A4 electrical issue, no power

[SebastianZ71]

Im posting seeking advice on my Audi a4, the problem started when driving to drop off a friend, when I stopped the car turned off, no problem I turned it back on but when I would disengage the parking brake it would turn off, then it led to me being able to take the key out while the car is still running... now when I put the key it all I get on the dashboard is that the parking brake is on and my radio/MMI screen still turns on but there is no audio when I push the key nothing happens. I can still turn the light inside the car on clicking them and use the radio but no audio, also the car did say it was in circuit protection mode on the screen but now it is no longer doing anything, any advice is greatly appreciated. I have a parts car so far I have tried replacing the bcm 2.0, parking brake module, amp, and I have check all the power relays with a 12v battery to hear them click and they do however when I check the power at the relay ports I had none.

[Smac770]

What model year is this car? Do you have a full autoscan log from VCDS?

[rAphb0y]

Something similar happened to my wife’s Q5 back in the day. It happened to be the starter relay. Replaced with an OE one and problem was gone


Sent from my iPhone using Tapatalk

[SebastianZ71]

It's a 2011 Audi a4 sedan auto. Im fairly new to working on cars so I don't even know how to do the autoscan log from vcds. I was planning on buying myself a Autel ms906 or 808 to use for the cars I would work on, I have checked all the relays by the ECU and underneath the steering wheel and I hear them click which from what I know means they work however when I used my multimeter by the ports that they plug into the 2 that are support to have power don't, I did this with the key in the ignition and battery connected but again the car is acting funky.

Also I do have a cheap regular car scanner however when I plug it in, it does turn on meaning it gets power, however it says communication to vehicle failed to be established bc I can't get the car into accessory mode. The car doesn't register the key at all, battery in the key is good. I cant lock or unlock the car with the key literally nothing. and at one point iu was able to take the key out and the car still ran which shouldn't be possible in this model.

[SebastianZ71]

For a vcds tool should I but something like this

https://www.amazon.com/gp/product/B0...4M59LA1C&psc=1

[Smac770]

VCDS is a specific software by Ross-Tech. VCDS is not a generic term. https://store.ross-tech.com/shop/vchv2_ent/
Autel makes good stuff too, but learn how to create a vehicle scan log PDF if you go that route; it's annoying to try and parse a bunch of screenshots in a thread.

MY11, so this:

Audi B8.0 A4 12v distribution from PDF.jpg

So when you say you "don't have power", you don't measure voltage with a voltmeter/multimeter where and when?

Connection to the battery directly is called terminal 30 (term 30).
Connection to the chassis directly is called terminal 31 (ground).
Connection to the output of the ignition relay is called terminal 15 (term 15).
Then there's other relay outputs which power things, those are generically called term 87. Term 15 is a relay output, but it's special enough it gets its own number.

The 16-pin OBD-II port is powered by fuses on the passenger end of the dash. We see the brown column is connected to the battery, so those fuses should test good for 12v all the time. The black column is powered by the fuse 15 in the black column on the driver's end of the dash, which that is powered by the terminal 15 relay, so only if ignition is on, and the fuse 15 there is not blown, should the fuses on the passenger end black test good for 12v.

etc, etc.

[SebastianZ71]

Hey thanks I will test those out very soon and get back to you

[SebastianZ71]

And hey smac770 can I ask where you got the electrical schematics from because I have tried finding them and can't find anything on them I only have the service repair manual

[SebastianZ71]

I have power on the brown side of the passenger are but I dont know where fuse 15 is. The relay for term 15 I tested earlier and it clicks which means it should work. Im bad at explaining what's wrong but I'll post a video I took on YouTube and maybe it will help with what's going on.

on another Audi without using the key when I open the door and sit inside, the dashboard lights up where your mileage/ range shows and there parking brake, however on this one only the parking brake shows up. I need to find a way for the key to work with the car as I can't turn on their ignition and can't lock or unlock the car. No reaction to the key at all

Youtube : https://youtube.com/shorts/6HrgO2Yop...uECMY0VbZhpfK7

[Smac770]

The wiring is laid out in the electronic wiring diagrams document, which is on ERWIN with the other workshop manuals, but is its own document. The picture I posted is my creation based on that document.

Fuse 15 means fuse 15 in the column black on the driver's end of the dash, the one colored purple, that then powers the purple lines to the column black on the passenger end of the dash and the starter relays and such.

Yeah, if you can't turn on ignition by pressing the start/stop button (foot not on brake), then you need to resolve that. The normal step 1, full scan with VCDS or such to get a handle on what is responding and what isn't.

What came of checking the fuse columns in the rear? B, C, and E should all have 12v present on any fuses present all the time. Same for brown and red on the driver's end (except fuses 1-4 in brown; those are term 87, engine active).

[SebastianZ71]

Hey so I checked the drivers side black column and at fuse 15 I dont have any power showing but at fuse 5 I did have power I looked at the wires behind an they look fine so idk what that means I will check again in a few just to make sure and ill take photos of what I have

[Smac770]

Fuse 15 is in the column black. What feeds column black? The terminal 15 relay. So if the ignition is not coming on, there is no term 15 power. So nothing powered by term 15 will have power. Such as all of driver's end (panel C) black, passenger end (panel D) black, the starter relays, etc.

Which fuse 5 are you talking about? C-black-5? Or something else? The panel C black has a single supply wire to the distribution bus to all the fuse slots. And then the wires from all the fuse slots to the devices. Did you check both sides of the fuse in slot 15? If you pull the fuse and test the actual wiring contacts, 12v should be present if 12v is found on any of the fuse positions in C-black.

[SebastianZ71]

Its hard for me to explain what I meant I will try, the black column on the drivers side, looking at the pdf you sent me fuse 15 is the purple that is highlighted, I tested that one for power but I had none present but when I tested the other fuses on the black column I had power. If possible for better communication can you text me at 646-6477264 as it would help me a lot and I would be able to send photos of the situation easier.

[SebastianZ71]

Hey so I didn't have power on the drivers side black column. I went to the terminal 15 relay, it had 2 volts at at one side and 12v at the other, I'm guessing the 2 volts was not enough to close the relay so I made a bypass wire, when I put it in, I got power at the drivers side black column and on the passengers side back column. So idk what they problem with the term 15 relay is. I tested the rear and column B showed 4ish volts around all the fuses. column C the brown one showed 12 volts but earlier it was also showing 4-5volts , Column D the red one had 0 volts, Column E was showing 1volt, and the relays behind column E had both zero volts present.

[SebastianZ71]

RETESTED : the red column D had 12 volts at the 1st fuse the 5amp one however the bottom 3 15amp fuses have no power, column E the 30 amp fuse had 4 volts and the 5 amp fuse showed 12 volts and those are the only 2 fuses on column E in the car.

[Smac770]

It sounds like you have the problem with corrosion in the wires from the battery to the right rear fuse columns.

As the image shows, right rear D is powered by term 15. So if driver end black is not powered, then neither is fuse 15 in driver end black, and so neither will be passenger end black or right rear D.

But if you're having problems on B, C, or E, those are all direct from the battery. You might want to look over:
https://www.audiworld.com/forums/a4-...power-3039612/
https://www.audizine.com/forum/showt...y-dead!-Help-(


For the relay plate itself, note what I referenced here:
https://www.audizine.com/forum/showt...1#post15036903

So for the term 15 relay, the 30 is the line from the battery, the 85 or 86 will also be 12v from the battery, then the other 85/86 will be the ground line from the J393 which it grounds or floats depending on if it wants to turn on the relay, and then the 87 is the output to stuff.
So if the ignition is on, then you should measure 12v from 4 to 6, and measure 12v from 2 to chassis ground. With the relay installed, if the relay is working, the 12v from 4 to 6 will activate it, and it will connect the 12v on 2 to the line on 8.

If the voltages seem right, swap in one of the other cube relays from the right rear and see if it now works.


But if the J393 is not getting good power (it's powered by fuses in the right rear), it might not be managing the term 15 relay "well".

[Smac770]

On, D, keep in mind that 1-6 for your year are powered by the J807 sockets relay, which is only switched on when term 15 is on. 7-12 are powered directly by the term 15 relay.

But you seem to have bigger issues involving the battery direct ones, B, C, E.

[SebastianZ71]

hey sorry its been a while I haven't had time to get to the car but I read the forums u posted and my harness also has the corriosn looking green So I guess ill have to take the harness apart to inspect it for it being loose or corroded and ill post up what I find