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 provides an overview of each diagnostic category.

DTC Descriptors

DTC P0117:  Engine Coolant Temperature (ECT) Sensor 1 Circuit Low Voltage

DTC P0118:  Engine Coolant Temperature (ECT) Sensor 1 Circuit High Voltage

DTC P2184:  Engine Coolant Temperature (ECT) Sensor 2 Circuit Low Voltage

DTC P2185:  Engine Coolant Temperature (ECT) Sensor 2 Circuit High Voltage

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

ECT Sensor 1 Signal

P0117

P0118

P0118*

P0116

ECT Sensor 1 Low Reference

--

P0118

P0118*

P0116

ECT Sensor 2 Signal

P2184

P2185

P2185*

P2183

ECT Sensor 2 Low Reference

--

P2185

P2185*

P2183

* 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 1 Signal

168°C (334°F)

-40°C (-40°F)

-40°C (-40°F)*

ECT Sensor 1 Low Reference

--

-40°C (-40°F)

-40°C (-40°F)*

ECT Sensor 2 Signal

168°C (334°F)

-40°C (-40°F)

-40°C (-40°F)*

ECT Sensor 2 Low Reference

--

-40°C (-40°F)

-40°C (-40°F)*

* ECM or sensor 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 powertrain control module (PCM) 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

P0117 and P2184

    • The engine is running for greater than 2 minutes.
    • The ignition has been off for greater than 10 minutes before the vehicle is started.
    • This DTC runs continuously when the above condition is met.

P0118 and P2185

    • The engine is running for greater than 2 minutes.
    • The intake air temperature (IAT) sensor 1 is greater than 15°C (59°F).
    • This DTC runs continuously when the above condition is met.

Conditions for Setting the DTC

P0117

The PCM detects that the ECT sensor 1 is greater than 149°C (300°F).

P0118

The PCM detects that the ECT sensor 1 is less than -38°C (-34°F).

P2184

The PCM detects that the ECT sensor 2 is greater than 149°C (300°F).

P2185

The PCM detects that the ECT sensor 2 is less than -38°C (-34°F).

Action Taken When the DTC Sets

    • DTCs P0117, P0118, P2184, P2185 are Type A DTCs.
    • The cooling fans will be commanded ON by the PCM.

Conditions for Clearing the MIL/DTC

DTCs P0117, P0118, P2184, P2185 are Type A DTCs.

Diagnostic Aids

    • After starting the engine, the ECT sensor temperature should rise steadily, then stabilize after the thermostat opens.
    • 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 IAT sensor values should display within 3°C (5°F).

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

    •  Powertrain 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. Engine idling, DTC P0117, P0118, P2184, or P2185 should not set.
  2. 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 List.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the appropriate ECT sensor.
  2. Ignition ON, clear the DTC information with a scan tool.
  3. Ignition ON, verify that the scan tool ECT sensor parameter is at -40°C (-40°F).
  4. If greater than the specified value, test the signal circuit for a short to ground. If the circuit tests normal, replace the PCM.
  5. Test for less than 0.5 volt between the low reference circuit and ground.
  6. If greater than the specified value, test the low reference circuit for a short to voltage. If the circuit/connections test normal, replace the PCM.
  7. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.
  8. If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit/connections test normal, replace the PCM.
  9. Ignition ON, clear the DTC information with a scan tool.
  10. Important: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

  11. Install a 1A fused jumper wire between the signal circuit and the low reference circuit. Verify the ECT sensor parameter is greater than 128°C (262°F).
  12. If less than the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit test normal, replace the PCM.
  13. If all circuits test normal, test or replace the appropriate ECT sensor.

Component Testing

  1. Ignition OFF, disconnect the harness connector of the appropriate 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 - Intake Air Temperature Sensor 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
    •  Powertrain Control Module Replacement for PCM replacement, setup, and programming