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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Riviera 🢒 DTC 🢒 DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

Object Number: 197640 Size: SF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Engine Coolant Temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The PCM applies a voltage (about 5.0 volts) through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor (thermistor) resistance is high, therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts. DTC P0118 will set when the PCM detects an excessively high signal voltage on the engine coolant temperature sensor signal circuit.

Conditions for Running the DTC

Engine run time longer than 15 seconds

Conditions for Setting the DTC
    • The ECT sensor signal indicates an engine coolant temperature less than -39°C (-39°F).
    • Above condition present for at least 10 seconds.

Action Taken When the DTC Sets
    • The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

Conditions for Clearing the MIL/DTC
    • The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using a scan tool.

Diagnostic Aids

Check for the following conditions:

    • Poor connection at PCM.
        Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness.
        Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the malfunction.
    • Skewed or mis-scaled ECT Sensor.
        Refer to Temperature Versus Resistance table.

If DTC P0118 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was last set. If it is determined that the DTC occurs intermittently, performing the DTC P1115 Diagnostic Chart may isolate the cause of the malfunction.

Test Description

Number(s) below refer to the Step number(s) on the Diagnostic Table.

  1. Verifies that the malfunction is present.

    2.

  2. If DTC P0118 can be repeated only by duplicating the Fail Records conditions. The Temperature vs Resistance 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; go to Diagnostic Aids.

    3.

  3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

DTC P0118 - ECT Sensor Circuit High Voltage

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn ON the ignition.
  2. Observe ECT displayed on the scan tool.

Is ECT less than the specified value?

-38°C (-36°F)

Go to Step 4

Go to Step 3

3

  1. Verify that the ignition is ON.
  2. Review and record scan tool Fail Records data.
  3. Operate the vehicle within Fail Records conditions as noted.
  4. Monitor Specific DTC info for DTC P0118, using a scan tool.

Does the scan tool indicate DTC P0118 failed?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the PCM and the ECT harness connectors.
  3. Turn ON the ignition.
  4. Check the ECT sensor signal circuit for a short to voltage.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 13

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Reconnect the PCM.
  3. Jumper the ECT signal circuit and the sensor ground circuit together at the ECT sensor harness connector.
  4. Turn ON the ignition.
  5. Observe ECT displayed on the scan tool.

Is ECT at the specified value?

140°C (284°F)

Go to Step 7

Go to Step 6

6
  1. Jumper the ECT signal circuit at the ECT sensor harness connector to chassis ground.
  2. Observe ECT displayed on the scan tool.

Is ECT at the specified value?

140°C (284°F)

Go to Step 8

Go to Step 9

7
  1. Check for poor connections at the ECT sensor.
  2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Step 13

Go to Step 11

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Check the ECT sensor ground circuit for an open or a short to voltage between the PCM and the ECT sensor.
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 13

Go to Step 10

9
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Check the ECT signal circuit for an open.
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 13

Go to Step 10

10
  1. Check for a poor sensor ground or ECT signal circuit terminal connection at the PCM.
  2. Check for a ECT signal circuit terminal connection at the PCM.
  3. Check for a ECT signal circuit terminal connection at the PCM.
  4. If a problem is found, replace terminal(s) as necessary. Refer to Repairing Connector Terminals .

Was a problem found?

--

Go to Step 13

Go to Step 12

11

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

Is the action complete?

--

Go to Step 13

--

12

Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 13

--

13
  1. Review and record scan tool Fail Records data.
  2. Clear the DTCs.
  3. Operate the vehicle within Fail Records conditions as noted.
  4. Monitor Specific DTC info for DTC P0118, using a scan tool.

Does the scan tool indicate DTC P0118 failed?

--

Go to Step 2

System OK