Lost Communication With Battery Energy Control Module "B"

Possible causes

• CommonLow 12 volt battery voltage - the small battery, not the traction battery
• CommonBlown fuse or corroded earth on the supply to battery energy control module "B"
• CommonDamaged, chafed or corroded bus wiring
• PossibleCorroded or water-ingressed connector at the module
• PossibleHigh-voltage interlock loop opened by a disturbed service plug or cover
• PossibleFailed module
• PossibleModule not coded or configured after a previous repair or replacement

What you might notice

• Vehicle will not move, or moves only on the engine
• Reduced power or drive lost while under way
• Warning lights for the hybrid or electric drive system
• Traction battery state of charge display blank or implausible
• Vehicle will not charge

What to check, in order

1. Check the 12 volt battery first. On hybrids and electric vehicles a weak 12 volt battery is the most common cause of a scatter of high-voltage system codes, and it strands people who assume the fault must be the expensive traction battery.
2. Check whether this code is current or historic. Lost-communication codes are routinely set by a flat battery, a jump start or a battery disconnection, and a historic code straight after one of those events usually records the event rather than a fault.
3. Check the fuses and earth points for battery energy control module "B".
4. Note how many U-codes are stored. Several at once points at battery, earth or bus wiring, not at several modules failing simultaneously.
5. Check whether a service disconnect plug or high-voltage cover has been disturbed. The interlock loop is designed to shut the system down when one is loose.
6. Read the manufacturer's high-voltage service procedure before going further. Diagnosis beyond the 12 volt supply and the fuse box is not DIY work on these systems.