P0687 Code: Complete DIY Repair Guide

The P0687 trouble code is an OBD-II diagnostic code that indicates a problem with the ECM/PCM (Engine Control Module/Powertrain Control Module) power relay control circuit. Specifically, this code signals that the power relay is experiencing a high voltage condition, which can lead to various operational issues in the vehicle. Understanding this code is essential for vehicle owners and DIY mechanics, as it can affect engine performance and reliability.

Symptoms of P0687 Code

When the P0687 code is triggered, several symptoms may manifest, including:

• Check Engine Light: The most common indicator is the illumination of the check engine light on the dashboard.
• Hard Start or No Start: The vehicle may exhibit difficulty starting or may not start at all, especially in cold weather.
• Decreased Engine Power: Drivers may notice a reduction in engine performance and acceleration.
• Engine Misfires: In some cases, the engine may misfire due to insufficient power being supplied to the PCM.

Understanding these symptoms is crucial for timely diagnosis and repair.

Technical Explanation

The P0687 code arises when the PCM detects an abnormal voltage level from its power supply circuit. This circuit typically includes a power relay that delivers battery voltage to the PCM. If this relay malfunctions or if there are issues within the wiring harness—such as shorts, corrosion, or damaged connectors—the PCM may receive too much voltage, leading to potential damage.

Step-by-Step Diagnosis

1. Use an OBD-II Scanner: Begin by connecting an OBD-II scanner to retrieve the P0687 code and any other stored codes.
2. Inspect Wiring and Connectors: Examine the wiring between the battery and PCM for any signs of damage or corrosion. Pay close attention to connectors and terminals.
3. Test Voltage Levels: Using a digital volt/ohmmeter (DVOM), check for proper voltage levels at the power relay and ensure they are within manufacturer specifications.
4. Check Power Relay Functionality: Test the power relay for proper operation. If it fails to click when energized or shows signs of internal damage, it may need replacement.
5. Inspect Alternator Output: Verify that the alternator is not overcharging. An overcharging alternator can send excessive voltage through the system.
6. Evaluate Ignition Switch: Ensure that the ignition switch is functioning correctly, as faults here can also cause issues with power delivery to the PCM.
7. Clear Codes and Test Drive: After repairs, clear any diagnostic trouble codes and take the vehicle for a test drive to see if the P0687 code returns.

Solution Methods

Replacing the Power Relay

If testing indicates that the power relay is faulty:

• Locate the relay in your vehicle’s fuse box (consult your owner’s manual for specific locations).
• Remove the old relay by pulling it straight out of its socket.
• Insert a new relay, ensuring it fits snugly into place.

Repairing Wiring Issues

If you find damaged wiring:

• Cut out any corroded sections of wire and splice in new wire of equal gauge.
• Use heat-shrink tubing or electrical tape to insulate connections properly.

Addressing Alternator Issues

If overcharging is detected:

• Test the alternator output with a DVOM; it should not exceed 14.5 volts while running.
• If overcharging is confirmed, replace or repair the alternator as necessary.

Ignition Switch Replacement

If diagnosed as faulty:

• Disconnect battery power before starting work.
• Remove trim panels as necessary to access the ignition switch.
• Replace with a new switch following manufacturer instructions.

Cost Estimates

The cost of repairs related to a P0687 code can vary significantly based on factors like location, vehicle make/model, and whether you perform repairs yourself or hire a professional:

• Power Relay Replacement: $20 – $100 (parts only)
• Wiring Repairs: $50 – $200 (depending on extent of damage)
• Alternator Replacement: $300 – $700 (including parts and labor)
• Ignition Switch Replacement: $100 – $300 (parts and labor)

Warnings and Recommendations

• Professional Help: If you are unsure about diagnosing or repairing electrical issues, seek assistance from a qualified mechanic. Incorrect repairs can lead to further complications.
• Monitor Symptoms: If symptoms persist after repairs, further diagnostics may be necessary to identify underlying issues not addressed during initial repairs.
• Preventative Maintenance: Regularly inspect electrical components as part of routine maintenance to prevent issues like those associated with P0687 from arising unexpectedly.

Closing Paragraph

Understanding and addressing the P0687 trouble code is vital for maintaining your vehicle’s performance and reliability. By following this guide, DIY mechanics can effectively diagnose and resolve issues related to this code, ensuring their vehicles operate safely and efficiently. Always prioritize safety when working on your vehicle’s electrical systems, and do not hesitate to consult professionals when needed.

Frequently Asked Questions About P0687

• What does P0687 mean?
  P0687 indicates that there is a high voltage condition detected in the ECM/PCM power relay control circuit.
• Can I drive my car with a P0687 code?
  While some vehicles may still run, it’s advisable not to drive until repairs are made due to potential damage to the PCM.
• How serious is a P0687 code?
  This code can lead to significant engine performance issues; therefore, it should be addressed promptly.
• What tools do I need to diagnose P0687?
  A basic OBD-II scanner and a digital volt/ohmmeter are essential for diagnosing this trouble code.
• Can I fix P0687 myself?
  If you have basic automotive knowledge and tools, many aspects of diagnosing and repairing P0687 can be done at home.
• What are common causes of P0687?
  The most common causes include faulty power relays, overcharging alternators, bad ignition switches, or damaged wiring.
• Will replacing parts always fix P0687?
  No; proper diagnosis is crucial as simply replacing parts without identifying underlying issues may not resolve the problem.
• How often does P0687 occur?
  The frequency varies by vehicle model but can occur more often in older vehicles with aging electrical systems.