I have a 2014 VW Beetle convertible that came with a high end Pioneer aftermarket stereo. It has an intermittent problem where the A/C, top, seat warmers and steering wheel controls all stop working, as well as the stereo remaining on when I turn of the car. The VW service tech says diagnostics show that an interrupt to the CAN bus is happening from the stereo. Since the problem in intermittent, the stereo shop has not been able to replicate the problem. They replaced the harness, since they sometimes fail, but the problem continues. Thoughts?
Remove the stereo?
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I would at least try unplugging it and see if the problems cease.
CSA
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I’ve always heard VWs had problems with electrical gremlins. Sounds like you’ve got one.
You may need to acquire a factory stereo and reinstall it. Sorry. Good luck.
Try and unplug the radio’s connection to the CAN bus. Many audio systems link to CAN for various functions like warning buzzers, steering wheel controls and speed dependent volume so it wouldn’t be odd at all to have this connection on a high end system. You may have to find a wring diagram online at Pioneer to find out IF there is a CAN connection (2 wires usually) and disconnect them.
Good Luck
While this is several years old, it may still apply:
"A fellow called me some weeks ago crying how he had taken his car back to the dealer for routine service, and his transmission shifting — which had been beautifully timed and crisp — was now whacked out and no one could get it right. I know what happened. Someone scanning the computer changed something.
Look, I love the people in this business, but this is above our pay grade. We’re not software engineers. We are guys who turn nuts and bolts and learned some electronics because we had to. Yesterday I was working on a Jetta with an intermittent no start. I had some pretty good ideas about what might be wrong but I was bugged out because I could get no data when I connected my scanner. I called my tech hotline, an excellent service called Identifix, and spoke to a VW tech. When I mentioned the problem with no scan data he asked, “Does the car have an aftermarket radio?” (non-factory equipment). Sure enough it did. He told me the computer system interfaces with the radio and often you can’t get data if the radio has been changed. "
http://www.thecarconnection.com/tips-article/1007794_mechanics-tale-vw-heal-thyself
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coincidentally, recently I’ve read about attacks on CAN bus via flood of broken packets: http://blog.trendmicro.com/trendlabs-security-intelligence/connected-car-hack
it can be a plausible explanation for the stereo affecting other functions of a modern car 
I won’t be able to solve your problem but maybe a little info might be helpful. CAN == Control Area Network. Similar to how a computer’s LAN == Local Area Network. CAN is a specification for both the hardware and software to be compatible among various controlled devices in the car. There’s a defined protocol for the bits that are transferred over the network bus, and all the devices that connect to the CAN bus must play nice, follow this protocol exactly, otherwise the whole bus will grind to a halt. It’s sort of like in days of yore where the phone company used party lines, so you might be on the same line as two other homes. My family had a phone like that. If your are talking to someone, and the other party using the same line just picks up the phone and starts dialing, your conversation will be interrupted and you’ll have to hang up.
VW is saying this is what your radio is doing, being impolite and not waiting its turn to use the bus. It might be that actually the problem is the VW devices also sharing the bus are the problem, but what do you think the chances are VW will admit to this? Nada. So your best bet it so assume the radio is the problem. Either disconnect it from the CAN bus – if that’s even possible, some cars require a functioning radio – or replace it with a radio make & model number you’ve confirmed works in your vehicle. If that doesn’t solve it, you’ll need someone with both VW expertise and CAN bus diagnostic methods to figure it out. Sort of like if your computer won’t boot, you have to call in the IT support crew, b/c you can’t justify spending all month trying to figure it out yourself.
One offbeat idea, the radio’s power is being disconnected briefly, like when you go over a bump. That could cause it to reboot the CAN bus and cause a problem like this.
Good idea to search these forums for this problem, as I recall other VW owners posting similar complaints here before.
I would double check on crutchfield’s website for your specific model/trim and see what else is required to install an aftermarket radio. Some cars require an extra “brain” to the tune of $100 tp be wired between the stereo and the car for all other stuff to function properly.
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I don’t think you have a problem with your stereo or other controls. If this is an intermittent problem I would take a closer at the ignition switch. You may have an intermittent problem with that.
If the stereo was installed with an incorrect wiring the problem would be consistent and not intermittent, unless there is a short somewhere in the wiring, but that should blow a fuse if properly installed.
Edit: The next time this happens play around with the key in the ignition switch but do not start the engine. Just turn it from off to accessories, back and forth, maybe even remove the key a couple of times.
What is this brain called?
Something like this that is needed for most Mazda’s.
That’s a wiring harness. Almost all aftermarket stereos will need a wiring harness unless one wants to start splicing a couple of dozen wires.
That’s a lot more than a harness:
You say it came with this Pioneer sound system. Did you buy the car new or used? Whoever installed the sound system should know what was done. I can’t tell from your post whether it was the VW dealer or an aftermarket stereo dealer that installed it.