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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Corvette 🢒 Engine 🢒 Engine Cooling 🢒 DTC P0118

Circuit Description

The engine coolant temperature (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 a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. 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 low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

Conditions for Running the DTC

The engine has been running for more than 60 seconds.

Or

The engine run time is less than 60 seconds if the intake air temperature (IAT) is more than 0°C (32°F).

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.
    • 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

If a short to a separate 5-volt source occurs, this DTC may set. If this condition occurs, perform a continuity test to all other PCM circuits in order to diagnose the specific circuit.

After you start the engine, the engine coolant temperature (ECT) should rise steadily to approximately 90°C (194°F). The ECT should stabilize when the thermostat opens.

In order to evaluate the possibility of a skewed sensor, test the ECT sensor at various temperature levels. Refer to Temperature Versus Resistance .

If a malfunction is not present, refer to DTC P1115 .

If you suspect an intermittent condition, refer to Intermittent Conditions .

Step

Action

Value

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

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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 a scan tool in order to observe the ECT sensor temperature.

Does the scan tool indicate that the ECT sensor temperature is 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 for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. In order to operate the vehicle under similar conditions which set the DTC, use the following information:
    5. • The parameters listed in the Conditions for Running in the DTC
    • The data in the Freeze Frame/Failure Records

Does the DTC set?

--

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

Does the scan tool indicate 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 wire between the signal circuit of the ECT sensor and of a known good ground.
  3. Turn ON the ignition, with the engine OFF.
  4. With a scan tool, observe the ECT sensor temperature.

Does the scan tool indicate ECT sensor temperature greater 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 7

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

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

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

  1. Test the signal circuit of the ECT sensor for the following:
    2. • A short to voltage
    • A poor connection at the harness connector of the ECT sensor
  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 10

9
  1. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
  2. Inspect for poor connections at the harness connector of the PCM.
  3. Repair the connections 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 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 PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12
  1. Use a 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

Use a scan tool in order to observe the stored information in Capture Info.

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

--

Go to Diagnostic Trouble Code (DTC) List

System OK