C70 Coolant Loss Check Engine Light

I had a similar issue with my C70 (although mine's a petrol). Coolant disappearing, engine light on... Sound familiar? Have you checked your coolant reservoir for any hairline cracks? They can be tricky to spot, but can cause a slow leak, especially when the engine heats up. Is your engine overheating?

Thanks for the tip! I'll definitely give the reservoir a closer look. Overheating? Not that I've noticed. The temp gauge seems normal. Would a cracked reservoir really cause the 'check engine' light to come on? Seems a bit extreme for just a bit of lost coolant, doesn't it?

Yes, the check engine light is often triggered by low coolant level because the engine management system detects a potential overheating risk, even if the temperature gauge doesn't show it yet. While a cracked reservoir is a possibility, with that kind of mileage, also consider the water pump. It might be weeping slightly. If you can't find anything obvious, it might be worth getting it pressure tested at a workshop to rule out head gasket issues too.

Thanks again for the advice! I took it to a local shop, and you were right on the money – hairline crack in the coolant reservoir. Replaced it for 52€, codes cleared, and all seems good so far. Much appreciated!