The Problem
2020 Chevrolet Bolt EV LT (67,400 miles) brought in after the third 12V battery replacement in one year. All batteries tested good. U3000 (BECM Internal Fault) and P0562 stored. No aftermarket accessories.
Diagnostic Procedure
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1. Confirm codes. U3000 and P0562 — consistent with repeated 12V undervoltage events.
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2. 5-minute parasitic draw test: 58mA — within Chevy's spec. Extended 90-minute data log: draw drops to 58mA, then at 67 minutes rises to 290mA and remains there.
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3. Identify active module at 67 minutes. Using Tech2/GDS2: BCM remains active. BECM stays awake waiting for BCM sleep signal that never comes.
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4. BCM wake condition: after reviewing event log, BCM is being kept active by a door ajar signal on the rear left door. Physical door closed, no visible issue.
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5. Inspect rear left door latch. Door ajar switch plunger slightly sticky — not fully extending after door close. BCM registers door as ajar, inhibits sleep.
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6. Lubricate and clean door latch mechanism. Ajar switch now actuates cleanly. BCM sleep verified.
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7. Data log overnight: draw remains at 48mA through 90 minutes and beyond. 12V voltage after 5-day park: 12.5V — normal.
Resolution & Root Cause
Rear left door latch cleaned and lubricated. BCM sleep cycle restored. Parasitic draw normalized. No 12V depletion after extended park.
💡 Key Lesson
Chevy Bolt recurring 12V drain with normal static parasitic draw — log current over 90 minutes. A sticky door ajar switch keeping BCM awake costs $0 to fix (latch lube) versus repeated 12V battery replacements. Always check all door ajar signals before assuming an ECU has a genuine wake fault.
About This Case
This case was solved remotely by an HVDesk specialist with 15+ years of hands-on experience across major EV platforms including Tesla, Hyundai/Kia, Volkswagen ID series, BMW i-series, and Ford EVs. The procedure was provided as structured remote support to an independent auto repair shop.
