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DTC code page

P0687: ECM/PCM Power Relay Control Circuit High

Quick answer: The PCM detected the relay control circuit staying higher than expected or shorted toward power.

Drivers also search this fault as PCM power relay control high, ECM relay high input, PCM relay circuit high.

Severity: high Family: powertrain Related paths: 13
Meaning

What P0687 usually means

P0687 is the high-side version of the PCM power-relay control problem. Instead of an open or low feed, the control circuit appears stuck high, overfed, or otherwise not following the commanded state correctly. That can happen with a short to voltage, a relay stuck energized, a driver fault, or wiring that keeps back-feeding the circuit.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Ask whether the PCM or related circuits stay awake after key-off because that clue fits a stuck-high control path.
  • Inspect the relay for sticking and the socket for melted plastic or bridged terminals.
  • Check for charging or battery-drain complaints that began around the same time.
Driving risk

Can you keep driving?

P0687 can create unreliable starts, battery drain, or module-power behavior that changes from trip to trip. Diagnose it before it strands the vehicle or cooks the battery.

High urgency: If symptoms are active, reduce driving and diagnose quickly before secondary damage builds.
Likely causes

Common causes behind this code

  • Control wire shorted to battery voltage
  • PCM power relay stuck on or internally welded
  • Ignition-switch circuit back-feeding the relay control side
  • Driver fault keeping the relay commanded incorrectly
  • Fuse-box or harness damage causing unintended voltage on the control circuit

Cause phrases often tied to this code: short to power, stuck relay, backfeed, ignition switch, module driver.

Diagnostic order

Suggested workflow

  1. Review freeze-frame and note whether the fault set at startup, key-off, or during a voltage event.
  2. Verify whether the relay control side remains powered when it should not.
  3. Inspect wiring for short-to-power and fuse-box damage.
  4. Test relay behavior directly and replace it only if it fails the command and release checks.
  5. Confirm the PCM powers down correctly after the repair and the code does not return.
Avoid guesswork

Common mistakes

  • Ignoring battery-drain clues because the complaint started as a check-engine light.
  • Replacing the battery while a stuck relay keeps draining it overnight.
  • Assuming a high-circuit code cannot still be a wiring or socket problem.
Repair path

Practical fix guidance

  • Repair the short-to-power, backfeed, stuck relay, or control-driver fault proven by testing.
  • Verify normal key-off shutdown timing after the repair so the PCM is not being kept awake.
  • If battery or charging damage occurred, retest those systems separately.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0687

Useful when the driver knows the wording but not the exact DTC yet.

  • PCM power relay control high
  • ECM relay high input
  • PCM relay circuit high
Related search intent

Queries this page can answer naturally

  • P0687 code meaning
  • what does P0687 mean
  • PCM power relay control circuit high
FAQ

Quick questions about P0687

Can P0687 drain the battery?

Yes. If the relay stays energized or the PCM remains awake after shutdown, parasitic drain becomes a real possibility.

Does P0687 mean overcharging from the alternator?

Not by itself. It is more specifically about the PCM power-relay control path, though charging issues can distort the system around it.

What makes P0687 different from P0686?

P0686 points to a low-control problem, while P0687 points to a high or stuck-powered control condition.