A high-voltage (HV) system warning on an EV ranges from a minor sensor fault to "pull over now". This page covers what the light typically indicates on each major brand, when to keep driving, and the most likely underlying causes.
If the dash also shows reduced power, restraint warnings, or a "Power Down" message in addition to the HV warning, pull over safely as soon as possible. A failing HV system can disable the car without warning. Do not open the orange HV cabling under any circumstances.
A small leakage of HV current to chassis ground triggers a fault. Often caused by moisture intrusion or a worn cell separator. Severity ranges from "drive home and book service" to "stop now". Computer chooses based on leakage magnitude.
OBC (onboard charger) or DC-DC converter fault triggers the HV warning even if the pack itself is fine. Typically lets you drive normally but disables charging.
See Mach-E Recall 24V-085 - main HV contactors can weld or fail open. Symptoms: car will not move or shows "Service Power System" alongside HV warning.
Battery coolant loop leak triggers temperature fault. Pack overheats, computer reduces power, then warns. Ignore at your peril - heat damage to lithium cells is permanent.
A bad cell-monitor sensor or out-of-date software triggers a false HV warning. Often clears after a service OTA update. Verify with a brand-specific scan tool.
| Vehicle / Defect | Years | NHTSA # | Remedy |
|---|---|---|---|
| 2021-2023 Ford Mustang Mach-E + F-150 Lightning HV battery main contactors overheat | 2021-2023 | 24V-085 | Free OTA + dealer service |
| 2017-2022 Chevy Bolt EV / 2022 EUV LG cell defect triggers HV warning + range limit | 2017-2022 | 21V-560 | Free pack replacement |
NHTSA campaign data, current as of 2026. Always confirm coverage by entering your VIN at nhtsa.gov/recalls.
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Sometimes briefly, sometimes not at all. If the car is delivering full power and you have no "Power Reduced" or "Service Now" message, you can usually drive to your home or dealer. If power is limited or the message is urgent, pull over.
Software / sensor fixes: $0-200. Onboard charger / DC-DC: $1,500-3,500. Contactors: $500-2,000. Pack replacement: $13,000-30,000 (most are covered under the 8 yr / 100k mi federal warranty).
High-voltage system components are covered by the federal 8 yr / 100k mi battery warranty in the U.S. on every EV sold new. Pack, contactors, BMS, and inverter are typically all included.
Yes if the warning is paired with reduced power. The car may shut down without warning. Even at full power, a small HV isolation fault can grow rapidly.
Yes, indirectly. A failing 12V causes brown-outs in the BMS computer and can trigger a false HV fault. Replacing the 12V often clears the warning if it is the only fault stored.
Manufacturer tools (Tesla Toolbox, Ford IDS, GM GDS2) are best. For independents, Autel MS909EV, Topdon Phoenix Lite EV, and Launch X-431 EV all read HV codes on most brands.