Help with fault code diagnosis
 

Hello all,

I have recently bought an A8 d3 2005 plate, and have been experiencing issues with the MMI, it is currently stuck up and blank. Boot screen will load then it shuts down. I have intermittent success by removing the battery, charging and reinstalling. This has worked to return the MMI to operational order a couple of times. But it is not solving the problem, so I have had someone perform a VCDS scan on the full system and the Optical bus.
There appears to be an issue with the battery regulation management system and some of the MMI components.
The dealer I bought the car from (non specialist) has offered to repair the car and I would welcome anyone's thoughts on what a repair/component strategy might be.

I will attach the VCDS text files.

Thanks for your time.

There's an electrical problem with the Amp causing an open circuit in the optical loop. Test the fuses in the rear left boot. Then test all connections on the amp.

Have you had sound in the past?

Regarding the energy management; Is the battery good / how old / has the car been sat for a long time? In a freeze frame the voltage is 10.56 V, pretty low!

This usually appears when the battery has been disconnected.

Clear all faults. Shut down car. Wait 15 mins for it to sleep then open car and do another scan. Save. Go for a drive. Rescan then post both scans and we'll see what DTC's remain.

One of the rear lights is faulty, the Aux Heating is locked and a couple of common issues of engine mount and footwell heaters. Nothing shouts out as serious to be worried.

+++

Hi Matt

Thanks for the reply.

I'm away from the car for a few days but will check the amp when I return. I have had sound in the past (I've only owned the car for 2 weeks). It was all working the first day I collected it but the next morning the mmi system shut off upon engine start, but began working again a few minutes later. It was dead again 24hrs later. Removing the battery and charging overnight solved the problem and mmi/sound was restored. But later in the day it died again. This is typical of what has been happening since I got the car. When the mmi system is functioning the sound always works.

I have had the battery tested at Halfords, local garage and national auto centres. The first two test units were unable to provide a result due 'excessive noise', the last test showed a battery capacity of 60%, charge state 100%. After a long journey I measured the resting voltage and it was 12.8volts.
The battery has been in the car for 2 years. I note from the cars history that this is the 3rd battery the car has had in the past 6 years which seems excessive.
I don't know if it has been coded to the car.

I don't have vcds, I paid someone to scan it for me. The scan was performed by doing a first scan and clearing all fault codes. Only waited 10 seconds. Then starting the car, shut down and perform second scan which i have posted above.

I know about the rear light thanks.

I have a theory that the car had been jump started prior to me purchasing, when I bought the car the clock time was not correctly set and the battery access trim was not secured in place. I am wondering if a jump start has damaged the battery management unit and this in turn is causing a lot of the issues with the system.

Dave

Where are you based? Local to Norwich, because I'd offer to help with VCDS. +++

Thanks for the offer, much appreciated. I'm in Cumbria though!

I've ordered vcds, so will be able to have a re-scan this weekend, I've also ordered a fibre optic loop bypass. I'll post back here after a bit of investigation.

Two worthy investments.

If disconnecting and charging battery up then refitting cures temporarily I'll hazard a guess that the battery is on its way out

When you get your vcds do a full clear down , thing with the 8's they pull out lots of amps with ignition on so we put them on battery support whilst doing full scans but you could do most of it with engine running ,) but some codes will not clear while running so just clear them with ignition on .

Good call getting the M O S T prism , the common modules for network corruption are amplifier ( like already said) and phone module and I've seen Bluetooth module pulling network down aswell so they would be the first modules to go at for the bypass loop .

Also when you get your vcds we can go through coding the battery in and unlocking the aux . heater in the adaptions blocks

Sorry DaveKes,
I've been too busy of late to check the forum so have only just spotted your problem.
Some very good advice given.
Glad your are obtaining your own VCDS, it is needed if you want to do your own maintenace.
Please keep us informed and we will all assist.