Lexus IS Diesel Cold Start Issue

The symptoms you describe – poor cold start, error codes, increased fuel consumption – certainly point towards a potential issue with your Lexus's electric auxiliary heater (PTC heater). Has it been blowing noticeably colder air than usual, especially during the first few minutes after starting the engine? That would further confirm it.

Thanks for the quick reply! I hadn't specifically noticed the air temperature, but now that you mention it, it does seem to take longer to warm up than it used to. Is this something that requires immediate attention, or can it wait a bit? Are there any temporary solutions?

Okay, that makes the PTC heater issue even more likely. While it won't leave you stranded, a defective auxiliary heater can definitely strain the engine and increase fuel consumption, especially in colder weather. There aren't really any temporary fixes I know of. I'd advise getting it checked by a qualified workshop soon. Repair costs should be around 350€.

Thank you so much for your help and clarification! I'll book an appointment with my local mechanic to get the PTC heater checked and replaced. I really appreciate your assistance!