GM Service Manual Online
For 1990-2009 cars only

Object Number: 280854  Size: MF
Engine Controls Components
Cell 21: Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. A thermistor is a resistor whose value varies with temperature. The ECT sensor's resistance is high if the coolant temperature is cold, and the ECT sensor's resistance is low if the coolant temperature is warm. The ECT sensor is wired in series with a fixed resistor in the powertrain control module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts the voltage into a temperature reading. The PCM will receive a high voltage input if the coolant temperature is cold. The PCM will receive a low voltage input if the coolant temperature is warm. A DTC P0116 may set if the ECT sensor voltage does not indicate that the engine coolant temperature has increased during engine operation.

Conditions for Running the DTC

    • The engine has been running for at least 20 minutes.
    • The vehicle has been driven at speeds of 50 km/h (30 mph) or more at least once since an engine start.

Conditions for Setting the DTC

The engine coolant temperature variation that is indicated by the ECT sensor is less than the expected value.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.
    • The PCM records the operating conditions at the time that the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the DTC

    • The MIL turns OFF after 3 consecutive trips during which the diagnostic runs and does not detect a fault.
    • A History DTC clears after 40 consecutive warm-up cycles without a fault.
    • Use the scan tool Clear DTC Information function.

Diagnostic Aids

Check for the following conditions:

    • If a DTC P0106 and a DTC P0121 are also set, the malfunction may be in the sensor ground circuit.
    • Check for the correct operation of the engine's cooling system, including the correct coolant level. Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling.
    • A faulty thermostat can cause DTC P0116 to set in cold weather when the vehicle is started and allowed to sit while warming. Replace any thermostat suspected to be faulty. Refer to Thermostat Diagnosis in Engine Cooling.
    • Use the Temperature vs Resistance table in order to evaluate the possibility of a shifted ECT sensor. A shifted sensor could result in a DTC P0116. Refer to Temperature Versus Resistance .
    • Check for a faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in the ECT sensor electrical circuit. Inspect the wiring harness and the components for any of the following conditions:

    • Backed out terminals.
    • Incorrect mating of terminals.
    • Broken electrical connector locks.
    • Incorrectly formed terminals or damaged terminals
    • Faulty terminal-to-wire connections.
    • Physical damage to the wiring harness.
    • A broken wire inside the insulation.
    • Corrosion of electrical connections, of splices, or of terminals.

Repair any electrical circuit faults that were found. Refer to Wiring Repairs .

If you cannot duplicate DTC P0116, the information in the Freeze Frame data may help determine the conditions when the DTC set.

Test Description

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

  1. The OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

  2. This step checks for a faulty ECT sensor or ECT sensor circuit.

  3. This step checks the integrity of the ECT sensor input circuit.

  4. This step checks the integrity of the ECT sensor ground circuit.

  5. This step checks the integrity of the ECT sensor input circuit.

  6. A cooling system that prevents the engine from warming up properly and reaching the correct engine operating temperature within a specified time can cause a DTC P0116 to set. A thermostat that stays open slightly can cause a DTC P0116 to set.

  7. This step determines if DTC P0116 is the result of a hard failure or an intermittent condition.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Check for a DTC P0117 or DTC P0118 with a scan tool.

Is a DTC P0117 or DTC P0118 present?

--

Go to DTC P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage or DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

Go to Step 3

3

  1. Measure the actual coolant temperature.
  2. Turn ON the ignition, leaving the engine OFF.
  3. Observe the ECT sensor parameter on the scan tool.

Is the ECT sensor value displayed near the actual coolant temperature?

--

Go to Step 11

Go to Step 4

4

  1. Disconnect the ECT sensor electrical connector.
  2. Observe the ECT sensor parameter on the scan tool.

Does the scan tool indicate the specified value?

-40 C (-40°F)

Go to Step 5

Go to Step 8

5

  1. Jump the ECT sensor input circuit and the ground circuit together at the ECT sensor harness connector.
  2. Observe the ECT sensor parameter on the scan tool.

Does the scan tool indicate the specified value?

119°C (246°F)

Go to Step 13

Go to Step 6

6

  1. Jump the ECT sensor input circuit to chassis ground.
  2. Observe the ECT sensor parameter on the scan tool.

Does the scan tool indicate the specified value?

119°C (246°F)

Go to Step 7

Go to Step 8

7

Repair the open or electrical resistance in the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 14

Go to Step 9

8

  1. Turn OFF the ignition.
  2. Disconnect the PCM electrical connector C2.
  3. Check the ECT sensor input circuit for a short or high electrical resistance.
  4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 9

9

  1. Check for a faulty connection at the PCM and the ECT electrical connectors.
  2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 14

Go to Step 10

10

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 14

--

11

  1. Inspect the engine cooling system for any of the following conditions:
  2. • Faulty thermostat -- Refer to Thermostat Diagnosis in Engine Cooling.
    • Low coolant level
    • Incorrect coolant
    • Faulty cooling system operation -- Refer to Engine Fails To Reach Normal Operating Temperature in Engine Cooling.
  3. Repair as necessary.

Was a repair necessary?

--

Go to Step 14

Go to Step 12

12

  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode, using the scan tool.
  3. Operate the vehicle within the Freeze Frame conditions as specified.

Does a DTC P0116 set?

--

Go to Step 13

Go to Diagnostic Aids

13

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

Is the action complete?

--

Go to Step 14

--

14

  1. Perform the scan tool Clear DTC Information function and road the vehicle wihin the Freeze Frame conditions that set the DTC.
  2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on scan tool?

--

Go to the applicable DTC table

System OK