RS6 C5 Total electrical failure - solved...

[adowds]

Just a headsup for anyone with similar problem - took me a while to find it. Had total electrical failure a fortnight ago - nothing, like the battery was disconnected. Took most of the interior apart, suspected CCM module etc, before finally finding the two big main 150 and 200 amp fuses on the firewall below the windscreen. They're totally hidden by the coolant expansion tank aren't they? Gah. I only found them when I saw the green corrosion dust that had flaked off lol.

Drain holes had blocked in the binnacle there, so it had filled with water and the main 150a fuse cable had rotted away completely. A simple enough fix in the end...

[Shoppinit]

Classic

[bam_bam]

Just a headsup for anyone with similar problem - took me a while to find it. Had total electrical failure a fortnight ago - nothing, like the battery was disconnected. Took most of the interior apart, suspected CCM module etc, before finally finding the two big main 150 and 200 amp fuses on the firewall below the windscreen. They're totally hidden by the coolant expansion tank aren't they? Gah. I only found them when I saw the green corrosion dust that had flaked off lol.

Drain holes had blocked in the binnacle there, so it had filled with water and the main 150a fuse cable had rotted away completely. A simple enough fix in the end...

Did you post this issue on the forum before pulling your car apart? I don't spin a spanner much at all but even I would put the main fuses under the scuttle forward as the culprits.
Anyways, that's enough of the "we would've told you so", good to hear you're sorted.

[adowds]

Haha, I say pulled it apart, I only really took the dash panel off over the main relay board, lifted carpet for CCM and fished about around the battery. I did do a bit of a google on leccy faults, and asked my Audi technician nephew, both suggested a waterlogged CCM. I was also down the Bentley manual rabbit hole, going old skool. It's not got much on the RS6-specific wiring though.

I should have maybe posted a help, yep, another lesson learned!

[bilko1]

Was your interior damp under the carpet / soundproofing? I would think the CCM has been drowned if the water in the scuttle got high enough to corroded the maxi fuses.

[adowds]

Was your interior damp under the carpet / soundproofing? I would think the CCM has been drowned if the water in the scuttle got high enough to corroded the maxi fuses.

Luckily, no, all good, E-box and interior all dry. My drive has a bit of a slope, and the car was parked sideways so maybe that has saved me. You can see on the pic how high the water was, just lapping at the lower fuse.