GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 GMC C Sierra - 2WD (LPG) 🢒 DTC 🢒 DTC P0118

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. The ECT thermistor has high resistance when cold and low resistance when hot. The powertrain control module (PCM) supplies about 5 volts on the ECT signal circuit. The PCM also supplies a ground circuit to the ECT sensor. When the ECT resistance is high the ECT signal voltage remains near the supplied 5 volts. As the ECT sensor warms and resistance drops, more signal circuit voltage is pulled lower to the sensor ground. The PCM and the alternative fuels ECM monitor the ECT signal circuit voltage in order to determine the engines temperature.

This DTC sets when the ECT signal circuit voltage is above the normal operating range of the sensor.

Conditions for Running the DTC
    • The engine is operating on alternative fuel.
    • The engine has been operating for greater than 5 seconds when the intake air temperature (IAT) is greater than 0°C (32°F).
        or
        The engine has been operating for greater than 10 minutes when the IAT is less than 0°C (32°F).

Conditions for Setting the DTC

The Alternative Fuels ECM monitors an ECT sensor signal voltage of greater than 4.8 volts for at least 5 seconds continuously.

Action Taken When the DTC Sets

    • A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History.
    • The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails.
    • The Alternative Fuels ECM will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data.

Conditions for Clearing the MIL/DTC

    • The Last Test Failed status will clear when the DTC runs and passes.
    • The Alternative Fuels ECM will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes.
    • The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC.
    • All DTC Information can be cleared with a scan tool.

Test Description

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

  1. This step determines if the condition is present.

    2.

  2. This step determines if the condition affects the PCM.

    3.

  3. This step determines if the ECT sensor is the open condition.

    4.

  4. This step determines if the sensor ground circuit is the open condition.

    5.

  5. This step determines if the ECT signal circuit wiring is the open condition.

    6.

  6. If the connector terminals pass inspection test the sensor signal circuit for a short to a 5-volt reference circuit. Although an unlikely failure, this condition should be diagnosed before replacing the PCM.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls?

--

Go to Step  2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2

  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 also may operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure Records data.
  5. Observe the Diagnostic Trouble Code (DTC) Information from the following control modules with a scan tool:
    6. • Alternative Fuels ECM
    • PCM

Does the DTC fail this ignition cycle?

--

Go to Step 3

Go to Intermittent Conditions

3

  1. With a scan tool, establish communication with the PCM.
  2. Observe the ECT Sensor data parameter.

Does the ECT sensor data parameter indicate ECT temperature colder than the specified value?

-34°C (-27°F)

Go to Step 4

Go to Step 7

4

  1. Disconnect the ECT sensor.
  2. Connect a 3-amp fused jumper between the ECT sensor connector terminals.

    3. If the fuse of the jumper opens, repair the short to voltage on the ECT sensor signal circuit. If a short to voltage condition is observed, inspect the sensor for an open condition after the wiring repair is completed.

Does the ECT sensor data parameter indicate ECT temperature warmer than the specified value?

140°C (284°F)

Go to Step 8

Go to Step 5

5

Connect the fused jumper between the ECT signal circuit and a known good ground.

Does the ECT sensor data parameter indicate ECT temperature warmer than the specified value?

140°C (284°F)

Go to Step 11

Go to Step 6

6

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector C1. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Test the ECT signal circuit for continuity with a DMM.

Does the DMM display continuity?

--

Go to Step 9

Go to Step 12

7
  1. Turn the ignition OFF.
  2. Disconnect the Alternative Fuels ECM connector C002. Refer to Alternative Fuels Engine Control Module Replacement .
  3. Test the ECT signal circuit for continuity with a DMM.

Does the DMM display continuity?

--

Go to Step 10

Go to Step 13

8

Inspect for proper terminal contact at the harness connector of the ECT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 14

9

Inspect for proper terminal contact at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 15

10

Inspect for proper terminal contact at the harness connector of the Alternative Fuels ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 17

Go to Step 16

11

Repair the open sensor ground circuit between the ECT sensor connector and the PCM. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

--

Go to Step 17

--

12

Repair the open ECT signal circuit between the ECT sensor connector and the PCM. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

--

Go to Step 17

--

13

Repair the open ECT signal circuit between the ECT signal circuit splice and the Alternative Fuels ECM. Refer to Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you complete the repair?

--

Go to Step 17

--

14

Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 17

--

15

Important: KL6 models require a switchover to gasoline with a scan tool in order to perform the Crankshaft Position Variation Learn Procedure.

KL8 models do not require the Crankshaft Position Variation Learn Procedure.

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.

Did you complete the replacement?

--

Go to Step 17

--

16

Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 17

--

17
  1. Use the scan tool in order to clear the DTCs from the following control modules:
    2. • Alternative Fuels ECM
    • PCM
  2. Turn OFF the ignition for 30 seconds.
  3. 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 18

Go to Step 2

18

With a scan tool, select Capture Info in order to observe the stored information.

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

--

Go to Diagnostic Trouble Code (DTC) List

System OK