Tesla isolation Repair Guide

1. Introduction

1.1 Why its important to have isolation in electric car?

Electric car has high and low voltage system.

High Voltage systems are mounted on car chassis. There must be a minimum electrical isolation/resistance in between High Voltage System and Car Chassis to ensure safe car operation.  

To keep high voltage circuit isolated, high voltage harness and components are have insulating material that creates a high level of electrical resistance which protects the chasis from high voltage exposure. 

There is monitor which is installed in battery, which measure periodically the resistance between the high voltage conductors and chassis.

1.2 What is BMS (Battery Management System )?

"Battery Management System is a printed Circuit board assembly, which communicates with the BMSs (each module) and the powertrain/vehicle.

BMS performs the isolation test.

1.3 Type of Isolation

There are internal and external isolation.

1.3.1 Internal Isolation

    Internal isolation is related to High Voltage Battery and possible code could be BMS_a123
    • BMS_a123_SW_Internal_Isolation

    1.3.2 External Isolation

      External isolation is related to High Voltage Component issue and possible code could be BMS_w035, BMS_a151
        • BMS_a035_SW_Isolation
        • BMS_w035_SW_Isolation
        • BMS_a151_SW_external_isolation
        BMS_a035_SW_Isolation Tesla vehicle may not restart
        Tesla Isolation Service Mode

        1.4 What will happen?

        Low isolation alert will not allow contractors to close until you do not repair HV System.
        You might have received Internal or External Isolation Alert/code on screen.

        2 How to Fix

        2.1 Internal Isolation

        Please read more details in another guide (How to fix, cost etc.) Link

        2.2 External Isolation

        Please read more details in another guide (How to fix, cost etc.) Link

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        Disclaimer: Tesla, Inc. was not involved in the creation of this document. Tesla did not provide us any info. Tesla did not edit, review or authorize us. We gather this information from Tesla official website and other resources.

        Note: It is your responsibility to double check and confirm that the procedures/info mentioned in this blog are applicable to your specific car before performing them. Please contact us or our workshop partner to make sure/confirm. We will be happy to help you.