GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptors

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

DTC P1115: Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

ECT Sensor Signal

P0117, P1114

P0118, P1115

P0118, P1115*

P0115

Low Reference

--

P0118, P1115

--

P0115

* Internal ECM damage may occur if the circuit is shorted to B+

Typical Scan Tool Data

ECT Sensor

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Engine operating in Closed Loop.

Parameter Normal Range: Varies with ambient temperature.

ECT Sensor Signal

129°C (264°F), 0.0 Volts

-40°C (-40°F), 5.0 Volts

-40°C (-40°F), 5.0 Volts*

Low Reference

--

-40°C (-40°F), 5.0 Volts

--

* Internal ECM damage may occur if the circuit is shorted to B+

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.

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

ECT

ECT Resistance

ECT Signal Voltage

Cold

High

High

Warm

Low

Low

Conditions for Running the DTC

    • The engine has been running for more than 2 minutes.
    • The DTCs run continuously when the above condition is met.

Conditions for Setting the DTC

P1114

The ECM detects that the ECT sensor is more than 149°C (300°F ) intermittently.

P1115

The ECM detects that the ECT sensor is less than -38°C (-34°F) intermittently.

Action Taken When the DTC Sets

DTCs P1114 and P1115 are Type C DTCs.

Conditions for Clearing the MIL/DTC

DTCs P1114 and P1115 are Type C DTCs.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views
    •  Engine Controls Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

    •  Scan Tool Data List
    •  Scan Tool Data Definitions
    •  Scan Tool Output Controls

Circuit/System Verification

  1. Verify that DTCs P0117 or P0118 are not set.
  2. If any of the DTCs are set, refer to DTC P0117 or P0118 for further diagnosis.
  3. Operate the vehicle within the conditions for running the DTC. DTC P1114 or P1115 should not set.
  4. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data List.

Circuit/System Testing

  1. Start the engine. Observe the engine coolant temperature (ECT) sensor parameter while moving the harness connector of the sensor. The ECT sensor parameter should not change abruptly.
  2. If the ECT sensor parameter changes abruptly, repair the harness connector of the ECT sensor.
  3. Engine running, observe the ECT sensor parameter while moving the harness connector of the ECM. The ECT sensor parameter should not change abruptly.
  4. If the ECT sensor parameter changes abruptly, repair the harness connector of the ECM.
  5. Engine running, observe the ECT sensor parameter while moving the wiring harness between the sensor and ECM. The ECT sensor parameter should not change abruptly.
  6. If the ECT sensor parameter changes abruptly, repair the wiring harness.

Component Testing

  1. Ignition OFF, disconnect the harness connector of the ECT sensor.
  2. Important: A thermometer can be used to the used to test the sensor off the vehicle.

  3. Test the ECT sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.
  4. If the resistance vs. temperature is not within 5 percent, replace the ECT sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Engine Coolant Temperature Sensor Replacement
    •  Control Module References for ECM replacement, setup, and programming