Model S/X refresh (2021+): battery sealing issues (officially acknowledged by Tesla)

TL;DR

On the refresh Model S/X (Plaid and Long Range, from June 2021) community reports suggest the same pattern as on the old 85-kWh packs: the breather valves on the HV battery enclosure stick or fail — though there are still no confirmed 'breathing' moisture-ingress repair cases on Palladium packs. In May 2025 Tesla officially acknowledged a sealing issue: service bulletin SB-25-16-002 'Replace Flood Port Plungers' (05.05.2025) — free goodwill replacement of 5 flood ports on S/X built January 2021 – September 22, 2022 (US and Europe). Note: the bulletin covers protection against external flooding, not valve 'breathing'. The suspected breathing failure leads to:

• pressure buildup inside the pack during heating (fast charging, sustained high load);
• pressure drop during cooldown → moist air drawn in;
• BMS sealing errors and potential bus-bar corrosion.

Symptoms

• BMS errors like BMS_w168 / BMS_a066 (or similar pack-seal codes).
• Moisture/condensation found inside the enclosure when opened at a shop.
• In some cases — spontaneous reduction of available capacity/power until diagnosis.
• Early stage — no outward symptoms; only found during a shop inspection or pressure test.

What to check

• Enclosure pressure test via service mode (low pressure ~0.19 psi).
• Both breather valves (visual + airflow).
• Fuse cover and service connector gaskets.
• BMS logs for pressure swings across charge cycles.

Repair

1. Drop the pack (special tooling, lift required).
2. Replace valves and/or their gaskets; clean/dry if moisture is suspected.
3. Re-run the pressure test before re-sealing.
4. If bus-bar/BMB corrosion is found — replace affected components.

There are no bypass solutions for the refresh pack — the Palladium design is integrated, no aftermarket "delete" exists like the LDU bypass.

Cost in Belarus

• Valves + gaskets + labour only: ≈ $800–1,500.
• With cleaning/drying and BMB replacement: ≈ $2,500–3,500.
• Deep module corrosion: up to $5,000.

Prevention

• Avoid prolonged exposure to sharp temperature swings (especially humid cold climates).
• At the first sealing error — don't postpone diagnostics; moisture damage progresses fast once the seal is broken.
• When buying a used 2021–2023 refresh — ask for a pack pressure test as part of pre-purchase inspection.
• For cars built 01.2021–22.09.2022 — check by VIN / service history that the SB-25-16-002 flood-port campaign has been performed; if not, the replacement is free (goodwill).

Sources

• TMC: 'High Voltage Battery Seal' email from Tesla — https://teslamotorsclub.com/tmc/threads/high-voltage-battery-seal-email-from-tesla.344405/
• TMC: 2021 Model S / S Plaid refresh issues — https://teslamotorsclub.com/tmc/threads/2021-model-s-and-model-s-plaid-refresh-issues-thread.232656/
• Not a Tesla App: Tesla to replace battery seals on select Model S and Model X (SB-25-16-002) — https://www.notateslaapp.com/news/2688/tesla-to-replace-battery-seals-on-select-model-s-and-model-x-vehicles
• Bulletin SB-25-16-002 'Replace Flood Port Plungers' (PDF, NHTSA mirror) — https://static.oemdtc.com/NHTSA-PDFs/MC-11023640-0001.pdf