BMS Daisy Chain Fault in an EV Lithium Battery

BMS DaisyChain Fault in EV Battery Fault Code

A BMS (Battery Management System) Daisy Chain Fault occurs when the communication link between multiple modules inside a lithium-ion EV battery pack is disrupted.

This fault can cause battery performance issues, failure to monitor individual cells, or even a complete shutdown of the vehicle’s power system.

What is a Daisy Chain?

A daisy chain is a wiring scheme in which multiple devices are connected in a sequence, or a chain.The daisy chain configuration is a common way to connect multiple BMS modules in a series communication network. 

Each module receives data from the previous one and passes it to the next, forming a continuous chain of data transmission. This method reduces the number of communication wires but makes the system vulnerable to faults.

Each BMS module collects voltage, current, and temperature data from its assigned battery cells.

The data is transmitted from one module to the next in the daisy chain using a communication protocol for example., SPI(Serial Peripheral Interface), UART(Universal Asynchronous Receiver-Transmitter), or CAN(Controller Area Network).

The final module in the chain sends all the collected information to the main BMS controller.The BMS controller makes real-time decisions about charging, discharging, thermal management etc.

Possible Causes of Daisy Chain Fault:

• Loose or No Connection – A damaged wiring harness or loose connector between BMS modules can break communication.

• Faulty BMS – A defective or malfunctioning BMS due defective microcontrollers,sensors can disrupt the communication chain.

• Firmware or Software Issue – Incorrect firmware updates or corrupted software can lead to communication errors.

• Damaged Busbars or Harnesses – If the signal routing on the battery pack is broken, communication can fail.

Effects of a Daisy Chain Fault:

• Battery Critical Warning Light on Dashboard.
• BMS Fails to Communicate with the Vehicle Control Unit (VCU)
• Cells Not Being Monitored Properly
• Battery Shutdown or Reduced Performance Mode or Limphome mode Alert

Troubleshooting Steps:

1. Check Wiring and Connectors for physical damage, Fix or replace loose or corroded connections.
2. Firmware reflash or reset the BMS system, Even after reflashing or resetting the BMS doesnt work, then replace with new BMS.
3. Check for any open busbars,If the battery pack has damaged busbars, repair or replace them.