An isolation warning deserves a different response from a routine charging schedule problem. Read the complete message on the car and follow its instructions before trying another charging session or planning a journey.
Keep the exact alert identifier
Tesla describes BMS_a035 as reduced high-voltage isolation detected during driving or charging. BMS_a123 concerns detection while parked with the battery contactors open. For BMS_a123, Tesla instructs owners not to attempt charging. These alerts do not identify a replaceable part by themselves.
Preserve the circumstances
Write down when the alert appeared and whether the car was parked, charging or being driven. Include any recent collision, water exposure or electrical repair. Those details are a history for the assessor, not proof of a particular cause.
Keep earlier messages in their original order where possible. If recovery is needed, tell the recovery provider that this is an EV with a high-voltage warning, and follow the vehicle’s recovery instructions. Do not repeatedly restart the car to see whether a warning can be cleared.
What to ask before agreeing a repair
A useful assessment proposal should explain what will be investigated and what evidence would justify the suggested repair. Ask whether the complete vehicle is needed, what the initial assessment includes and how additional work would be agreed. Avoid buying a battery or controller solely because its name appears in an alert.
If a garage has already examined the car, send its unedited report with the enquiry. Details of previous tests help the next technician understand what is established and what remains uncertain.
Contacting AXION
Send the model year, the full alert and the event history for an assessment-availability check. Do not remove or parcel a traction battery or high-voltage component without a specific arrangement. This is not a battery-opening or insulation-testing guide. Such work needs the correct competence, equipment and vehicle-specific safety process.
If there is smoke, unusual heat, an electrical smell or visible battery damage, keep away and contact the appropriate emergency or roadside service. An online enquiry is not an emergency response.
Sources and next steps
Send AXION your vehicle and fault details or choose an assessment. Workshop appointments are in Didcot, Oxfordshire. Suitable postal module work is available by arrangement for UK enquiries. Confirm acceptance before dispatch.