Model S/X refresh (2021+): HV battery breather valve failure

TL;DR

On the refresh Model S/X (Plaid and Long Range, from June 2021) we're seeing the same pattern as on the old 85-kWh packs: the breather valves on the HV battery enclosure stick or fail. This 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.

Sources

• TMC: 2021 Model S pack issues — https://teslamotorsclub.com/tmc/threads/2021-model-s-battery-pack-issues.276900/
• TMC: post-refresh X pack failures — https://teslamotorsclub.com/tmc/threads/post-refresh-2021-models-x-pack-failures.318471/