GM Service Manual Online
For 1990-2009 cars only

Object Number: 394105  Size: SF
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Pickup Engine Sensors
OBD II Symbol Description Notice

Circuit Description

The engine coolant temperature (ECT) sensor is a thermistor. The control module supplies the ECT sensor with a reference voltage on the ECT signal circuit and a ground circuit. When the ECT sensor resistance is high, indicating a cold sensor, the ECT sensor signal voltage remains near the supplied voltage. The ECT sensor decreases the signal voltage as the ECT sensor resistance is low, indicating a warm sensor. The control module monitors the ECT sensor signal circuit voltage in order to calculate the engine temperature.

this DTC is designed to detect intermittent low voltage signals on the ECT sensor signal circuit.

Conditions for Running the DTC

The engine has been running for more than 5 seconds.

Conditions for Setting the DTC

The ECT voltage is less than 0.25 volt for 1 second or less.

Action Taken When the DTC Sets

    • The control module stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL).
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
    • A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
    • Use the scan tool Clear Information function.

Diagnostic Aids

An intermittent short to ground in the ECT sensor signal circuit could result in a DTC P1114. If the low ECT voltage reading is present, additional sensor circuit voltage codes could be set. Refer to any non-intermittent DTCs that are set.

The scan tool displays the engine temperature in degrees centigrade. After the engine is started, the temperature should rise steadily to about 90°C (194°F) then stabilize when the thermostat opens.

Use the Temperature vs. Resistance Value scale in order to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed or mis-scaled sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs Resistance .

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The number below refers to the step number on the diagnostic table.

  1. If the ECT sensor voltage is less than 0.25 volts, then the condition is present. Even though DTC P0117 did not set, this DTC is more comprehensive and may aid in diagnosis.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used.

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

  1. Install the scan tool.
  2. Turn ON the ignition leaving the engine OFF.
  3. Display the ECT sensor voltage.

Is the ECT sensor voltage less than the specified value?

0.25 V

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

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the ECT sensor harness connector.
  3. Inspect the ECT sensor harness connector and terminals.

Did you find a problem?

--

Go to Step 6

Go to Step 4

4

  1. Disconnect the VCM C2 and C3 connectors.
  2. Inspect the terminals and connectors.

Did you find a problem?

--

Go to Step 6

Go to Step 5

5

  1. Reconnect the VCM and ECT sensor harness connectors.
  2. Turn ON the ignition leaving the engine OFF.
  3. Check for an intermittent short to ground in the ECT sensor signal circuit while moving the harness in various locations.
  4. Display the ECT sensor voltage while moving the harness.

Did the voltage fluctuate?

--

Go to Step 6

Go to Diagnostic Aids

6

Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 7

--

7

  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle, with the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 8

Go to Step 2

8

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK