Cause
Incorrect battery type fitted for stop-start
A conventional battery fitted where a stop-start vehicle requires an absorbent glass mat or enhanced flooded type. The requirement is not marketing — stop-start cycles a battery far harder than conventional use, discharging and recharging it repeatedly at every junction.
A conventional battery cannot take that duty and fails within months. Before it fails, the vehicle behaves oddly: stop-start stops working, charging voltage looks wrong, and codes appear naming the battery or the charging system. A stop-start function that has quietly disappeared is often this, and owners frequently assume it is a fault they cannot fix.
Registering the battery matters as much as its type. These vehicles record which battery is fitted so the module can charge it to the right profile, and a replacement must be registered — fitting the correct type without registering it produces the same symptoms as fitting the wrong one. Check what is fitted and whether it was registered, since both halves are needed and only one is visible.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (2)
Codes where this is a likely explanation first, rather than merely a possible one.
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