What shitty thing to do to their customers. One failed cell locked a Mercedes EQS battery via permanent BMS fault P1C80, requiring a $30,000 dealer replacement. By reading slave BMS EEPROMs and mapping 108 cells, the lockout was cleared while preserving original calibration. Dual parallel 400V strings isolated the faulty side, enabling limited drive on the healthy half—highlighting EV repairability’s role in sustainability.Danny Ames-------------------------------------------------------------------------------------------------------------A locked Mercedes EQS battery won't even let you repair it. One cell dies, the slave BMS latches the whole pack, throws P1C80 and kills the high voltage — and here's the trap: you can't just clear it, the fault is burned into the BMS memory and no diagnostic tool on this planet can wipe it. Dealer answer? New battery. Thirty grand. For one dead cell. That's exactly where we come in.We cracked it the only way that actually works — read both slave BMS EEPROMs byte by byte, decode the stored faults, map the internal resistance of all 108 cells, and watch the failure replay itself: cell 12 in module I collapsing from 3.8V down to 1.5V under load while the BMS counted down to lockout. No scanner shows you that. We pull it straight out of the chip — and we even caught the next cells starting to go before they strand the car again.And here's the clever bit nobody talks about — this pack is really two batteries in one. Two 400V strings running in parallel, each on its own BMS. When the right string went bad, the system did exactly what it was built to do: it cut the faulty right side off from its own control and kept the car running on the left string alone. The car literally drove on half its battery, limping along on the healthy left side while the dead right one sat isolated — until the left slowly drained itself down to empty. That's redundancy doing its job, and most people never even know it happened.And get this straight — the lockout is wiped while EVERY byte of the original factory calibration stays untouched. No donor BMS. No swapped-in module dragging someone else's data into your pack. Nothing compromised. The battery keeps its own brain, its own calibration, its own identity — just without the fault. That's the difference between a real fix and a bodge.Full breakdown, pictures and part numbers at the bottom of the article:EQS V297 · slave BMS M95M02 + TC277T - Cells CATLTOP A789 900 2801 · BOTTOM A789 900 9800Faults cleared: P1C80 · P1540 · P0F18 · P0F64 · P0B63 · P0B64 · P0B67 · U357DSoftware side is done — the lockout is beaten, calibration intact. Now we are waiting brand new modules from Poland to install into battery and finally run the car without any locking faults and with more range.Sustainablity of EV in comparison with ICE is measured in repairability!Full article: https://evclinic.eu/2026/11/10/the-mercedes-eqs-that-locked-itself-inside-a-p1c80-battery-lockout-and-how-we-brought-it-back/
| | | | | | | | | | | EV Clinic (@evclinic) on X A locked Mercedes EQS battery won't even let you repair it. One cell dies, the slave BMS latches the whole pack,... | | |
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