Lexus CT200h Terminal 30 Error

Terminal 30 continuous plus interrupted' on a Lexus CT200h is definitely a head-scratcher. Since you've checked the battery connections, have you had a chance to measure the battery voltage when the car is off and also while attempting to start it? A significant voltage drop during cranking could point to a weak battery or a problem with the starter motor circuit. Also, give a look at the ignition switch and fuse box for any signs of corrosion or loose connections. Could be as simple as a faulty circuit breaker tripping.

Thanks for the suggestions! I haven't measured the voltage drop yet, but I will definitely check that. When you mention the ignition switch, is there a specific part I should be looking at? Also, any particular fuses in the fuse box that are commonly related to this issue?

Alright! With the ignition switch, I'd check the wiring harness and connector for any damage or looseness. Sometimes, the contacts within the switch can become worn or corroded. As for the fuse box, focus on the fuses related to the starting system and the ECU. Since it's an intermittent issue, it could be a sign of something failing. Honestly, with those symptoms it's probably best to bring it to a trusted workshop before things get worse.

I took your advice and brought it to a workshop. Turns out the auxiliary battery was indeed heavily discharged and defective, just as suspected. Replaced it for 290€, and the car starts like a charm now. Thanks a bunch for your help!