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 Descriptor

DTC P011A: Engine Coolant Temperature (ECT) Sensor 1-2 Correlation

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

ECT Sensor 1 Signal

P0117, P011A

P0118, P011A

P0118, P011A

P0116, P0128, P011A

Low Reference

--

P0118, P011A

P0118, P011A

P0128, P011A

ECT Sensor 2 Signal

P2185

P2184

P2184

P0116, P0128, P011A

Low Reference

--

P2184

P2184

P0128, P011A

Typical Scan Tool Data

ECT Sensor 1 Temperature

Circuit

Short to Ground

Open

Short to Voltage

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

ECT Sensor Signal

149°C (302°F)

-40°C (-40°F)

-40°C (-40°F)

Low Reference

--

-40°C (-40°F)

-40°C (-40°F)

ECT Sensor 2 Temperature

Circuit

Short to Ground

Open

Short to Voltage

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

ECT Sensor 2 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 is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the signal circuit and a ground for the low reference circuit. The ECM uses this rationality diagnostic to determine if the input from the ECT sensor 1 or ECT sensor 2 is skewed. The ECM will compare the temperature difference between the ECT sensor 1 and the ECT sensor 2 to determine if the temperatures are within an acceptable operating range of each other.

Conditions for Running the DTC

    • DTCs P0117, P0118, P0128, P2184, P2105 are not set.
    • The ignition is ON.
    • DTC P011A runs continuously within the enabling conditions.

Conditions for Setting the DTC

When the ECM detects a temperature difference between ECT sensor 1 and ECT sensor 2 of more than 5°C (41°F).

Action Taken When the DTC Sets

DTC P011A is a Type B DTC.

Conditions for Clearing the DTC

DTC P011A is a Type B DTC.

Diagnostic Aids

    • Inspect the ECT sensor terminals for corrosion and for engine coolant leaking through the sensor. Engine coolant that is leaking through the sensor will create a high resistance short to ground. This condition results in less voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a warmer ECT.
    • This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures warmer than -8°C (+18°C), then compare those measurements to the Temperature vs Resistance table. Refer to Temperature Versus Resistance .

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. Verify that the DTCs P0117, P0118, P2184 or P2185 are not set.
  2. If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .
  3. If the ignition has been OFF for 10 hours or more, the ECT sensor  1 and the ECT sensor 2 should be within 5°C (41°F) of each other, and also the ambient temperature. Turn ON the ignition, with the engine OFF, and use a scan tool to observe the ECT sensor 2 and the ECT sensor 1 parameters. Compare those sensor parameters to each other, and to the ambient temperature. A comparison between ambient temperature and the coolant temperature sensors will determine which ECT is skewed.
  4. A quick comparison between ECT sensor 1 and ECT sensor 2 can be made at any time to determine which sensor is skewed.
  5. 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

Important: If you are unable to determine which ECT sensor is skewed, you must perform Circuit/System Verification first.

  1. Ignition OFF, disconnect the harness connector at the affected ECT sensor.
  2. Ignition OFF for 90 seconds, test for less than 5 ohms of resistance between the low reference circuit terminal A 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 parameter is colder than -39°C (-40°F).
  5. If greater than the specified range, test the signal circuit terminal B 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 B and the low reference circuit terminal A. Verify the scan tool ECT parameter is warmer than 149°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.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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