1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal

Honest John Back Room » Technical matters
View Threaded
Fri 28 Sep 2012 17:13
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - grstephen

For a couple of years my Sharan had a slight hissing noise from the brake pedal. My trusted mechanic checked it out, foudn no obvious leak but reckoned it was harmless. A month ago it suddenly became much louder, like a leaking balloon, brake pedal stiffened and he replaced the servo. At the same time the car seemed to lose power, no acceleration beyond about 40mph. At first he thought this was somehow connected but fault remained after brake repair. Computer showed up a faulty Boost Pressure Sensor which he replaced to no effect. He has checked for leaks, tried replacing the MAF, loosened off the VNT vanes which seemed stiff but nothing works.

Does anyone have any idea where the fault might be?

Graham

Reply | Report as offensive | Link
Fri 28 Sep 2012 18:28
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - craig-pd130

Could be worth checking the vacuum pump on the engine is still working. If it's still hissing it's probably working OK, in which case it's likely to be a hole / split / leak in the main hose from vac pump to brake servo and engine vacuum system, or one of the other pipes or connectors leading from it.

Reply | Report as offensive | Link
Fri 28 Sep 2012 19:08
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - grstephen

Thanks for the tip, I'll get him to check that if he hasn't already done it.

Reply | Report as offensive | Link
Sat 29 Sep 2012 11:47
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - dieselnut

Here is a link to the vacuum pipe arrangement for the Passat, it uses the same engine so will probably be very similar for the Sharan.

https://sites.google.com/site/1810martin/home/b5-vacuum-hose-diagram

The vacuum pump is probably working or the brakes would be very hard.

Probably just a leaky hose.

Reply | Report as offensive | Link
Sat 29 Sep 2012 13:13
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Peter D

I think the OP is referring to a hiss form the actual back pedal i.e. the seal around the servo actuator. I suspect the servo diaphragm and the only fix is a new servo. Regards Peter

Edited by Peter D on 29/09/2012 at 13:20

Reply | Report as offensive | Link
Sat 29 Sep 2012 13:25
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Peter D

http://kfz-tech.de/Engl/Bremskraftverst.htm

Regards Peter

Reply | Report as offensive | Link
Sat 29 Sep 2012 14:29
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - craig-pd130

Servo has already been replaced, however ...

Reply | Report as offensive | Link
Sat 29 Sep 2012 17:27
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Peter D

We do not know what "after brake repair." actually was. The OP needs to clarify and detail where the hissing noise it coming from. The hissing is getting mixed up with the limp mode. Regards Peter

Edited by Peter D on 29/09/2012 at 17:29

Reply | Report as offensive | Link
Sat 29 Sep 2012 23:19
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Big John

At that age the 1.9pd uses vacuum for EGR, variable vane control and anti shudder. Both EGR (egr!) and variable vane control (over boost) problems will put it into limp home. Does the engine shudder on turn off? (Great diagram dieselnut!)

There should be a vacuum T connector on the brake servo feed pipe that is connected to small diamater pipes that feed the engine control vacuum systems. Could it have been disturbed when the brakes were fixed! - With the engine running disconnect the small diameter pipe and listen for a hiss? If present then refit and check for the same at the various solenoids that control the above systems.

For me these faults are too much of a coinsidence after the brake works/servo replacement.

Edited by Big John on 29/09/2012 at 23:34

Reply | Report as offensive | Link
Sun 30 Sep 2012 09:16
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Railroad.

Also check closely the large vacuum pipe to make sure it's not split at the joiners. I replaced one very recently on a Seat Alhambra which had done exactly that. The pipe must be completely air tight, and so must be the smaller vacuum pipes.

Reply | Report as offensive | Link
Sun 30 Sep 2012 12:49
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - dieselnut

An excellent link Peter. It was always a grey area for me as to how the servo worked.

The operation shows how atmospheric pressure enters the servo via the brake pedal rod.

If this was at all restricted I guess it would produce a whoosh noise but not affect its operation unduely.

Reply | Report as offensive | Link
Sun 30 Sep 2012 13:58
1.9 TDI 2003 - VW Sharan power loss, hissing brake pedal - Peter D

There is often a foam noise suppressor and a loose sleeve gaiter. The noise is not normally notice except when bleeding the brakes and using extended travel. As I said a split diaphragm will create a hiss from the pedal. Regards Peter

Edited by Peter D on 30/09/2012 at 13:59

Reply | Report as offensive | Link