P0686

ECM/PCM Power Relay Control Circuit Low

Power supply / ECM relay Generic OBD-II High

What it means

P0686 means the engine computer detects a low-voltage fault in the control circuit for its own main power relay. Because this relay feeds power to the ECM/PCM and related systems, a fault here can cause hard starting, a no-start, or sudden stalling along with scattered electrical codes. It is worth treating as urgent.

High

Can I keep driving? Risky — this circuit powers the engine computer, so it can cause a no-start, sudden stalling, or intermittent electrical faults. Address it promptly.

Real-world scan data

Seen in

408

scans in the past year

Found in

0.1%

of scans

0.1%

of scans that found faults

Appears alongside · share of P0686 scans

P068Ain 49.0% of scans

P1218in 25.2% of scans

P0562in 24.8% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on, sometimes with other electrical warning lights
Hard starting or a no-start condition
Sudden or intermittent stalling
Multiple unrelated sensor codes appearing together

Common causes

Most likely first

Faulty ECM/PCM main power relayLikely
Short to ground or open in the relay control wiringCommon
Blown fuse or corroded connector in the power supply circuitCommon
Poor ground or, less often, an internal ECM/PCM driver faultLess often

How to diagnose & fix

Work through it in order

Scan for all stored codes and check the relay and its fuse first.
Test the relay control circuit for a short to ground or an open.
Inspect connectors, grounds, and power feeds for corrosion or looseness.
Replace the relay if it fails testing; treat ECM/PCM replacement as a last resort after wiring is ruled out. Clear and re-test.

FAQ

Quick answers

Is it safe to drive with P0686?+

No — because it involves the engine computer's power supply, it can leave you stranded with a no-start or stall. Get it fixed promptly.

Can I just clear P0686?+

It will return, and the underlying relay or wiring fault can still cause a stall or no-start.

Read & clear P0686 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX