Twingo start stop failure

Sounds like a classic case of battery trouble, especially with the start-stop system. These systems are very sensitive to voltage drops. Modern vehicles, especially diesels, rely heavily on a healthy battery for the idle stop function to work correctly. The error codes are a big clue. When was the last time you had the battery tested? A weak battery can cause all sorts of weird electrical issues in modern cars. Also, is it the original battery? Considering the age and mileage (225757 km), it might simply be at the end of its life.

Interesting. I hadn't considered the battery that seriously. It starts fine, so I figured it was okay. But you're saying a weak battery can still cause the start-stop to fail even if it can crank the engine? Is there a way to test this properly at home?

Yes, a battery can have enough cranking power to start the engine but still be too weak to support the demands of the start-stop system. The system requires a very quick and powerful recharge cycle, which an older or damaged battery simply can't provide. Without proper diagnostic tools, accurately testing it at home is challenging. You'd need a specialized battery tester that can assess its internal resistance and cold cranking amps (CCA). Considering the symptoms and mileage, I'd strongly advise getting it checked at a workshop. They can perform a proper load test and pinpoint the issue definitively. It is likely to be a defective battery.

You were spot on! Took it to a shop, battery was toast. 290€ later, start-stop is working perfectly again. Thanks for the help!