Underboost

[SPIKEYJIMBO]

Have had issues with limp mode and garage took it in replaced egr valve and cleared the vanes, havnt had any problems for around a month, however on my way to midhurst the car went into limp mode. Scanned with vag com when I came home and got code

17964 charge pressure control negative deviation d1556 35-00

Ross tech states it's underboost does anyone have any more info on this

Many thanks in advance

[seatkid]

Sticking vane actuator or leaking vacuum pipes most likely suspects I think.

 

Under boost means that the turbo boost pressure (measured by the TMAP sensor) didnt get up to the required value within the time allocated. In other words, the turbo vanes didn't get to the right position either because they got stuck or the vacuum moving them in the vane actuator was lacking.

 

There is an illustrated guide somewhere on the forum that shows how to check the vane actuator movement and how to lubricate/free it up.

Edited March 9, 2011 by seatkid

[SPIKEYJIMBO]

Cheers Seatkid

Apparantly had overboost to start with,took it back to the dealer and they cleaned the vanes which I now know they used an additive to free them up. Now I have underboost.. The warranty is up on the car but im talking to the dealers regards fixing the issue as its still boosting and both over and under have the same possible causes and solutions. I have the vag com print out and the ross tech definitions for the stored code so its going baack to the dealer for them to rectify as it wasnt originally sorted when the warrany was current.. Do you guys think that im being reasonable here.? :)

 

Many thanks

[chrispb123456]

Hi Jim

As you had the vanes cleaned then they need to check all those vacuum pipes and possibly N75 valve this controls the turbo actuator, this is hidden behind a small heat shield on the bulkhead behind EGR valve.

[SPIKEYJIMBO]

Hello Chris,

Thought the n75 and egr valve were the same thing shows you how much mechanics I know :) .. Do you think its reasonable for me to ask this of them? My understanding is it went in with a fault under the warranty and hasnr been sorted so it should still be covered.. heard getting the vacuum pipes replaced would be a good start and you have confirmed that, do you know where they can be brought other than the dealers and what sizes are needed as a google search didnt really give me anything.

[chrispb123456]

Hi Jim

Have attached a pic of the vacuum pipe layout may make things a bit clearer for you.

The N75 valve is what controls the actuator rod which operates the vanes on the turbo.

N 239 and N 18 control actuators on the EGR valve.

[chrispb123456]

Hello Chris,

Do you think its reasonable for me to ask this of them? My understanding is it went in with a fault under the warranty and hasnr been sorted so it should still be covered.. heard getting the vacuum pipes replaced would be a good start and you have confirmed that, do you know where they can be brought other than the dealers and what sizes are needed as a google search didnt really give me anything.

Of course they will try to get out of doing it, but take it back, have a moan as long as it's covered by the warranty thats what your paying for.

 

Good luck. :)

 

Chris

[SPIKEYJIMBO]

Chris,

Cheers for the diagram.. Car is back at the mechanics and he is satisfied its the same issue as before so even though the warranty is up the issue wasn't rectified when it was in warranty.. Really glad I got a vag com and managed to print my scan results, the mechanic was miffed that I had a printed copy :) and also meant that he had no way way to back out of the work by saying no codes stored.. When I get the car back I will let you know what the outcome was.

 

Thanks again all.