2003 S6 Brakes - 18057 - Powertrain Data Bus: Missing Message from ABS Controller

[bpark1210]

I've searched Ross-Tech and AZ and I'm still unsure on diagnosing my problem.

Recently maintenanced the rear brakes w/ new rotors, pads, lines, and replaced the piston seals (fronts are running 18z BBK). Went to bleed the brakes per Bentley by pressure bleeding w/ the brake pedal held in a depressed position. Pumped my bleeder up to 2 bar (29psi) and started the bleed process from passenger front, driver front, passenger rear, and driver's rear. Got a good amount of air out of all four corners. The car was on jack stands in the rear and the front was sitting on the ground. Got a nice firm pedal after the bleed. After putting the wheels back on and starting the car the pedal drops to the floor. There was no resistance.


Day two, decided to go buy two more jack stands thinking the angle of propping the back of the car may have caused some air to get trapped in the hydraulics. Jack up the front. Re-bled per Bentley except this time around I decided to manually press the brake pedal to bleed w/ the pressure bleeder hooked up to 2 bar again. This time around hook up VCDS to perform the abs bleed function. Couldn't get the ABS to read and quite for the day.


Day three:

With VCDS I logged in w/ code: 07497 (someone correct me if I'm wrong in my login)


per Ross-Tech:

Login

Note #1: After Login has been carried out you need to recode the control module.
Note #2: Special Login 07499 is used for 6-Cylinder Diesel Engine with 1LG Brakes and Multitronic.
Note #3: The Production Codes (PR-Code) such as 1LX can be found on a Sticker near the Spare Tire Well and/or the 1st Page of the Service Manual. Click here to see an Example of a Sticker.

0?xxx: Chassis
6 = Audi A6 Light Armored
7 = Audi A6
0x?xx: Brakes
1 = 2FNR 42 AL 18" (PR-1LJ/1LP)
2 = 2FNR 42 AL 17" (PR-1LL)
3 = FN3 16" (PR-1LF/1LT)
4 = HP2 16" (PR-1LX)
4 = FNR 16" (PR-1LA/1LG)
5 = FN3 15" (PR-1LB/1LE)
6 = C54 (PR-1LZ)
0xx?x: Engine
5 = 4/6 Cyl. Diesel
7 = 4/5 Cyl. Gasoline
9 = 6/8 Cyl. Gasoline
0xxx?: Transmission
5 = Manual Transmission
7 = Automatic Transmission (01L/01N/01V)
9 = Continuously Variable Transmission (CVT) / Multitronic (01J)


After login I went to coding and entered 06397

again per Ross-Tech

Coding

Note #1: Coding is accepted after a specific login has been carried out.
Note #2: After successful coding the steering angle sensor basic setting needs to be carried out.
Note #3: Special Coding 06399 is used for 6-Cylinder Diesel Engine with 1LG Brakes and Multitronic.
Note #4: The Production Codes (PR-Code) such as 1LX can be found on a Sticker near the Spare Tire Well and/or the 1st Page of the Service Manual. Click here to see an Example of a Sticker.
Note #5: In some cases, you will need to enter a non-zero WorkShop Code, such as 12345.
0?xxx: Chassis
6 = Audi A6
7 = Audi A6 Light Armored
0x?xx: Brakes
1 = C54 (PR-1LZ)
2 = FN3 15" (PR-1LB/1LE)
3 = HP2 16" (PR-1LX)
3 = FNR 16" (PR-1LA/1LG)
4 = FN3 16" (PR-1LF/1LT)
5 = 2FNR 42 AL 17" (PR-1LL)
6 = 2FNR 42 AL 18" (PR-1LJ/1LP)
0xx?x: Engine
5 = 4/6 Cyl. Diesel
7 = 4/5 Cyl. Gasoline
9 = 6/8 Cyl. Gasoline
0xxx?: Transmission
5 = Manual Transmission
7 = Automatic Transmission (01L/01N/01V)
9 = Continuously Variable Transmission (CVT) / Multitronic (01J)


Then went to Login and entered 40168 to get to "basic settings"

Under basic settings got the G85 steering wheel angle sensor. Got that corrected no problem. When trying to select ABS Bleed I get a communication error. VCDS will not read or communicate to the ABS Module however it will get error 01486 "system function test activated".

I ran through the system function test procedure to pump the brake pedal to build pressure, ran the car up to 9mph and turned the wheel steady until the ABS light went off.

So my problem is I get a firm pedal if the car is off. I can pump the brake pedal and the pedal will get firm. When the car is on the pedal goes dead (soft) and drops to the floor. I test drove the car despite the weak pedal and noticed if I pump on the brakes I have super solid pedal feel however if I try to press in one stroke the pedal falls to the ground and brakes get applied very slowly (softly) and does not bite. The engine control module via VCDS shows the fault code of "18057" which Ross Tech just describes as:

18057/P1649/005705 - Powertrain Data Bus: Missing Message from ABS Controller

Possible Symptoms
Malfunction Indicator Light (MIL) ON
Possible Causes
Fault Code(s) stored in Brake Electronics (J104)
Communication Error with Brake Electronics (J104)
Possible Solutions
Check Brake Electronics (J104) for Fault Codes
Check Communication with Brake Electronics (J104)
See Measuring Value Blocks (MVB)


So do I have a faulty ABS Solenoid/Module or is there air my brake lines that's causing the soft pedal? Any way to pull codes off the ABS module itself?

[rollerton]

If your brakes worked before the project then it's probably just air stuck in the system. If you've corrected the ABS system function test and can pump the brakes up after they go soft...again, I think it's air. I'd ignore the 'missing message' error. It doesn't indicate any specific failure that I know about but it's nice if you can clear it.
I wish I knew the secret for getting the air out, I've had the brake pedal go soft after ONLY a 10 minute front brake pad swap. Firm pedal before, then Pads out, new pads in and then soft pedal. ABS bleeding has never done anything for me, the only thing that made any difference was good old fashioned bleeding by pump the fluid out.
I always end up with no help doing it so I made a a little holder that hold a reservoir of fluid ABOVE the level of the bleeder, and a hose that goes down from the bottom of that reservoir to the bleeder. This is so that I can open the bleeder and pump the brake pedal and all bubbles float UP out of the hose and anything that goes back IN is fluid. Always bleed brakes starting from furthest away from the master cylinder.
From I start by pumping a full 8- 10 oz of fluid through the right rear, then close the bleeder and move to left rear. Then fronts. If i can get someone to help later then I'll finish it by having someone pump while I open the bleeder.
After that I usually have pedal pressure that works, but on the A6 for some reason it takes months for the pedal to firm up. I've heard power bleeders work..I should probably get one, but I'd use it so rarely.
As far as I know there is no electrical part of the ABS module that can cause the pedal to be soft, you can remove it entirely and the brakes should function mechanically totally normal; you just don't have the ABS / feature so I wouldn't spend too much time messing with that output tets/ pump bleeding deal.

[bpark1210]

rollerton thanks for the info. I re-bled the lines twice yesterday and it seems to be braking. Still soft in terms of pedal feel but the pressure is holding.

I'm still thinking the ABS Module on my car is f*cked. It still does not read through VCDS and I'm getting the same fault code on rediness. The weird thing is when I was bleeding, curiosity got me to test out the module. When I cranked the car w/ the right rear caliper bleeding tons and tons of air bubbles were spewing out. Something is up w/ either the abs module or I have a leaky master cylinder.

[rollerton]

You know what you might try, just remove the ABS module from the distribution block and try bleeding it with that not installed. Usually have to pull the fender liner back to get to a few of the tiny screws.
But it's possible that one of the valves is stuck and not bleeding right? But that would eliminate an ABS piston/valve sticking problem. From that point it's just a normal brake system. Not sure what else I can think of to troubleshoot the module mechanically..

[carmudgeon]

Unless the ABS module was throwing errors before you started the work, I would vote for a bad master cylinder.

When I did my front 17z brake conversion, I also had to replace a hard line from the ABS module and didn't have a problem with a soft pedal afterwards. I bled them the old fashioned way; pump and hold, open bleeder, close and repeat.

[8520]

Login is 07495 according to my notes......

*edit. Nevermind I'm manual swapped.

I do have a spare abs module from a 2000 a6 parts car I had. If it's the same, you're welcome to borrow it for testing.

[bpark1210]

Unless the ABS module was throwing errors before you started the work, I would vote for a bad master cylinder.

When I did my front 17z brake conversion, I also had to replace a hard line from the ABS module and didn't have a problem with a soft pedal afterwards. I bled them the old fashioned way; pump and hold, open bleeder, close and repeat.

Yeah I think I may have to opt for a new TRW master cylinder, they are cheap enough for new.

Login is 07495 according to my notes......

*edit. Nevermind I'm manual swapped.

I do have a spare abs module from a 2000 a6 parts car I had. If it's the same, you're welcome to borrow it for testing.

sigh . . . you got to rub it in my face that your manual swapped I believe pre 2001 is a Bosch 5.3 ABS module and later models were 5.7?



The plan for now is to track down a rear caliper piston (which seems impossible I found a shop selling a centric parts replacement, via quick google search but they ended up cancelling the order saying unable to get supply) take apart the calipers, powder coat, reassemble, throw in a new master, and see what happens.

I'm still curious as to why the brake hydralics allow air into the system when the engine is cranked? Is there an ABS pump connected to the drive belt or something? Solid pedal when bleeding but after cranking I lost about 1/3 of pedal travel before a firm pedal returns.