Technical Description of OBD-II Trouble Code
Correlation between Engine Coolant Temperature Sensor 1/2
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is applicable to all OBD-II vehicles, including Mazda, Land Rover, GMC, Chevy, Ford, Dodge, Chrysler, Toyota, Honda, etc. The specific repair steps may vary depending on the make and model, despite being a generic code.
If a code P011A is stored in an OBD-II vehicle, it indicates that the powertrain control module (PCM) has detected an issue with the signals correlating between two separate engine coolant temperature (ECT) sensors.
These sensors are designated as A and B, or primary and secondary. This code is only used in vehicles with multiple ECT sensors.
ECT sensors are typically composed of a thermal resistor surrounded by a durable resin in a brass, aluminum, or plastic housing. The housing is designed to thread into various parts of the engine. The ECT sensor is positioned so that engine coolant can flow across the tip once the thermostat has opened. The exposed resistor is located in the tip of the sensor.
As the engine coolant temperature increases, the resistance in the ECT resistor decreases, allowing the circuit voltage to increase. The PCM recognizes these voltage variations as changes in engine coolant temperature.
The ECT sensor/s provide data to the PCM for drivability strategy, electronic cooling fan operation, and may also send a signal to the temperature gauge in the instrument cluster.
If the PCM detects independent voltage signals from the separate ECT sensors that differ by more than a preprogrammed degree, it will store a code P011A and may illuminate a malfunction indicator lamp (MIL). Certain models may require multiple failure cycles for MIL illumination.
What is the severity of this code?
Considering that engine drivability, electronic cooling fan operation, and temperature gauge accuracy can be affected by the conditions leading to a stored code P011A, it should be considered severe.
What are some of the symptoms of the code?
Symptoms of a P011A engine code may include:
What are some of the possible causes of the code?
Possible causes for this code may include:
What are some P011A troubleshooting steps?
Before attempting to diagnose a code P011A, it is recommended to have access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable vehicle information source.
Prior to diagnosing any ECT sensor related code, ensure that the engine cooling system is filled to the proper level with the correct coolant. Verify that the thermostat, water pump, radiator, and cooling fans are all functioning as intended by operating the engine. Additionally, check for any air pockets in the cooling system. The engine cooling system must be in proper working order before diagnosing this code.
Once the cooling system is operating normally, visually inspect all system wiring and connectors, and make any necessary repairs.
Next, connect the scanner to the vehicle diagnostic port and retrieve all stored codes and freeze frame data. Freeze frame data provides a snapshot of the exact circumstances at the time of the failure that led to the stored code P011A. It is advisable to write down this information for future reference. Clear the codes and test-drive the vehicle to see if the code is reset.
If the code is set before the PCM enters readiness mode, use the DVOM to test the individual ECT sensors. Any ECT sensor that fails the manufacturer’s recommended test should be replaced. Consult the vehicle information source for testing specifications.
If all ECT sensors comply with the manufacturer’s specifications, test the individual system circuits using the DVOM and make any necessary repairs.
If all sensors and circuits are in working order, suspect PCM failure or a PCM programming error.
Additional diagnostic notes:
