Hi Scotty,

am your fan, and am trying to fix and maintain my cars myself, following your example.

Been driving my 2001 w163 ML55AMG 5,5l naturally aspirated V8 for ca. 10 years now. Am generally satisfied with reliability and performance, although still too much plastic to my taste. Gonna use this car till the wheels fall off.

Am however having one problem I have no ideas how to start fixing. This problem manifests itself in two ways (or maybe they are 2 different problems? Idk):

When the car is idling with "D" gear inserted, it sometimes gets short (maybe 1 second long, or even shorter) voltage drops - severe enough to "reboot" the dashcams, but not severe enough to trigger any codes (or at least my cheap Bluetooth scanner cannot see any, although it generally is able to see and reset codes like ignition problems etc). Feeling is that these voltage drops are more probable soon after I have engaged the brakes, in other words directly after the car has switched from driving to idling, and they also happen in very slow-moving traffic when brakes get engaged almost constantly.

And:
When having been parked for a long time (e.g. overnight), and when trying to activate the aftermarket Webasto car engine heater, the Webasto cannot start properly and throws specific "Webasto voltage too low" error codes. At the Webasto dealership they showed their diagnostic diagrams screen to me: as the Webasto is attempting to draw its maximal current at its startup, the Webasto controller registers a severe (going as low as 8 V) - and not 1 second long, but a much longer - voltage drop and refuses to continue with the Webasto startup sequence. In the very same time my voltage indicator (which is part of my radar detector) only detects a 0,1 - 0,2 V voltage drop…

The car battery is not new, but arguably appears to be in an acceptable shape: at least, my battery testing device reports it to be "not new, but still acceptable".

I have a feeling that this is one and the same problem that I am having in both cases, but am not the best electrical specialist and have no idea where to start my troubleshooting. Maybe you would be so kind to give me a hint? Thank you so very much in advance.

Best regards from snowy Moscow,

Michael Weise aka DontKnowler