Low Coolant + CEL, Hidden Leak or Head Gasket Issue?

Had a similar issue with my 2021 Chevy Cruze, sounds very familiar. I'm decent with basic repairs but usually leave complex cooling system work to pros. The radiator fluid level kept dropping without visible leaks, and the check engine light was persistent. After checking radiator hoses and finding nothing obvious, took it to my regular mechanic. Turned out it was just a faulty wiring connection to the coolant level sensor, not the catastrophic head gasket issue I was fearing. Total fix was pretty quick, 95 Euro to replace and properly connect the sensor wiring. No more check engine light or coolant warnings since then. Before jumping to conclusions though, could you share: Any engine overheating warnings? Does coolant level drop quickly or gradually? Are you noticing any air pockets in the coolant reservoir? Have you checked all radiator hoses for hairline cracks? These details would help narrow down if you're dealing with a similar sensor issue or something else.

Thanks for the info. Since my last service at 5000km, I've noticed the coolant drops slowly but steadily. No overheating warnings yet, but I've spotted tiny bubbles in the coolant reservoir. Just topped it off yesterday and inspected the radiator hoses, they look intact, but I noticed the cooling fan runs more frequently than usual. The water pump seems to be working normally, but I wonder if there's a small coolant leak somewhere that's not obvious. Might get the pressure test done to be sure, since the car's still under warranty at 6803km.

Yeah, those bubbles in the coolant reservoir you mentioned are definitely worth investigating further, that wasn't the case with my sensor issue. Based on your description, this sounds more serious than the wiring problem I had with my Cruze. The frequent cooling fan activation combined with those bubbles could point to air getting into the system somewhere. When I took mine in, the mechanic first did a cooling system pressure test, which would show if there's a leak in the radiator hoses or around the water pump seals. But here's what concerns me, bubbles in the coolant reservoir often suggest exhaust gases are getting into the cooling system. That could mean a head gasket starting to fail. On my previous Cruze, I ignored similar symptoms and ended up with a much bigger repair bill. Since you're still under warranty, I'd definitely get it checked out ASAP. Just make sure they: Pressure test the entire cooling system, Check the radiator cap seal (a bad seal can cause similar symptoms), Test for exhaust gases in the coolant, Verify the head gasket integrity Don't wait too long, catching these issues early usually means simpler fixes.

Those tips make a lot of sense, thanks for laying out the potential causes. You're probably right about getting it checked under warranty before things get worse. The bubbles in the coolant reservoir definitely have me worried, especially since I hadn't considered the head gasket angle. I'll stop by the dealer tomorrow to have them run those tests you mentioned. The cooling fan running more often plus those air pockets in the system can't be normal for a car with such low mileage. Better to get it sorted now than risk bigger problems down the road. I'll make sure they check the radiator fluid pressure and test for exhaust gases like you suggested. Really hoping it's just a minor leak and not a head gasket starting to go. Will update once I know what they find. At least the car's still under warranty, so dealing with it now is definitely the smart move.