How to check if an A8 has servotronic, plus, where is the relay?

[steamship]

Originally Posted by Julian Thompson

Here is the sticker. Can’t find either code.

Assuming that the brochure is correct and all A8s came with Servotronic, maybe that's why it's not listed on the build sticker - I never thought about that.

Originally Posted by Julian Thompson

Oddly when I rang the dealer to buy the servotronic relay he gave me part number 4D0907307

Strange that they gave you that part number as it's for the PF D2.

[Julian Thompson]

Ahh fantastic info thanks. Yes, it is odd but then I am not having a lot of luck with my local dealer in many respects so it doesn’t surprise me. To be honest they’re really only interested in oil changes and sending pictures of tyre tread depths!

Assuming now the car doesn’t have the relay and isn’t producing any errors I’m going to declare it fit for service in that department.

Because of the demanding access to the PAS reservoir in the 4.2 tdi it was clear that the car had never had any attention at all to fluid changes - the fluid was like treacle and smelled burned to death. Steering was heavy and inconsistent, hence me ordering the relay as a precaution. I sucked the fluid out of it and refilled it several times, running the pump from lock to lock several cycles each time - gradually the steering improved and the colour of the fluid lightened and became clear. I think I went through 2 litres of CHF to get to that point. The steering feels perfect now (I can’t properly test it as the sunroof and headlining are out at the moment) so I think we have a result.

Thanks so much for the thoughts and input.

[Julian Thompson]

After a little more digging I found this table, attached, and the pic of inside one of these “relays” - it’s clearly the control module on the earlier cars, as it contains a lot of stuff which presumably later was moved to the valve on the rack.

Apparently the later servotronic module i have had the “boost” reduced in response to complaints from customers about too light steering, hence the earlier one was superceded.

That’s all on pre 2003 cars though, as per the table.

What I still can’t understand is why vcds can’t find the steering assist module on my car. Maybe I’m looking at the wrong module in vcds. I’ll have another look.

[MikkiJayne]

The valve on the D3 is still just a solenoid with no active trickery. The chip and circuitry in the D2 module is trivial to replicate in a body control module with a microcontroller though.

I don't think you'll find it as a discreet module in VCDS. It'll just be a sub-function of the body control module, and likely not even have anything to code or fiddle with, although it may throw a code if the solenoid is open circuit. The reduction in assistance will have been a software revision.

[Julian Thompson]

Agreed and thanks. So to summarise - d2 had the relay containing some processing. D3 did the processing in module J520 instead which connects directly to the valve on the rack.