P0687 — ECM/PCM Power Relay Control Circuit High #

The wording of this code may vary depending on the vehicle manufacturer.

• ECM/PCM Power Relay Control Circuit High (General)
• Engine Control Module Power Relay Control Circuit High (Ford, GM, Toyota, Honda…)
• ECU Power Relay Control Circuit High (Nissan, Hyundai, Kia…)

Summary of Code P0687 #

P0687 is an OBD-II diagnostic trouble code indicating that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an abnormally high voltage condition in the power relay control circuit. In simpler terms, the system responsible for supplying power to your car’s main computer is not behaving as expected, with the voltage measured being higher than the normal operational range. This code is a universal alert, but the specifics may differ depending on the Original Equipment Manufacturer (OEM) in question. If left unaddressed, this problem can cause unexpected engine performance issues or even prevent the vehicle from starting.

Understanding and resolving this code is important, not just for keeping annoying warning lights at bay, but also for ensuring the reliability and safety of your vehicle’s operation. A high signal in this circuit often points to an electrical issue that could impact engine management.

Common Symptoms for Trouble Code P0687 #

When P0687 appears, your vehicle may or may not show obvious symptoms beyond an illuminated Check Engine Light. However, depending on the severity and the make/model, you could notice a range of behaviors that might seem unrelated at first glance. Here’s what to watch out for:

• Check Engine Light or Malfunction Indicator Light (MIL) is on
• Engine cranks but does not start
• Engine may stall unexpectedly
• Intermittent or no power to the ECM/PCM
• Loss of communication with other onboard control modules
• Electrical accessories may malfunction

Probable Causes for Code P0687 #

Like an electrical detective, tracking down the true cause of P0687 requires considering several usual suspects. The most common root causes, listed in order of frequency, are:

1. Faulty ECM/PCM power relay — The relay itself may have failed internally, causing an abnormal high signal.
2. Wiring issues (short to voltage, open circuit, corrosion) — Damaged or corroded wires and connectors can disrupt proper voltage control.
3. Defective ECM/PCM — Rare, but possible if the module is not processing signals correctly.
4. Blown fuse related to the ECM/PCM power supply — A fuse protecting the circuit may have failed due to overcurrent.
5. Poor ground connection — A weak or corroded ground can create voltage irregularities in the control circuit.

Step-by-Step Diagnosis for P0687 #

Diagnosing P0687 can feel like untangling a complex web, but following a structured process makes it manageable, even for less-experienced technicians. Here’s how to proceed:

• Confirm the code with a reliable OBD-II scanner; clear and see if it returns after a short drive.
• Visually inspect the ECM/PCM power relay for signs of overheating, corrosion, or physical damage.
• Check all wiring and connectors between the relay, ECM/PCM, and battery for damage, corrosion, or loose connections.
• Test the relay operation using a multimeter or relay tester to verify it activates and deactivates as commanded.
• Inspect and test all related fuses in the ECM/PCM power circuit.
• Verify the ground connections at the ECM/PCM and relay—clean and tighten if necessary.
• If all else fails, test the ECM/PCM itself for internal faults (OEM procedures advised).

Possible Repairs for Code P0687 #

Once you’ve identified the source, repairs for P0687 usually involve addressing the electrical root cause. Here’s what might be needed:

• Replace the ECM/PCM power relay if found defective.
• Repair or replace damaged wiring or connectors in the affected circuit.
• Replace any blown fuses protecting the ECM/PCM power supply.
• Clean and secure all ground connections in the circuit.
• Replace the ECM/PCM only if confirmed faulty by OEM diagnostic tests (rare).

Can You Drive with Code P0687? #

No, it is not recommended to drive with P0687 active. While some vehicles may continue to operate temporarily, the risk of sudden stalling, loss of power, or inability to restart the engine is high. This can leave you stranded or, worse, create an unsafe situation if the engine quits while driving. Address this code promptly to avoid potential breakdowns and additional electrical damage.

Vehicles Most Commonly Affected by P0687 #

While P0687 is a generic OBD-II code, it is more frequently reported on certain makes and models, often due to similar relay or wiring designs. Vehicles where this code is often encountered include:

• Ford (F-150, Focus, Escape, Fusion)
• Chevrolet (Silverado, Malibu, Cruze)
• Honda (Accord, Civic, CR-V)
• Nissan (Altima, Sentra, Rogue)
• Hyundai (Elantra, Sonata, Tucson)
• Kia (Optima, Forte, Sorento)
• Toyota (Camry, Corolla, RAV4)

Common Mistakes & Best Practices for P0687 #

Misdiagnosis is surprisingly common with code P0687, often leading to unnecessary part replacements or persistent electrical gremlins. Here are the pitfalls to avoid, and some best practices:

• Replacing the ECM/PCM without thoroughly testing the relay and wiring first
• Overlooking poor ground connections, which can mimic relay failure
• Ignoring signs of water intrusion or corrosion in the relay box
• Not checking for related codes that may point to a shared root cause
• Using non-OEM relays or parts that may not meet the vehicle’s specifications

Express FAQ for Code P0687 #

Got a burning question? Here are concise answers to the most frequent queries about P0687:

• Q: Will clearing the code fix my problem?
  A: No. Clearing the code may turn off the light temporarily, but if the underlying issue isn’t corrected, the code will return.
• Q: Can a low battery cause P0687?
  A: While not common, low system voltage or battery issues can contribute to power relay problems. Always check battery health during diagnosis.
• Q: Is this a job for a DIYer or should I see a pro?
  A: If you’re comfortable with basic electrical testing and relay replacement, you may attempt it. For anything involving module diagnostics or complex wiring, a professional technician is recommended.