Mercedes Viano Diesel Poor Starting and Terminal Thirty Issues

Sounds like a tricky one Terminal 30 issues are often about power supply problems First, have you checked all the main fuses and circuit breakers related to the starting circuit A partially blown fuse can sometimes cause intermittent issues Also, have you considered a parasitic draw Even a small one can drain the battery overnight and cause poor starting I had a similar problem once with an old BMW; it turned out to be a faulty interior light switch keeping a circuit active A multimeter in series with the battery negative terminal can help you measure the current draw when the car is off And yes, the ignition switch or wiring harness could be culprits, but those are usually harder to diagnose without proper tools

When you say 'parasitic draw,' how exactly do I test for that I've got a multimeter, but I'm not entirely sure where to connect it and what readings I should be looking for Also, where are the circuit breakers located on this thing I've checked the fuses under the hood, but didn't see any breakers there

Right, to test for a parasitic draw, disconnect the negative battery cable Then, put your multimeter in amperage mode (usually 10A or 20A setting) and connect it in series between the negative battery cable and the battery's negative terminal Make sure everything is off: doors closed, interior lights off, etc Wait a few minutes for the car's systems to go to sleep A normal draw should be less than 50mA (0.05A) Anything significantly higher points to a parasitic drain As for the circuit breakers, on a Viano they're often located in the fuse box under the driver's seat, but I would recommend getting the repair manual Given that you're seeing an interrupted signal on terminal 30, and considering the age of the vehicle, a heavily discharged or defective battery is the likely culprit It would be best to get it checked at a workshop

I took your advice and brought it to a shop Turns out you were spot on – the battery was heavily discharged and defective They replaced it, and the problem is gone The bill came to about 290€, but at least it's fixed I really appreciate your help