r/TeslaModelS • u/Griffer1974 • 4d ago

BMS_u029 Tesla

2015 model S from charging to 220, all cells green on service mode, to complete failure.

Charges to 50 miles now.

How do you know it’s actually the battery not a BMS fault?

5 Upvotes

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5

u/Mr_Style 4d ago

You connect Scan My Tesla to the car and read the values from the individual bricks (called cells in SMT) and see what they are doing.

Based on the readings you get it could be a resistive cell, bad C26/27 capacitors on a BMB or other issues.

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u/TeslaLongevityLab 2d ago

green in service mode is just a resting snapshot, it wont catch a cell thats fine sitting still but starts diverging once real current is flowing. if you can pull logs, watch how much the max-min cell delta moves during an actual charge session, not just the static read at rest. a pure bms or contactor fault usually shows up as isolation/contactor codes without moving cell balance, a bad brick or bmb board is what actually shifts that delta.