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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2003 🢒 Chevrolet T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P0118

DTC P0118 Without RPO CTF

Circuit Description

The engine coolant temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively high ECT signal voltage, which is a low temperature indication, this DTC will set.

Conditions for Running the DTC

The engine has been running for more than 8 minutes.

Conditions for Setting the DTC

The ECT sensor temperature is less than -39°C (-38°F) for 20 seconds.

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.

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.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
    • If a short to a separate 5-volt source occurs, this DTC may set. If this is the problem, a continuity test to all other ECM circuits will be necessary in order to diagnose the specific circuit.
    • After starting the engine, the ECT should rise steadily to about 90°C (194°F), then stabilize when the thermostat opens.
    • Use the Temperature vs. Resistance table in order to test the ECT sensor at various temperature levels and in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in poor driveability conditions. Refer to Temperature Versus Resistance .
    • If the condition is suspected of being intermittent, refer to Intermittent Conditions .

Test Description

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

  1. If DTC P0118 can only be repeated by duplicating the Failure Records, refer to the 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. If the ECT sensor appears to be OK, the malfunction is intermittent. Refer to Diagnostic Aids.

    2.

  2. 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.

    3.

  3. The ECM in this vehicle use an electrically erasable programmable read-only memory (EEPROM). If the ECM is replaced, the new ECM must be programmed.

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. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to observe the ECT sensor temperature.

Is the ECT sensor temperature less than the specified value?

-38°C (-36°F)

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame/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 or as closely as possible to the Freeze Frame/Failure Records conditions.

Does the DTC reset?

--

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 between the signal circuit of the ECT sensor and the low reference circuit. Refer to Using Fused Jumper Wires in Wiring Systems.
  4. Turn ON the ignition, with the engine OFF.
  5. Use the scan tool in order to observe the ECT sensor temperature.

Is the ECT sensor temperature more than the specified value?

138°C (280°F)

Go to Step 8

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 ground.
  3. Turn ON the ignition, with the engine OFF.
  4. Use the scan tool in order to observe the ECT sensor temperature.

Is the ECT sensor temperature more than the specified value?

138°C (280°F)

Go to Step 7

Go to Step 6

6
  1. Test the signal circuit of the ECT sensor for the following conditions:
    2. • A short to voltage
    • A high resistance
    • An open circuit
  2. Repair the circuit as necessary. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

7
  1. Test the reference low circuit of the ECT sensor for a high resistance or an open.
  2. Repair the circuit as necessary. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8
  1. Test the signal circuit of the ECT sensor for the following conditions:
    2. • A short to voltage
    • Any poor connections at the harness connector of the ECT sensor.
  2. Repair the connections as necessary. Refer to Circuit Testing and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9
  1. Inspect for poor connections at the harness connector of the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .
  2. Repair the connections as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

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

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data .

Did you complete the replacement?

--

Go to Step 12

--

12
  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 13

Go to Step 2

13

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

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

--

Go to Diagnostic Trouble Code (DTC) List

System OK