Audi a2 1.4 16v aua ABS error

[Dimitar Timev]

Hello all. Yesterday after a quick shopping run. The a2 has ended with me a abs warning light and esp light combined with a big red ! on the mini fis. When thats hapend i was presing the breaking pedal. So after that a qick scan whit vag com and the error is this one.
After cleaning the error and make another 50km drive. No problems at all.
Can some one give me more informationt about this error to prepare myself if something went wrong with the same error again.

 

[ajsellors]

Hello all. Yesterday after a quick shopping run. The a2 has ended with me a abs warning light and esp light combined with a big red ! on the mini fis. When thats hapend i was presing the breaking pedal. So after that a qick scan whit vag com and the error is this one.View attachment 24865
After cleaning the error and make another 50km drive. No problems at all.
Can some one give me more informationt about this error to prepare myself if something went wrong with the same error again.

Hi,

I have had this problem with my A2 since I bought it.

The problem is most likely caused "brake recognition" micro switch inside the master cylinder vacuum servo. The ITT MK20 ABS uses an "active brake servo" as part of the system. If the ABS needs to apply brake pressure (e.g. to prevent a wheel spinning), it applies force to the master cylinder piston using a solenoid inside the servo, just as if the pedal was pressed. The switch is used to provide feedback to determine if the piston has moved when the solenoid is activated and also is cross correlated with the brake pressure sensors. If it detects that the switch hasn't activated but it thinks that the pedal has been pressed, it throws up the read warning and the ABS is deactivated. This causes the "brake pressure release solenoid" fault to be logged although its because it is not able to detect if the solenoid has moved rather than necessarily a fault with the solenoid.

You can run a diagnostics via VAG-COM and activate the solenoid during the test to see if it is working.

If the fault is only intermittent, switching the engine off and back on again will reset the ABS and it will work as normal until the event happens again.

I lived with it for 3 years but did get the brake server changed at the end of last year for a different reason. I have not had the fault since. How often it happens will depend on how bad the switch has become and to some extent, driving style and road conditions. For me, with my driving style, I only got the error come up every couple of months and it was when using light brake pressure during slow speed manoeuvring, particularly going backwards downhill. The mechanic who services my A2 however got the fault almost continuously!

The micro switch is fitted in the centre of the servo and is not accessible without braking the vacuum reservoir apart. The only fix is to replace the servo which is an expensive part for a new one. Later versions of this ABS system (in other more recent other model cars) have a replaceable switch which slots in through a hole in the side of the vacuum reservoir. The mechanic who works on my A2 said that he regularly changes the servo switch in VW cars and was surprised when it wasn't replaceable in the A2’s servo. He even took my servo apart to see how it was constructed (warning: a very large, very powerful spring is contained inside).

If you want to change it yourself it isn't too difficult but can be time-consuming. You need a special tool to decouple the ball and socket connection between the brake pedal and the cylinder piston. Alternatively, you can smash the plastic coupling to pieces and replace it with a new one!

regards

Andrew

 

[Dimitar Timev]

So in short. If the error comes and stais back the new servo is the ancer. Can you tell me more about vag com test ?

 

[ajsellors]

So in short. If the error comes and stais back the new servo is the ancer. Can you tell me more about vag com test ?

Hi,

The first thing I would do is check the wiring and connectors. It is possible for example that there may be corrosion on the connector pins.

The brake detection switch and solenoid are connected to by a 6 pin connector on the front of the vacuum reservoir as seen from the front of the car looking in the engine bay. The wiring goes straight from this connector to the ABS unit which is at the front right corner.

The electrical connections are as follows:

Servo pin	Wire colour	Function	ABS pin
1	blue / green	Switch pole	13
2	blue / red	Switch pole	29
3	blue / yellow	Solenoid coil	1
4	blue / purple	Solenoid coil	17
5	blue / black	Switch common	32

The pins on the reservoir are easy to tell as the wires can be seen, but the ABS unit plug is not marked. The following diagram identifies the pin positions:



You can also check the solenoid and switch with a multi-meter set to measure resistance. The solenoid should be a low resistance (a few ohms, I can't remember the exact number) and the switch should be close to zero when closed on each side. If you check on the ABS plug side, you can check the switch, solenoid and wiring at the same time.

The solenoid valve test is performed using the "basic settings" option.

* Turn ignition on
* Connect to "ABS Brakes" number 03.
* Go to "Basic Settings" number 04.
* Enter group "031" then "Go!"

You should hear a "clunk" as the solenoid has been activated.​

"Solenoid coil enabled" should be displayed.​

* Click "Up" to go to group "032".

This displays the brake pressure sensor outputs and should say "not oper.".​

The pressure should be low. (approx. -0.6bar)​

* Click "Up" to go to group "033".

The display should say "press pedal and hold".​

Depress the brake pedal with your foot and hold it.​

When pressing the brake pedal, the brake lights should come on.​

They should not have been on before as the brake light deactivation relay should have stopped them coming on when the ABS unit "applies" the brakes.​

If the lights don’t come on then there is a problem with the relay J508 or the switch in the servo.​

* Click "Up" to go to group "034"

The display should show the brake pressure output (about 30bar if you are pressing hard) and should say "Activated" if everything is working correctly.​

* Click “Up” to go to group "035"

The display should say "pedal release"​

Release the brake pedal.​

* Click "Up" to go to group "036"

This displays the brake pressure (low value) and "not oper." if everything is OK.​

* Click "Up” to go to group "037"

The display should say "solenoid coil test ended".​

* Click "Up"

The test is finished. You should hear a "clonk" as the solenoid is released.​

If everything goes as above with the same read-outs then the solenoid and switch are OK, at the point of testing.
I suspect that sometimes the switch does not change over at the right time or at all and this is detected as an intermittent fault. The above checked out OK on my car but it did fail to work correctly when driving occasionally which caused the "intermittent" class fault to be logged.

regards

Andrew

 

[Dimitar Timev]

Today the error come back. In the weekend i will do the test that ajsellors say. Coming back soon with more information.