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 Circuit Low Voltage

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

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

ECT Sensor Signal

P0117, P011A

P0118, P011A

P0118, P011A

P0116, P0128, P011A

Low Reference

--

P0118, P011A

P0118, P011A

P0128

Typical Scan Tool Data

ECT Sensor Temperature

Circuit

Short to Ground

Open

Short to Voltage

Operating Conditions: Engine Running

Parameter Normal Range: -39 to +120°C (-38 to +248°F)

ECT Sensor 1 Signal

149°C (300°F)

-40°C (-40°F)

-40°C (-40°F)

Low Reference

--

-40°C (-40°F)

-40°C (-40°F)

Circuit/System Description

The engine coolant temperature (ECT) sensor 1 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 a ground for the ECT low reference circuit.

Conditions for Running the DTC

P0117

    • The ignition is ON.
    • DTC P0117 runs continuously within the enabling condition.

P0118

    • The ignition is ON.
    • DTC P0118 runs continuously within the enabling condition.

Conditions for Setting the DTC

P0117

The ECM detects that the ECT Sensor 1 is warmer than 149°C (300°F) for more than 10 seconds.

P0118

The ECT sensor 1 temperature is colder than -39°C (-38°F) for more than 60 seconds.

Action Taken When the DTC Sets

DTCs P0117 and P0118 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P0117 and P0118 are Type A DTCs.

Diagnostic Aids

An ECT sensor 1 signal circuit or low reference circuit that is shorted to another 5-volt reference circuit can cause a DTC P0118 to set.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

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

Circuit/System Verification

  1. Ignition ON, observe the ECT Sensor parameter. The reading should be between -37 to +139°C (-35 to +282°F), depending on the current ambient temperature and the vehicle operating conditions.
  2. 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 data.

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the ECT sensor 1.
  2. Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the low reference circuit terminal B and ground.
  3. If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
  4. Ignition ON, verify the scan tool ECT sensor 1 parameter is colder than -39°C (-40°F).
  5. If greater than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the ECM.
  6. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool ECT Sensor 1 parameter is warmer than 148°C (300°F)
  7. If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
  8. If all circuits test normal, test or replace the ECT sensor 1.

Component Testing

Measure and record the resistance of the ECT sensor at various ambient temperatures and compare those measurements to the Temperature vs. Resistance Table. Refer to Temperature Versus Resistance.

Repair Instructions

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

Repair Verification

  1. Install any components or connectors that have been removed or replaced during diagnosis.
  2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
  3. Clear the DTCs.
  4. Turn OFF the ignition for 90 seconds.
  5. Duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset. If the DTC resets or another DTC is present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and perform the appropriate diagnostic procedure.
  6. Engine running, observe the scan tool Soot Mass parameter.
  7. If the Soot Mass value is less than 30 grams, perform the Diesel Particulate Filter (DPF) Regeneration Enable
    If the Soot Mass value is greater than 30 grams, perform the Diesel Particulate Filter (DPF) Service Regeneration