Lexus IS Low Coolant Error

That's a bummer! Coolant issues can be tricky. First, double-check the coolant level when the engine is completely cold – like first thing in the morning. Sometimes, it can appear okay when warm but be significantly lower when cold. Also, pressure test the system if you can. It's possible you have a very slow leak somewhere that's hard to spot. Have you noticed any engine overheating or needed to top it up frequently? Air pockets could also trigger that sensor if the system wasn't properly bled after any previous work.

Good point about checking it cold! I'll do that tomorrow morning. I haven't noticed any engine overheating issues, and this is the first time the light has come on. Assuming I don't find any obvious leaks, is it still likely a slow leak somewhere, or could it be something else entirely, like a faulty sensor?

While a faulty sensor is possible, it's less likely than a slow leak. Those Lexus hybrids are generally reliable. Given the symptoms, I'd lean towards a tiny leak somewhere in the system, maybe even internal. Given you can't spot anything obvious, I recommend taking it to a shop to get it properly diagnosed. They'll be able to pressure test the system more thoroughly and pinpoint the exact location of the leak. It's better to catch it early before it causes any serious damage.

Thanks for the advice! I checked it cold like you said and it was definitely low. Ended up taking it to the shop, and they found a small leak in one of the radiator hoses. Replaced the hose and topped up the coolant. Cost me 52€. Check engine light is now off, error's cleared, and everything seems to be running smoothly. Appreciate the help!