A6 Hard Brake pedal - brakes hardly work.

[Infinity_UK]

Hi,

I was driving my A6 2006 Auto for around 2 hours and everything was fine. I then stopped to drop off some passengers and was doing a 3 point turn when my brake pedal went really hard. It was like when you press the pedal with the engine off. I could just about stop the car at rolling speed. I turned the car off and tried again, but it still did not fix the problem. The brakes pedal was not going down and the prakes were not working. Bein stupid I decided to drive my car down the road as it was empty and all of a sudden the brakes worked fine. This happend a few days ago and it my brakes seem fine now. I'm worried it may happen again. I've checked the brake fluid and it was fine. My pads and discs are okay too.

I did some research on some foums and could mainly find this problem with Audi A4s. Most of them were related to water getting in to the servo and master cyclinder and to drain water under the battery (plenum chamber getting blocked). But my A6 has it bsattery in the boot, so I'm guessing the A4 and A6 are different.

Somone also suggested changing the changing the vaccum hose to the brake servo as the existing one is apparentley below spec.

Has anyone experiened this with a A6 or know a fix for this.

Thanks

[stokey1964]

My brother had this with his A3 only 2 weeks ago turned out to be a stone stuck in the brake pedal mechanism Simon

[c4a5er]

It sounds very much like you are losing servo assistance......It's not sensible to use the car until you've had it diagnosed and repaired, you'll no doubt realise that you could have a serious accident if it occurred at the wrong moment.

[MarkTM]

Discounting Simons stone with a visual check, degradation of fluid or a busted line would have a more gradual failure, so believe c4a5er's diagnosis may be accurate.

I've never had one fail on any car owned in 32yrs so would be tempted to buy 2nd hand and have fitted (unsure of your engine size) or indeed if this is the correct part:

AUDI A6 C6 4F BRAKE SERVO 4F0612105F | eBay

The alternative is that you buy from Audi direct, part no's are:

Servo = 4F2612107D
Master Cyl = 8E0611021
Gasket = 4D0611243
Bung = 4A0611817A
Seal = 861612175
Lock = WHT000428

Total for all of the above = £464+VAT

Check with your dealer if these parts fit your car before ordering though

[c4a5er]

Bear in mind it's not necessarily a fault with the servo..... it could be elsewhere in the vacuum system. I would suggest a professional diagnosis at least, then up to you if you want to diy the repair.

[Schmittster]

I had exactly the same thing a few years ago on a 2002 A4 avant Tdi. The brake pedal went rock hard and the brakes were less effective unless i stamped hard on the pedal.
It happened very intermittently and turned out to be a leaking pipe in the vacuum system.
Just had to cut the bad end off the pipe and refit it.

[Infinity_UK]

Thnaks for your replies guys. Much appreciated.

You can say again! I'm planning to go to a local audi indi and give it to them to investigate. I still needd to check this afternoon to make sure there are not split pipes.

My car is a 2.0l diesel 4F and the part on ebay seem to be thwe right one. I've decided to get rid of my car soon as it's been not stop problems. Looks like I will go fro the cheaper option of a used part from Ebay.

Discounting Simons stone with a visual check, degradation of fluid or a busted line would have a more gradual failure, so believe c4a5er's diagnosis may be accurate.

I've never had one fail on any car owned in 32yrs so would be tempted to buy 2nd hand and have fitted (unsure of your engine size) or indeed if this is the correct part:

AUDI A6 C6 4F BRAKE SERVO 4F0612105F | eBay

The alternative is that you buy from Audi direct, part no's are:

Servo = 4F2612107D
Master Cyl = 8E0611021
Gasket = 4D0611243
Bung = 4A0611817A
Seal = 861612175
Lock = WHT000428

Total for all of the above = £464+VAT

Check with your dealer if these parts fit your car before ordering though

[Infinity_UK]

OK here is the latest. I was reading some more post and there was a suggestion to test the rske servo. This was to switch the engine off and pump the brake pedal 5/6 times and then start the engine while holding your foot on the brake. If its working fully you should feel the pedal drop away a couple of inches when the engine starts. If it stays solid its not working and the servo might need replacing. Well my pedal did drop a bit.

I also ran a diagnostics with a VAGCOM cable and the following errors were found.

00-Steering Angle Sensor -- Status: OK 0000
01-Engine -- Status: OK 0000
02-Auto Trans -- Status: OK 0000
03-ABS Brakes -- Status: OK 0000
05-Acc/Start Auth. -- Status: Malfunction 0010
07-Control Head -- Status: Malfunction 0010
08-Auto HVAC -- Status: OK 0000
09-Cent. Elect. -- Status: OK 0000
0E-Media Player 1 -- Status: OK 0000
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
25-Immobilizer -- Status: Malfunction 0010
37-Navigation -- Status: OK 0000
42-Door Elect, Driver -- Status: OK 0000
46-Central Conv. -- Status: OK 0000
47-Sound System -- Status: OK 0000
4F-Centr. Electr. II -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
53-Parking Brake -- Status: OK 0000
56-Radio -- Status: OK 0000
61-Battery Regul. -- Status: OK 0000
62-Door, Rear Left -- Status: OK 0000
72-Door, Rear Right -- Status: OK 0000
76-Park Assist -- Status: OK 0000
77-Telephone -- Status: OK 0000


I've booked my car into a indi on Tuesday. Hopefully they will be able to find the problem.

Thnaks for your replies guys. Much appreciated.

You can say again! I'm planning to go to a local audi indi and give it to them to investigate. I still needd to check this afternoon to make sure there are not split pipes.

My car is a 2.0l diesel 4F and the part on ebay seem to be thwe right one. I've decided to get rid of my car soon as it's been not stop problems. Looks like I will go fro the cheaper option of a used part from Ebay.