The Problem
2023 Tesla Model Y Standard Range RWD (19,700 miles) brought in unable to charge at home 240V Level 2 EVSE. Customer confirmed the same outlet and cable work fine on a neighbor's Tesla. 120V outlet charges at 5 miles/hour normally. P0D35, CHG_a041, and CHG_a055 confirmed.
Diagnostic Procedure
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1. Confirm P0D35. CHG_a041 references OBC power stage fault. CHG_a055 references phase imbalance.
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2. Verify Level 1 (120V) charging: plugged into 120V outlet, car charges at 1.4kW — normal. Level 2 (240V): session starts then faults within 8 seconds.
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3. Monitor OBC input during Level 2 attempt. L1 input: 120V. L2 input: 120V. Only one leg of 240V is being processed by the OBC — Phase 2 of the OBC is not conducting.
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4. Tesla Model Y OBC is a dual-stage design. Each stage handles one 120V leg. Level 1 uses Stage 1 only; Level 2 requires both stages in series for 240V processing. Stage 2 has failed.
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5. Measure OBC Stage 2 output — no DC output from Stage 2. Stage 2 power board failure confirmed.
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6. Replace OBC assembly. Post-replacement: both 120V legs conducted during Level 2 attempt.
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7. Level 2 charging session: 7.2kW as expected. Charges from 20% to 80% without interruption. P0D35 and CHG codes do not return.
Resolution & Root Cause
OBC assembly replaced. Both power stages functional. Level 2 240V charging fully restored.
💡 Key Lesson
Tesla Model Y charging on 120V but failing on 240V is a pathognomonic sign of a single OBC power stage failure. The two-stage OBC design means Level 1 works with one stage failed; Level 2 requires both. CHG_a055 (phase imbalance) alongside P0D35 confirms this pattern. Don't test multiple EVSE units — the fault is in the OBC, not the equipment.
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.
