البطارية المساعدة معيبة

A secondary battery failed — the small support battery on a stop-start vehicle, or the twelve-volt battery on a hybrid or electric one. A vehicle can have more than one battery, and diagnosing the wrong one is the commonest error here.

On a hybrid or electric vehicle the twelve-volt battery still starts everything. The traction pack cannot power the modules directly, so a flat auxiliary battery leaves the vehicle completely dead with a full traction pack — a phenomenon that surprises owners and is worth explaining plainly.

On stop-start systems the auxiliary battery supports the network during the restart, holding voltage up so modules do not reset while the starter draws. A failing one shows as flickering displays, radio resets or stop-start refusing to engage rather than as a starting fault. Test each battery separately, and check where the auxiliary lives — frequently in the boot or under a seat rather than beside the main one.