ECM/PCM Power Relay Control Circuit Low
The P0686 code means the vehicle's onboard diagnostic system has detected: ECM/PCM Power Relay Control Circuit Low. This is a critical severity code.
- Keep driving?
- No — stop driving
- DIY difficulty
- hard
- Estimated cost
- $100 - $800 (parts and labor)
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What Are the Symptoms of P0686?
- Check Engine Light on
- ECM power relay circuit shorted low
- Vehicle may enter limp mode
- Possible no-start condition
What Causes P0686? (Most Likely First)
- Short to ground in ECM power relay circuit Very High
- Wiring damage or corrosion in the circuit High
- Poor electrical connection at module or component Moderate
- ECM or control module internal failure Low
Can I Still Drive with P0686?
No — stop driving. P0686 is rated critical severity. Continuing to drive in this state risks further damage — get it looked at before your next trip.
Frequently Asked Questions
What does P0686 mean?
P0686 indicates a fault in the ecm/pcm power relay control circuit low. This is an electronic control system code that affects the ECM's ability to manage the associated component or system.
Is P0686 a serious code?
Yes, this code indicates a critical control circuit issue that can affect vehicle operation and should be addressed immediately.
Can a low battery cause ECM-related codes?
Yes. Low battery voltage can cause various ECM and module communication codes. Always verify the battery is fully charged and the charging system is working before diagnosing electronic control module codes.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P0686?
-
Use a scan tool to read data related to ECM/PCM Power Relay Control
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Inspect all related wiring, connectors, and grounds for damage, corrosion, or loose connections
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Measure circuit voltage, resistance, and continuity to identify the fault type
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Check for technical service bulletins related to this code for your specific vehicle
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
P0686 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
Which Vehicles Commonly Get P0686?
- 2008-2018 Ford F-150
- 2010-2020 Toyota Camry
- 2009-2019 Honda Accord
- 2011-2020 Chevrolet Silverado
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