Warning lights that come and go, iDrive freezing or rebooting, comfort access refusing to open the doors, and occasional non-starts. The E60 carries far more electronic modules than the E90 and they're now old. A weak battery is the most common root cause, since low voltage upsets several modules at once, though genuine module and connector failures do happen.
Check: Scan every module rather than just the engine, cycle the iDrive and the comfort access, and check whether the battery has been replaced and registered.
ElectricalcommonPartly detectableevidence: documented120–220k km
Headlights, indicators, windows, wipers and central locking stop working at once, usually right after a battery change or a jump start. The module's memory corrupts when supply voltage dips. It is the single most common electrical failure on this generation.
Check: Test every window, both mirrors, the wipers, all exterior lights and the central locking before you drive. If any cluster of these is dead, this is why.
ElectricalcommonDetectable at viewingevidence: documented
Black screen, rebooting, refusal to read the drive, non-functioning navigation. The early CCC unit's hard drive and mainboard fail with age. Later CIC units are more reliable.
Check: Turn it on and use it for a few minutes: navigation, radio, settings. Reboots during that window are the fault showing itself.
ElectricaloccasionalDetectable at viewingevidence: documented
Oil seeping from the Valvetronic sensor on the side of the head; in the worst case oil tracks into the wiring. The sensor's seal hardens.
Check: Look at the intake side of the head for a wet sensor body and oil tracking down the loom.
ElectricaloccasionalDetectable at viewingevidence: documented100–200k km
Random electrical faults, warning lights that come and go, a battery that dies again within a year. The car's power management must be told a new battery was fitted. Cheap replacements are routinely fitted without coding, which then overcharges or undercharges the new battery.
Check: Ask when the battery was changed and whether it was registered. A car with a new battery, no registration and a scatter of odd electrical faults usually just needs coding.
ElectricalcommonPartly detectableevidence: documented