P0686 Engine/Transmission Control Module (ECM/PCM) Power Relay Control Circuit Low
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P0686 – OBD-II Trouble Code Technical Description
Trouble code P0686 indicates that the engine control module (ECM) or powertrain control module (PCM) power relay control circuit voltage is too low (compared to the manufacturer's specifications).
What does the fault code mean P0686?
Trouble code P0686 indicates that too low voltage is detected in the Engine Control Module (ECM) or Powertrain Control Module (PCM) power relay control circuit. This means that the electrical system responsible for supplying power to the ECM or PCM is experiencing problems with voltage that may not be sufficient for these devices to function properly.
Possible reasons
Trouble code P0686 may be caused by the following possible causes:
- Weak or dead battery: Insufficient battery voltage can cause the power relay control circuit to not operate properly.
- Poor connection or break in wires: Damaged wires or poor connections can cause insufficient voltage in the control circuit.
- Defective Power Relay: A faulty or damaged power relay may not provide enough voltage to operate the ECM or PCM.
- Grounding Problems: Insufficient or poor grounding can also cause low voltage in the control circuit.
- Defective ECM or PCM: The Engine Control Module (ECM) or Powertrain Control Module (PCM) itself may be faulty and require replacement.
- Electrical Noise: Sometimes electrical noise can interfere with the normal functioning of the control circuit and cause P0686.
- Ignition switch problems: If the ignition switch is not working correctly, it may cause insufficient voltage in the control circuit.
What are the symptoms of a fault code? P0686?
Symptoms for DTC P0686 may include the following:
- Problems with starting the engine: Low voltage in the power relay control circuit may make the engine difficult or even impossible to start.
- Loss of power: Incorrect or insufficient power supply to the ECM or PCM may result in loss of engine power or unstable operation.
- Check Engine Light Appears: Code P0686 activates the Check Engine light on the dashboard, indicating problems with the electrical system.
- Unstable engine performance: Insufficient voltage may cause the engine to run erratically, such as shaking, shaking or jerking when driving.
- Problems with electrical components: The vehicle's electrical components, such as lights, heaters, or climate control, may not operate properly.
- Loss of functions in the car: Some vehicle functions that depend on the ECM or PCM may not operate properly or be unavailable due to insufficient power.
- Speed Limit: In some cases, the vehicle may go into limited speed mode due to electrical system problems caused by code P0686.
If you experience any of these symptoms, it is recommended that you contact a qualified technician for diagnosis and troubleshooting.
How to diagnose a fault code P0686?
The following approach is recommended to diagnose DTC P0686:
- Battery check: Check the battery for sufficient charge. Use a voltmeter to measure battery voltage. Normal voltage should be around 12 volts. If the voltage is below this value, the battery may be weak or defective.
- Checking wiring and connections: Carefully inspect the wiring and connectors in the power relay control circuit. Make sure the wires are intact, not broken, and well connected. Particular attention should be paid to places where wires may be damaged or the insulation may be stripped.
- Checking the power relay: Check the condition and functionality of the power relay. It should click when the ignition is turned on. If a relay does not operate or operates unreliably, it may be faulty and require replacement.
- Grounding check: Check the grounding condition of the system. Make sure all contacts are well grounded and there is no corrosion on the contacts.
- Scanning error codes: Use a scan tool to read error codes in the ECM or PCM. In addition to the P0686 code, other codes may also be detected that can help determine the cause of the problem.
- Checking voltage to ECM/PCM: Measure the voltage at the ECM or PCM input to ensure it meets manufacturer specifications.
- Checking the ignition switch: Check the operation of the ignition switch. Make sure it supplies enough voltage to the power relay when in the on position.
After completing these steps, you will be able to more accurately determine the cause of the P0686 trouble code and take the necessary steps to correct the problem. If you do not have experience working with vehicle electrical systems, it is recommended that you contact a qualified automotive technician for further diagnosis and repair.
Diagnostic errors
When diagnosing DTC P0686, the following errors may occur:
- Skipping Basic Checks: Some technicians may skip basic diagnostic steps such as checking the battery or checking connections, which can lead to incorrect conclusions or omissions.
- Incorrect interpretation of error code: Understanding the meaning of the P0686 code may not be correct or accurate enough, which may lead to misdiagnosis and incorrect repair actions.
- Replacing components without adequate diagnostics: Sometimes technicians may jump straight into replacing components such as the power relay or ECM/PCM without conducting sufficient diagnostics, which can result in unnecessary parts costs and incorrect repairs.
- Ignoring related problems: Trouble code P0686 may be related to other problems in the vehicle's electrical system, such as corroded contacts, damaged wires, or a faulty ignition switch. Ignoring these related problems may result in the error code reoccurring after repair.
- Faulty diagnostic tools: Using faulty or uncalibrated diagnostic tools may result in incorrect diagnostic results.
- Lack of understanding of the electrical system: Inadequate understanding of the vehicle's electrical system can lead to incorrect diagnosis and repairs, especially for complex electrical problems.
To successfully diagnose and repair P0686, it is important to follow diagnostic procedures, including basic steps, and have sufficient experience and understanding of your vehicle's electrical systems.
How serious is the fault code? P0686?
Trouble code P0686, although it indicates a problem in the vehicle's electrical system, is usually not critical or directly safety threatening. However, it can lead to a number of problems that may affect the normal functioning and performance of your vehicle. Here are some factors to consider:
- Inability to start the engine: If the low voltage problem in the power relay control circuit becomes severe, it may cause the engine to be unable to start or difficult to start.
- Loss of power and unstable engine operation: Insufficient ECM or PCM power can cause loss of engine power or rough operation, which in turn can affect performance and fuel economy.
- Limitation of vehicle functions: Some vehicle functions that are dependent on the ECM or PCM may not be available or function properly due to problems with the electrical system.
- Recurrence of other error codes: Problems with the electrical system can cause other error codes to appear, which can make the situation worse and require additional diagnosis and repair.
Although the P0686 code is not an emergency, it still requires careful attention and timely repair to avoid further problems and keep your vehicle functioning properly. If you notice this error code on your vehicle, it is recommended that you contact a qualified automotive technician for diagnosis and repair.
What repair will help eliminate the code? P0686?
Resolving the P0686 trouble code may require several possible repair actions, depending on the specific cause of the problem, some of them are:
- Battery Replacement: If the problem is caused by insufficient battery power, replacing it may solve the problem. You need to make sure that the new battery has the correct specifications for your vehicle.
- Repair or replacement of wiring and connectors: If damaged wires or poor connections are found, they should be repaired or replaced. It is also important to ensure that the wires are connected correctly.
- Replacing the power relay: If the power relay does not work properly, it should be replaced with a new one. Make sure the replacement relay has the correct specifications for your vehicle.
- Checking and improving grounding: Check the system grounding and make sure the contacts are clean and properly grounded. Additional measures may be required to improve grounding.
- Overhaul or replace the ECM/PCM: If the voltage problem cannot be corrected by other means, the ECM or PCM may require repair or replacement. This usually requires specialized equipment and skills and can be an expensive repair.
- Additional diagnostic and repair actions: Sometimes the problem may be more complex and require additional diagnostic and repair steps, such as checking the ignition switch or other electrical system components.
It is important to have the cause of the P0686 code professionally diagnosed before attempting repairs. If you do not have the necessary skills and experience, it is recommended that you contact a qualified automotive technician.
P0686 – Brand-specific information
Trouble code P0686 can occur on cars of various makes and models, a list of some car brands with their meanings:
- Volkswagen (VW): For Volkswagen, this code may indicate problems with the power relay control circuit.
- Ford: For Ford, this code can also be related to problems in the power relay control circuit that supplies power to the engine control module (ECM).
- Chevrolet: On Chevrolet vehicles, the P0686 code may indicate low voltage on the power relay control circuit.
- Toyota: For Toyota, this code may indicate problems with the ECM or PCM power supply.
- BMW: For BMW, this code may indicate problems with the power supply to the engine control module.
- Mercedes-Benz: On Mercedes-Benz vehicles, the P0686 code may indicate problems with the power relay control circuit or ECM/PCM power.
- Audi: For Audi, this code may be due to insufficient voltage in the power relay control circuit.
- Honda: On a Honda, this code may indicate a problem with the ECM or PCM power supply.
- Nissan: On Nissan vehicles, this code may indicate problems with the electrical system supplying power to the PCM or ECM.
- Hyundai: For Hyundai, this code may indicate problems with the power relay or the ECM/PCM power circuit.
This is just a small list of vehicle brands that may experience trouble code P0686. It is important to note that the causes and solutions to this problem may vary slightly depending on the specific model and year of the vehicle. For accurate diagnosis and repair, it is recommended to contact a certified car service center or dealer of the selected brand.
