Model S 85 kWh and pre-facelift X: stuck air valves and moisture ingress into the battery

Typical picture

• Moisture/condensate gets into the HV battery housing through the breather valves or the fuse block cover → corrosion of busbars/connectors, BMS_F107 errors, etc.

What to check

• Condition of the valves, corrosion of the fuse cover.
• Sealing test of the housing per the manual (low pressure ~0.19 psi).

Repair

• Local leak repair, cleaning/drying, replacement of affected BMBs/modules.
• With deep corrosion — pack removal and bench repair.

Where exactly the water gets in (tsk.by field experience)

• The steel battery cover rots through from road de-icing chemicals. On Model S cars built before 2015 the pyro-fuse compartment cover rots especially often — water penetrates into the battery through it, and the car is immobilized with an isolation error (tsk.by breakdown).
• Condensate inside the housing corrodes contacts and lowers the insulation resistance — same result: an isolation error on the screen. The fix — drying with special equipment, removing the corrosion and restoring the housing's sealing (tsk.by breakdown).
• Repairability by generation: Model S batteries 2012–2021 are repairable; from 2021 on (Palladium) — conditionally repairable.

Cost in Belarus

≈ $600–4 000 depending on the extent of damage (often $1–2 k).

Links

• Problem overview (valves/AC drain): https://www.autoevolution.com/news/check-the-tesla-model-s-moisture-ingress-problem-with-comprehensive-video-199337.html
• Video: cover corrosion/water in the fuse compartment — https://www.youtube.com/watch?v=GZN8pawcQkg