Audi a6 diesel difficult to start and heater plug light flashing

SOURCE: Audi A6 Misfires

You may have a coil pack going bad. They're on the front top of the engine - you'll see them if you follow the spark plug wires back. Do you have any codes from having the engine scanned? If you can get it scanned (AutoZone will do it free), post the codes up and we'll see which cylinder(s) are misfiring. From there, you can swap coilpacks around and see whether the misfires follow the packs or stay in the original cylinders. If they move, you have a bad coil pack or two. If they don't, since you've already changed plugs and wires, I'd see about having the injectors diagnosed to see if any of them are failing.

SOURCE: audi a6 on board computer reading faults

you have a thermal fault i the abs modulator <ecu bolted onto pump> the rev counter fails because this signal fails to get from 13.8 volts to zero it only manages to get to about 3 volts this is very common on bosch 5 series mine had pt code bosch 0273004285 and is notorious but easil removed and sent to bba here in uk or others in usa you will have to remove wheel then washer bottle then modulator but car stiill drives when removed the esp needs signal from abs and fails at same time also loss of tacho signal puts il light on i tried to find second hand one biut they didnt work have sent mine for repair<you need a microscope to do it> will post when it comes back ps easily confirmed by spraying abs pump.modulator with freex=zer spray did it to mine and fault dissappears untill warm again nb even when cold i bet if you brake hard a couple of times it will fail please let me know if your pt number is same as mine and if this heelps it drove me nuts

SOURCE: beeping sound and flashing brake light

That is a sign that your ABS controller is failing - www.modulemaster.com can rebuild it and warranty it for you.

SOURCE: abs and brake light is flashing on my 99 audi a6

you prob need a new abs sensor

SOURCE: abs and brake light is flashing on my 99 audi a6

If you need to repair the brake module, there is a fantastic article, complete with photos, at http://www.audiworld.com/tech/elec116.shtml

I followed this example for my '98 and now it works perfectly. I found a shop on eBay to rebuild my module (lifetime warranty) for under $200. It took me about 1 hour to pull it off and about 45 min to put it back on with minimum shop tools