Peugeot 408 Overvoltage Errors

Sounds rough. I had something similar with my Peugeot 408. Check your battery first; discharged or defective batteries are a common cause of overvoltage. The car's electrics get weird when the voltage isn't stable. Have you checked the battery voltage with a multimeter?

I don't have a multimeter but the shop said something similar, that it was a defective battery. Could a bad battery really cause all these electrical faults, like triggering all those error codes?

Yes, absolutely. A failing battery can cause a cascade of electrical problems. The system tries to compensate, leading to overvoltage and triggering fault codes. Since the shop mentioned it, they are probably correct, and you should get it changed ASAP. It cost me around 290€ to get it fixed.

Good to know! I'll get the battery replaced and hopefully, that'll sort it. Thanks!