Description of the P0668 fault code.
OBD2 Error Codes

P0668 Powertrain/Engine/Transmission Control Module Internal Temperature Sensor "A" Circuit Low PCM/ECM/TCM

26.05.2022 /

P0668 – OBD-II Trouble Code Technical Description

Trouble code P0668 indicates that the powertrain control module (PCM), engine control module (ECM), or transmission control module (TCM) internal temperature sensor circuit voltage is too low (compared to the manufacturer's specification).

What does the fault code mean P0668?

Trouble code P0668 indicates that too low voltage is detected in the powertrain control module (PCM), engine control module (ECM), or transmission control module (TCM) internal temperature sensor circuit. This could mean that the temperature sensor or its wiring is faulty, or there is a problem with the control module, which could be related to engine or transmission temperature. Code P0668 usually causes the Check Engine light to appear on your vehicle's dashboard.

Fault code P0668.

Possible reasons

Trouble code P0668 can be caused by a number of potential causes:

  • Temperature Sensor Failure: The temperature sensor itself may be damaged or failed, resulting in an incorrect temperature reading and therefore a P0668 code.
  • Wiring: The wiring connecting the temperature sensor to the control module (ECM, TCM, or PCM) may be damaged, broken, or poorly connected, resulting in a low circuit voltage and an error.
  • Control Module Failure: The control module itself (ECM, TCM or PCM) may be faulty, causing the temperature sensor to not process data correctly and causing code P0668 to occur.
  • Engine or Transmission Temperature Issues: Problems with the engine cooling system or transmission cooling system can also cause P0668 because an incorrect temperature may be recorded by the sensor.
  • Improper installation or replacement of components: Improper installation of the temperature sensor or other engine/transmission control system components can also cause P0668.

To accurately determine the cause of error P0668, it is recommended to diagnose the vehicle using specialized tools and equipment.

What are the symptoms of a fault code? P0668?

Symptoms associated with DTC P0668 can vary depending on specific conditions and vehicle type, some common symptoms are:

  • Check Engine Light: The appearance of the Check Engine light on your vehicle's dashboard may be the first and foremost sign that there is a problem with the engine or transmission control system.
  • Loss of Power: There may be a loss of engine power, especially when operating at low speeds or when accelerating. This may be due to incorrect engine management system settings due to unreliable temperature data.
  • Unstable Engine Operation: The engine may run rough, idle rough, or become unstable.
  • Increased fuel consumption: Due to improper operation of the fuel management and ignition system caused by the P0668 code, fuel consumption may increase.
  • Shifting: If the problem is with the Transmission Control Module (TCM), you may experience problems shifting gears, such as delayed or jerky shifts.

These symptoms may not always be obvious and may occur to varying degrees depending on the specific situation. If you experience a Check Engine Light or any other unusual symptoms, it is recommended that you contact a qualified auto mechanic for diagnosis and troubleshooting.

How to diagnose a fault code P0668?

The following steps are recommended to diagnose DTC P0668:

  1. Check the Check Engine Light: If the Check Engine Light illuminates on your dashboard, it may be a sign of P0668. However, if the light does not come on, this does not rule out the problem, since not all cars can instantly activate the light when an error is detected.
  2. Use a diagnostic scanner: Connect the diagnostic scanner to the OBD-II port of your car. The scanner will read trouble codes, including P0668, and provide information about other parameters and sensors that can help with diagnosis.
  3. Explore additional error codes: Sometimes the P0668 code may be accompanied by other error codes that may provide more information about the problem. Check any other codes that may be registered in the system.
  4. Check wiring and connections: Check the wiring connecting the temperature sensor to the control module (ECM, TCM or PCM) for damage, corrosion or breaks. Make sure all connections are secure and free of oxidation.
  5. Check the temperature sensor: Check the condition and functionality of the temperature sensor. You may need to check the sensor resistance at different temperatures using a multimeter.
  6. Additional tests and checks: Depending on the specific vehicle type and engine management system, additional tests may include cooling system performance, oil pressure, and other parameters that may be related to engine or transmission temperature.
  7. Consult with a professional: If you are unsure of your skills or experience in diagnosing automotive systems, it is recommended that you contact a qualified auto mechanic or service center for a more detailed diagnosis and resolution of the problem.

Diagnostic errors

When diagnosing DTC P0668, the following errors may occur:

  • Determining the cause solely by the error code: The P0668 code indicates that the temperature sensor circuit voltage is too low, but it does not provide information about the specific cause of the problem. The error can be caused by a variety of factors, including a faulty sensor, wiring problems, or even a faulty control module.
  • Ignoring other symptoms and signs: Some problems associated with the P0668 code may manifest themselves through other symptoms, such as loss of power, rough running, or shifting problems. Ignoring these symptoms may result in important diagnostic information being missed.
  • Faulty component replacement: When trouble code P0668 is detected, it may be tempting to immediately replace the temperature sensor or other system components. However, this may not solve the problem if the problem lies elsewhere, such as in the wiring or control module.
  • Incorrect diagnosis and repair: Misdiagnosis can lead to unnecessary component replacement or incorrect repairs, which can be costly and time-consuming.
  • Lack of professional help: Some problems associated with the P0668 code can be difficult to diagnose and repair. Lack of experience or skills may result in ineffective or incorrect actions. In such cases, it is recommended that you contact a qualified auto mechanic or service center for assistance.

To avoid these mistakes, it is important to approach diagnosis systematically, taking into account all available symptoms and information.

How serious is the fault code? P0668?

Trouble code P0668 can be serious because it indicates a voltage problem in the temperature sensor circuit, which may affect the operation of the engine or transmission control system. Possible consequences from a P0668 code may include:

  • Loss of power: Inaccurate temperature data may result in incorrect engine management system settings, which may cause loss of power.
  • Increased fuel consumption: Incorrect fuel and ignition management due to incorrect temperature data may result in increased fuel consumption.
  • Engine damage: If the engine is not cool enough or overheated, serious problems may occur such as damage to the cylinder head, cylinder head gaskets, piston rings, etc.
  • Transmission damage: If the problem also affects transmission control, incorrect temperature data may cause incorrect gear shifting and even damage to the transmission.

Although the P0668 code can be considered serious, it is important to consider it in the context of other symptoms and factors. In some cases, it may be caused by a temporary glitch or minor defect that can be easily fixed.

What repair will help eliminate the code? P0668?

Troubleshooting the P0668 trouble code may require several possible actions depending on the specific cause of the problem. Some typical repair methods:

  • Replacing the temperature sensor: If the error is caused by a faulty temperature sensor, it may need to be replaced. It is recommended to use original spare parts or high-quality analogues to avoid further problems.
  • Checking and repairing wiring: If the cause of the error is due to damage or broken wiring, it is necessary to check and, if necessary, repair the wiring, ensuring a reliable connection between the temperature sensor and the control module.
  • Diagnostics and replacement of the control module: If all system components are working properly but P0668 still occurs, the cause may be a faulty control module (ECM, TCM or PCM). In this case, diagnostics may be required to determine the malfunction and replacement or repair of the control module.
  • Checking and fixing cooling system problems: If the cause of the error is problems with the temperature of the engine or transmission, additional diagnostics of the cooling system must be carried out. This may include checking for coolant, thermostat condition, leaks, or pump problems.
  • Programming and software updates: In some cases, the cause of the P0668 code may be problems with the control module software. Updating or reprogramming the software may help resolve the problem.

It is important to note that it is recommended that you contact a qualified auto mechanic or service center to accurately determine and correct the cause of the P0668 code, especially if you do not have experience working with automotive systems. Improper repairs or diagnosis may result in additional problems or damage.

What is P0668 Engine Code [Quick Guide]

P0668 – Brand-specific information

Trouble code P0668 can be common to many makes of cars, but its meaning and possible causes may vary slightly depending on the specific make and model, a list of several popular car brands with brief explanations of the P0668 trouble code:

This is just a small list of examples, and each car brand may have its own specific context for the P0668 code. For more accurate information, it is recommended that you consult the specific documentation, service manuals, or qualified personnel for your specific vehicle make and model.

One comment

Add a comment