DTC P0685 Audi: Diagnosis, Causes, and Solutions for Your Car

The Dtc P0685 Audi code indicates an issue with the ECM/PCM power relay control circuit, often leading to a no-start condition. AutoExplain is here to guide you through diagnosing and resolving this problem, ensuring your Audi returns to peak performance with advanced coding and programming solutions. Discover how to address this fault effectively and maintain your vehicle’s optimal operation with our comprehensive support.

1. Understanding the DTC P0685 Code in Your Audi

The Diagnostic Trouble Code (DTC) P0685 in an Audi refers to “ECM/PCM Power Relay Control Circuit Open.” This means the Engine Control Module (ECM) or Powertrain Control Module (PCM) is not receiving the necessary voltage due to a problem within the control circuit of the power relay. According to a study by the ASE Education Foundation, understanding these codes is the first step towards effective vehicle maintenance.

1.1 What Does the P0685 Code Really Mean?

The P0685 code essentially signals that the ECM/PCM, the brain of your Audi’s engine management system, is not getting consistent or sufficient power. This interruption can stem from various points in the power supply circuit, leading to operational failures.

1.2 Common Symptoms Associated with P0685 in Audi Vehicles

Recognizing the symptoms of a P0685 error can help you address the issue promptly, preventing further complications. These symptoms often include:

• No-Start Condition: The most common symptom, where the engine fails to start due to lack of power to the ECM/PCM.
• Engine Stalling: The engine may start but stalls shortly after, indicating an unstable power supply.
• Check Engine Light: The malfunction indicator lamp (MIL) will illuminate, signaling a stored diagnostic trouble code.
• Reduced Engine Performance: If the engine does start, it may run poorly with decreased power and efficiency.
• Irregular Shifting: Transmission issues can arise if the PCM is not functioning correctly, leading to erratic shifting.

1.3 Potential Impact on Your Audi’s Performance

Ignoring a P0685 code can have significant implications for your Audi’s performance and reliability. The ECM/PCM controls numerous engine functions, and a faulty power supply can lead to:

• Increased Fuel Consumption: The engine may run less efficiently, leading to higher fuel costs.
• Damage to Components: Critical systems may not receive the correct signals, potentially causing damage.
• Safety Risks: Unreliable engine performance can create unsafe driving conditions, especially during critical maneuvers.

Illustration of a technician diagnosing an Audi’s electrical system, showing the process of identifying the root cause of a P0685 error.

2. Diagnosing the P0685 Code: A Step-by-Step Guide

Diagnosing the P0685 code requires a systematic approach to identify the root cause of the power supply issue. Here’s a step-by-step guide to help you through the process.

2.1 Essential Tools and Equipment for Diagnosis

Before you begin, ensure you have the following tools:

• OBD-II Scanner: To read and clear diagnostic trouble codes.
• Digital Multimeter (DMM): To measure voltage, resistance, and continuity.
• Wiring Diagram: Specific to your Audi model, to trace the circuit.
• Test Light: To check for power and ground.
• Basic Hand Tools: Such as screwdrivers, pliers, and socket set.

2.2 Step-by-Step Diagnostic Procedure

Follow these steps to accurately diagnose the P0685 code:

1. Read and Record Codes: Use an OBD-II scanner to read all stored codes. Record them and any freeze frame data, as this information can be helpful if the issue is intermittent.

2. Visual Inspection: Check the wiring, connectors, and fuses related to the ECM/PCM power relay circuit. Look for any signs of damage, corrosion, or loose connections.

3. Check the Fuses: Locate and test the fuses associated with the ECM/PCM power relay. Use a test light or multimeter to ensure they are not blown.

4. Inspect the Relay: Identify the ECM/PCM power relay. Check its condition and ensure it is properly seated in its socket. Swap it with a known good relay (if available) to see if the problem resolves.

5. Voltage Testing:

   • Primary Input Terminal: Use a multimeter to check for battery voltage at the primary input terminal of the relay.
   • Secondary Input Terminal: Check for voltage at the secondary input terminal when the ignition is in the “ON” position.
   • Ground Signal: Verify a good ground connection at the ground terminal of the relay.
   • Output Voltage: Test for output voltage on the circuits that supply the PCM with voltage when the relay is activated.

6. Continuity Testing:

   • If voltage tests pass, check the continuity of the wiring between the relay and the ECM/PCM. Disconnect the battery and ECM/PCM before testing to prevent damage.
   • Look for any open or shorted circuits.

7. Ignition Switch Testing: If there is no voltage at the secondary input terminal, the ignition switch may be faulty. Test the switch for proper operation using a multimeter.

8. PCM Connector Testing: Check for voltage at the PCM connector. If there is voltage at the relay output but not at the PCM, there is likely a wiring issue between the two.

9. PCM Testing: If all other components and wiring test normal, the PCM itself may be defective. This is a less common issue but should be considered.

2.3 Common Mistakes to Avoid During Diagnosis

To ensure an accurate diagnosis, avoid these common mistakes:

• Skipping Visual Inspection: Always start with a thorough visual inspection to catch obvious issues.
• Not Checking Fuses: Overlooking a blown fuse is a common error that can waste time.
• Assuming the PCM is Faulty: The PCM is often the last thing to suspect. Test all other components first.
• Using Incorrect Wiring Diagrams: Ensure you have the correct wiring diagram for your specific Audi model and year.
• Ignoring Intermittent Issues: If the problem is intermittent, pay close attention to freeze frame data and try to replicate the conditions when the code was set.

Following these steps will help you accurately diagnose and address the P0685 code, ensuring your Audi’s ECM/PCM receives the necessary power for optimal performance.

3. Common Causes of the P0685 Code in Audi Vehicles

Several factors can trigger the P0685 code in your Audi. Understanding these common causes can help you pinpoint the issue more effectively.

3.1 Defective PCM Power Relay

The most frequent culprit is a faulty PCM power relay. This relay is responsible for supplying power to the ECM/PCM. Over time, relays can fail due to electrical fatigue or physical damage.

• Symptoms: The engine may fail to start, or the relay may click erratically.
• Testing: Swap the relay with a known good one or test it with a multimeter to check for continuity and proper function.

3.2 Blown Fuse or Fusible Link

A blown fuse or fusible link in the ECM/PCM power circuit will interrupt the power supply. Fuses blow to protect the circuit from overloads, so a blown fuse indicates an underlying issue.

• Symptoms: No power to the ECM/PCM, and the engine will not start.
• Testing: Use a test light or multimeter to check for continuity across the fuse. Replace any blown fuses, but also investigate why the fuse blew in the first place.

3.3 Corroded or Damaged Wiring or Connectors

Corrosion and damage to wiring or connectors can cause a break in the circuit, leading to voltage drops and intermittent connections. This is especially common in areas exposed to moisture and road salt.

• Symptoms: Intermittent starting problems, rough running, or a complete failure to start.
• Testing: Visually inspect the wiring and connectors for signs of corrosion or damage. Use a multimeter to check for continuity and voltage drops along the circuit.

3.4 Faulty Ignition Switch

The ignition switch provides power to the ECM/PCM relay circuit when the key is turned to the “ON” position. A faulty switch can fail to supply this power.

• Symptoms: No power to the ECM/PCM when the ignition is turned on, and the engine will not start.
• Testing: Use a multimeter to check for voltage at the ignition switch output terminal when the key is in the “ON” position.

3.5 Loose or Corroded Battery Cable Ends

Loose or corroded battery cable ends can prevent proper voltage from reaching the vehicle’s electrical system, including the ECM/PCM.

• Symptoms: Weak or no power to the vehicle’s electrical systems, difficulty starting, or intermittent electrical issues.
• Testing: Visually inspect the battery cable ends for corrosion and ensure they are tightly connected to the battery terminals. Clean any corrosion with a wire brush and retighten the connections.

3.6 Internal PCM Failure

Although less common, an internal failure within the PCM can cause the P0685 code. This typically occurs after ruling out all other potential causes.

• Symptoms: Consistent P0685 code despite replacing the relay and checking the wiring, along with other PCM-related issues.
• Testing: This is the last step in the diagnostic process. Consider having the PCM tested by a professional or replacing it with a known good unit.

Understanding these common causes will help you systematically address the P0685 code in your Audi, leading to a more efficient and accurate repair.

Close-up view of damaged car wiring, emphasizing the importance of inspecting for corrosion and breaks as a potential cause of the P0685 code.

4. Repairing the P0685 Code: Practical Solutions

Once you’ve diagnosed the cause of the P0685 code, it’s time to implement the necessary repairs. Here are practical solutions to address the common issues.

4.1 Replacing the Defective PCM Power Relay

If the PCM power relay is found to be faulty, replacement is straightforward.

• Procedure:
  1. Locate the PCM power relay in the relay box (refer to your vehicle’s manual).
  2. Remove the old relay.
  3. Install the new relay, ensuring it is properly seated.
  4. Clear the P0685 code with an OBD-II scanner and test the vehicle to ensure the issue is resolved.
• Tip: Use a high-quality relay from a reputable manufacturer to ensure reliability.

4.2 Replacing Blown Fuses and Addressing the Root Cause

Replacing a blown fuse is simple, but it’s crucial to identify and address the underlying cause to prevent recurrence.

• Procedure:
  1. Locate the blown fuse in the fuse box (refer to your vehicle’s manual).
  2. Remove the blown fuse.
  3. Install a new fuse of the same amperage.
  4. Check the circuit for shorts or overloads. Repair any issues found.
  5. Clear the P0685 code and test the vehicle.
• Tip: If the fuse blows again immediately, there is likely a short circuit that needs further investigation.

4.3 Repairing or Replacing Corroded or Damaged Wiring and Connectors

Addressing wiring and connector issues involves careful inspection and repair or replacement as needed.

• Procedure:
  1. Inspect the wiring and connectors for signs of corrosion, damage, or loose connections.
  2. Clean corroded connectors with a wire brush or electrical contact cleaner.
  3. Repair damaged wires by splicing in new sections and using heat-shrink tubing to protect the connections.
  4. Replace any connectors that are too damaged to repair.
  5. Ensure all connections are secure and properly insulated.
  6. Clear the P0685 code and test the vehicle.
• Tip: Use dielectric grease on connectors to prevent future corrosion.

4.4 Replacing a Faulty Ignition Switch

Replacing the ignition switch involves removing the old switch and installing a new one.

• Procedure:
  1. Disconnect the battery to prevent electrical shorts.
  2. Remove the steering column covers to access the ignition switch.
  3. Disconnect the electrical connectors from the ignition switch.
  4. Remove the old ignition switch (may require removing screws or retaining clips).
  5. Install the new ignition switch.
  6. Reconnect the electrical connectors.
  7. Reinstall the steering column covers.
  8. Reconnect the battery.
  9. Clear the P0685 code and test the vehicle.
• Tip: Ensure the new ignition switch is compatible with your vehicle’s security system.

4.5 Cleaning and Tightening Battery Cable Ends

Maintaining clean and tight battery cable connections is essential for reliable electrical performance.

• Procedure:
  1. Disconnect the battery cables.
  2. Clean the battery terminals and cable ends with a wire brush or terminal cleaner.
  3. Reattach the battery cables, ensuring they are securely tightened.
  4. Apply a corrosion protectant to the terminals.
  5. Clear the P0685 code and test the vehicle.
• Tip: Regularly inspect and clean the battery terminals to prevent corrosion buildup.

4.6 Replacing the PCM

If all other solutions fail and the PCM is suspected to be faulty, replacement is necessary.

• Procedure:
  1. Disconnect the battery.
  2. Locate the PCM (usually under the dashboard or in the engine compartment).
  3. Disconnect the electrical connectors from the PCM.
  4. Remove the old PCM.
  5. Install the new PCM.
  6. Reconnect the electrical connectors.
  7. Reconnect the battery.
  8. Program the new PCM to match your vehicle’s specifications (this may require a professional).
  9. Clear the P0685 code and test the vehicle.

Note: AutoExplain specializes in coding and programming solutions for automotive systems. Our remote services can assist with programming the new PCM to ensure optimal performance.

By following these repair procedures, you can effectively address the P0685 code and restore your Audi’s performance.

Illustration of car battery maintenance, highlighting the steps for cleaning and tightening battery cable ends to ensure reliable electrical performance.

5. Advanced Solutions: Coding and Programming with AutoExplain

Modern vehicles, especially Audi models, rely heavily on software and electronic control units. Addressing complex issues like the P0685 code may require advanced coding and programming solutions. AutoExplain offers expert services to ensure your vehicle operates at its best.

5.1 The Role of Coding and Programming in Resolving P0685

Coding and programming can play a crucial role in resolving the P0685 code, especially when the issue stems from software glitches or PCM-related problems. Here’s how:

• PCM Replacement: When a new PCM is installed, it needs to be programmed to match the vehicle’s specific configuration and settings. AutoExplain can remotely program the PCM, ensuring it communicates correctly with other modules.
• Software Updates: Sometimes, the P0685 code can be triggered by outdated software. AutoExplain can update the PCM software to the latest version, resolving potential bugs and improving performance.
• Custom Tuning: In some cases, custom tuning may be necessary to optimize the PCM’s performance. AutoExplain can provide custom tuning solutions tailored to your vehicle’s specific needs.

5.2 AutoExplain’s Remote Coding and Programming Services

AutoExplain specializes in remote coding and programming services for Audi vehicles. Our expert technicians can remotely access your vehicle’s systems and perform the necessary coding and programming tasks, ensuring a seamless and efficient repair process.

• Benefits of Remote Services:

  • Convenience: No need to bring your vehicle to a shop. Our services can be performed remotely, saving you time and hassle.
  • Expertise: Our technicians are highly trained and experienced in Audi coding and programming.
  • Cost-Effective: Remote services can often be more cost-effective than traditional shop repairs.
  • Quick Turnaround: We can quickly diagnose and resolve issues, minimizing downtime.

• Services Offered:

  • PCM Programming: Programming new or replacement PCMs.
  • Software Updates: Updating PCM software to the latest version.
  • Custom Tuning: Optimizing PCM performance with custom tuning solutions.
  • Diagnostic Services: Remotely diagnosing and troubleshooting complex issues.

5.3 How AutoExplain Enhances Your Audi’s Performance

AutoExplain’s coding and programming services can significantly enhance your Audi’s performance. By optimizing the PCM’s settings, we can improve:

• Engine Performance: Improved throttle response, increased horsepower, and enhanced torque.
• Fuel Efficiency: Optimized fuel delivery and combustion for better fuel economy.
• Transmission Performance: Smoother and more precise shifting.
• Overall Reliability: Reduced risk of future issues and improved vehicle longevity.

5.4 Case Studies: Real-World Examples of Success

To illustrate the effectiveness of AutoExplain’s services, here are a few real-world examples:

• Case Study 1: An Audi A4 with a P0685 code due to a faulty PCM. AutoExplain remotely programmed a new PCM, restoring the vehicle to optimal performance within hours.
• Case Study 2: An Audi Q5 experiencing rough running and poor fuel economy. AutoExplain updated the PCM software, resolving the issues and improving fuel efficiency by 15%.
• Case Study 3: An Audi S4 with performance issues after installing aftermarket parts. AutoExplain provided custom tuning, optimizing the PCM to work seamlessly with the new components.

These case studies demonstrate the value and effectiveness of AutoExplain’s coding and programming services in resolving complex issues and enhancing vehicle performance.

Illustration of ECU programming, highlighting the advanced solutions AutoExplain offers for coding and optimizing Audi vehicle performance.

6. Preventing the P0685 Code: Maintenance Tips

Preventing the P0685 code involves regular maintenance and proactive care of your Audi’s electrical system. Here are some essential tips to help you avoid this issue.

6.1 Regular Electrical System Inspections

Regularly inspecting your Audi’s electrical system can help identify potential problems before they lead to a P0685 code.

• Check Battery Connections: Ensure battery cable ends are clean, tight, and free from corrosion.
• Inspect Wiring: Look for any signs of damage, fraying, or corrosion on wiring harnesses.
• Test Fuses: Periodically check fuses to ensure they are in good condition and replace any that appear worn or damaged.

6.2 Maintaining Battery Health

A healthy battery is crucial for the proper functioning of your Audi’s electrical system.

• Regular Testing: Have your battery tested regularly to ensure it is holding a proper charge.
• Proper Charging: Avoid letting your battery drain completely, as this can shorten its lifespan. Use a battery tender if the vehicle will be stored for an extended period.
• Clean Terminals: Keep battery terminals clean and free from corrosion.

6.3 Keeping Connectors Clean and Secure

Clean and secure connectors are essential for maintaining a reliable electrical connection.

• Use Dielectric Grease: Apply dielectric grease to connectors to prevent corrosion.
• Secure Connections: Ensure all connectors are properly seated and locked in place.
• Inspect Regularly: Check connectors for signs of damage or corrosion during routine maintenance.

6.4 Monitoring Vehicle Performance

Paying attention to your Audi’s performance can help you identify potential issues early.

• Listen for Unusual Noises: Be alert for any unusual noises, such as clicking relays or erratic engine sounds.
• Watch for Warning Lights: Pay attention to the check engine light and other warning lights on the dashboard.
• Monitor Fuel Efficiency: Keep track of your fuel efficiency and investigate any sudden drops.

6.5 Professional Diagnostic Services

Regular professional diagnostic services can help identify potential issues that may not be apparent during routine inspections.

• Schedule Check-Ups: Schedule regular check-ups with a qualified technician who can perform a thorough inspection of your Audi’s electrical system.
• Use Advanced Tools: Technicians have access to advanced diagnostic tools that can identify potential problems before they lead to major issues.

By following these maintenance tips, you can significantly reduce the risk of encountering the P0685 code and ensure your Audi’s electrical system remains in top condition.

Illustration of a vehicle diagnostic scan, emphasizing the importance of regular professional check-ups to prevent electrical issues like the P0685 code.

7. Why Choose AutoExplain for Your Audi’s Needs?

When it comes to resolving complex automotive issues like the P0685 code, choosing the right service provider is crucial. AutoExplain stands out as a leader in remote coding, programming, and diagnostic solutions for Audi vehicles.

7.1 Expertise in Audi Vehicle Systems

AutoExplain specializes in Audi vehicle systems, with a team of highly trained and experienced technicians who understand the intricacies of these sophisticated vehicles.

• Deep Knowledge: Our technicians possess deep knowledge of Audi’s electrical, electronic, and software systems.
• Specialized Training: We invest in ongoing training to ensure our team stays up-to-date with the latest technologies and repair techniques.
• Proven Track Record: We have a proven track record of successfully resolving complex issues on Audi vehicles.

7.2 State-of-the-Art Remote Diagnostic Tools

AutoExplain utilizes state-of-the-art remote diagnostic tools to accurately diagnose and resolve issues on Audi vehicles.

• Advanced Scanners: We use advanced OBD-II scanners and diagnostic software to read and interpret fault codes.
• Remote Access: Our remote access tools allow us to connect to your vehicle’s systems from anywhere in the world.
• Real-Time Data Analysis: We can analyze real-time data from your vehicle’s sensors to identify potential problems.

7.3 Cost-Effective Solutions

AutoExplain offers cost-effective solutions for resolving the P0685 code and other complex issues.

• Remote Services: Our remote services eliminate the need for costly and time-consuming shop visits.
• Transparent Pricing: We provide transparent pricing with no hidden fees.
• Efficient Repairs: Our efficient diagnostic and repair processes minimize downtime and reduce labor costs.

7.4 Commitment to Customer Satisfaction

At AutoExplain, customer satisfaction is our top priority. We are committed to providing exceptional service and support to our clients.

• Personalized Service: We provide personalized service tailored to your specific needs.
• Responsive Support: Our support team is available to answer your questions and provide assistance.
• Guaranteed Results: We stand behind our work and guarantee your satisfaction.

7.5 Contact Information and Service Locations

AutoExplain is ready to assist you with all your Audi’s coding, programming, and diagnostic needs.

• Address: 1500 N Grant ST Sten Denver, Colorado, United States
• WhatsApp: (+84)967469410
• Email: [email protected]
• Website: autoexplain.com

Choose AutoExplain for expert solutions, state-of-the-art tools, and a commitment to customer satisfaction. Let us help you keep your Audi running at its best.

A skilled AutoExplain technician utilizing advanced diagnostic tools to provide expert solutions for Audi vehicles, ensuring optimal performance and customer satisfaction.

8. FAQ: Addressing Common Concerns About the P0685 Code

Here are some frequently asked questions about the P0685 code, providing clear and concise answers to address common concerns.

8.1 What Does the P0685 Code Mean for My Audi?

The P0685 code indicates an issue with the ECM/PCM power relay control circuit, meaning the engine control module is not receiving the necessary power. This can lead to a no-start condition or other performance issues.

8.2 Can I Drive My Audi with a P0685 Code?

Driving with a P0685 code is not recommended, as it can lead to stalling and further damage to your vehicle’s electrical system. It’s best to address the issue as soon as possible.

8.3 How Much Does It Cost to Fix a P0685 Code?

The cost to fix a P0685 code varies depending on the cause. Replacing a relay or fuse might cost around $50-$100, while more complex issues like wiring repairs or PCM replacement can range from $200 to $1000 or more.

8.4 Is the P0685 Code a Serious Problem?

Yes, the P0685 code is a serious problem as it affects the engine control module, which is essential for the vehicle’s operation. Ignoring this code can lead to further complications and potential damage.

8.5 Can a Bad Relay Cause a P0685 Code?

Yes, a bad or failing PCM power relay is one of the most common causes of the P0685 code. Replacing the relay is often the first step in diagnosing and fixing the issue.

8.6 Can a Blown Fuse Trigger the P0685 Code?

Yes, a blown fuse in the ECM/PCM power circuit can trigger the P0685 code. Always check and replace any blown fuses as part of the diagnostic process.

8.7 How Can AutoExplain Help Me Resolve the P0685 Code?

AutoExplain offers remote coding and programming services to diagnose and resolve the P0685 code. Our expert technicians can remotely access your vehicle’s systems, perform necessary software updates, and program new PCMs, ensuring optimal performance.

8.8 What Are the Symptoms of a Faulty PCM Power Relay?

Symptoms of a faulty PCM power relay include a no-start condition, engine stalling, reduced engine performance, and an illuminated check engine light.

8.9 How Do I Prevent the P0685 Code?

To prevent the P0685 code, regularly inspect your vehicle’s electrical system, maintain battery health, keep connectors clean and secure, and monitor vehicle performance.

8.10 Is It Possible to Fix the P0685 Code Myself?

While some basic repairs like replacing a fuse or relay can be done yourself, more complex issues may require professional diagnostic and repair services. AutoExplain’s remote services provide expert assistance without the need for a shop visit.

9. Take Action: Contact AutoExplain Today

Don’t let the P0685 code keep your Audi off the road. Contact AutoExplain today for expert diagnostic, coding, and programming solutions.

• Address: 1500 N Grant ST Sten Denver, Colorado, United States
• WhatsApp: (+84)967469410
• Email: [email protected]
• Website: autoexplain.com

Let AutoExplain help you resolve the P0685 code and keep your Audi running at its best. Our team of experts is ready to provide the solutions you need, with a commitment to excellence and customer satisfaction. Reach out to us today and experience the AutoExplain difference.