage

Cold

High

High

Warm

Low

Low

DTC Descriptor

This diagnostic procedure supports the following DTC:

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

Conditions for Running the DTC
    • The ignition is ON.
    • DTC P0117, is not set.
    • DTC P0118 runs continuously once the above conditions are met.

Conditions for Setting the DTC
    • The PCM detects that the ECT sensor signal voltage is 4.92 volts or more.
    • The above condition is present for at least 2 seconds.

Action Taken When the DTC Sets
    • The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame/Failure Records.
    • The PCM enters the Fail Safe Function in which the coolant temperature will use default values and the fuel control system will operate in OPEN LOOP.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids
    • If a short to a separate 5-volt source occurs this DTC may set, if this is found to be the condition a continuity test to all other PCM circuits will be necessary to diagnose the specific circuit.
    • Use the Temperature vs Resistance table in order to test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in a driveability condition. If the engine has sat overnight, the engine coolant temperature and the intake air temperature values should display within a few degrees. If the temperatures are not within 3°C (5°F), refer to Temperature Versus Resistance - Intake Air Temperature Sensor .
    • After starting the engine, the ECT should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

    2.

  2. This step tests the signal circuit of the ECT sensor for a short to another 5.0 volt reference circuit.

    3.

  3. After replacing the PCM a new minimum throttle position and idle speed must also be established.

DTC P0118

Step

-

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the engine coolant temperature (ECT) sensor parameter with a scan tool.

Does the scan tool indicate that the ECT is at the specified value?

-40°C (-40°F)

Go to Step 4

Go to Step 3

3
  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data.

Does the DTC fail this ignition cycle?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .
  3. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and the low reference circuit of the ECT sensor.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the ECT parameter with a scan tool.

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

168°C (334°F)

Go to Step 9

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a good ground.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the ECT parameter with a scan tool.

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

168°C (334°F)

Go to Step 8

Go to Step 6

6

Did the fuse in the jumper wire open?

--

Go to Step 11

Go to Step 7

7

Test the signal circuit of the ECT sensor for an open circuit or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

8

Test the low reference circuit of the ECT sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

9

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the signal circuit of the ECT sensor and a good ground.
  3. Start the engine.

Do any additional DTCs set?

--

Go to Step 13

Go to Step 10

10

Test for an intermittent and for a poor connection 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 16

Go to Step 14

11

Important: A short to voltage in signal circuit of the ECT sensor will cause ECT sensor failure. Replace the ECT sensor after you repair the short to voltage.

Test the signal circuit of the ECT sensor for short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

12

Test for an intermittent and for a poor connection at the powertrain control module (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 16

Go to Step 15

13

Repair the short between the signal circuit of the ECT sensor and the circuit for which the DTC set. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 16

--

14

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

Did you complete the replacement?

--

Go to Step 16

--

15

  1. Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.
  2. Perform the idle learn procedure. Refer to Idle Learn .

Did you complete the replacement?

--

Go to Step 16

--

16
  1. Use the scan tool in order to clear the DTCs.
  2. Turn the ignition OFF for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC.

Does the DTC run and pass?

--

Go to Step 17

Go to Step 2

17

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK