GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit. If the ECM detects an intermittent low ECT signal voltage, which is a high temperature indication, this DTC sets.

The following table illustrates the difference between temperature, resistance, and voltage:

ECT

ECT Resistance

ECT Signal Voltage

Cold

High

High

Warm

Low

Low

DTC Descriptor

This diagnostic supports the following DTC:

DTC P1114 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent Low Voltage

Conditions for Running the DTC

    • The engine run time is more than 120 seconds.
    • This DTC runs continuously when the above condition is met.

Conditions for Setting the DTC

The ECM detects that the engine coolant temperature is more than 149°C (300°F) intermittently.

Action Taken When the DTC Sets

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC

    • 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 non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

    • Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition.
    • If the vehicle has set overnight, the ECT sensor and the intake air temperature (IAT) sensor values should display within 3°C (5°F). Refer to Temperature Versus Resistance .
    • For an intermittent condition, refer to Intermittent Conditions .

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Observe the DTC information with a scan tool.

Is DTC P0117 set?

Go to DTC P0117

Go to Step 3

3

Observe the Engine Coolant Temperature (ECT) sensor parameter with a scan tool while moving the ECT sensor connector and the engine control module (ECM) connector. Refer to Inducing Intermittent Fault Conditions in Wiring Systems.

Does the scan tool indicate an abrupt change in value?

Go to Step 5

Go to Step 4

4

Observe the ECT sensor parameter with a scan tool while moving the wiring harness between the ECT sensor and the ECM. Refer to Inducing Intermittent Fault Conditions in Wiring Systems.

Does the scan tool indicate an abrupt change in value?

Go to Step 6

Go to Diagnostic Aids

5

Repair the connector/terminal as necessary. Refer to Connector Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 7

--

6

Repair the harness/wiring as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 7

--

7

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 8

8

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK