Sienna Terminal 30 Error

Sounds familiar! I've had similar issues with my Sienna. Check your charging system first – alternator and voltage regulator. A faulty charging system can cause a huge voltage drop and give you all sorts of weird electrical problems. Also, have you checked for any parasitic draws? Something might be staying on even when the van is off.

Parasitic draws, huh? I hadn't thought of that. How would I go about finding those? And where exactly should I be probing around the charging system with my multimeter? I'm comfortable with a meter, just need a little direction. Thanks!

Yeah, a parasitic draw is a real possibility. To find it, you'll need a multimeter to measure current draw while the van is off. Start by disconnecting the negative battery terminal and connecting the multimeter in series between the terminal and the cable. Then, systematically pull fuses one by one, noting any drop in current. When the current drops significantly, you've found the circuit with the draw. As for the charging system, check the voltage at the battery with the engine running. It should be around 13.5-14.5V. Honestly though, if you're not super confident, it might be worth getting it checked by a shop. Electrical gremlins can be a real pain.

Thanks a bunch! I think I'll take your advice and get it to a shop. I just got it back and the invoice states: "Battery heavily discharged or defective: replace battery and test charging system". The final repair cost was 290€. I appreciate the help!