17964/P1556 - Charge Pressure Control: Negative Deviation

**kenney** · 06-03-2011,10:54 PM

judging the log,the pressure is correct only when the revs reach 3000,which does indicate a leak somwhere,

**Jamiem** · 06-03-2011,11:39 PM

It's a definate leak, but where I don't know. I think it has to be the N75 letting air through when it shouldnt, I've just double checked, and can definately blow air back through the N75 when all is off, so I think I'm gonna take a punt at one of those.

**Crasher** · 07-03-2011,12:02 AM

I must admit to becoming confused with this recently. If you do a component (SDC) code search for an N75 valve on a AVF/AWX engined Passat 3B it says that there are three alternatives which is rubbish but one is listed as “pressure converter (for turbocharger)" which is shown as 1J0 906 627 A, 1J0 906 627 is listed as being "Pressure converter (for exhaust gas recirculation)" but plainly you have pulled this off the bracket in front of the turbo which is the N75. I tried to get VW TPS Nottingham to clarify this for me and they became as confused as I was.

**Jamiem** · 07-03-2011,12:14 AM

funnily enough when i did a google search on the part number i found the same thing. I had a link to an online parts catallogue and it was described as a pressure converter for the EGR, but yes, it came off the plate at the front of the engine. Do you think my diagnosis sounds correct of it being fubar'd?

**Crasher** · 07-03-2011,11:00 AM

It is possible the N75 is faulty but if it operates on an output test I would suspect not.

**Jamiem** · 07-03-2011,11:30 AM

The picture you posted yesterday of the vac hose under the inlet; is that the first point in the chain? Ie if I vacuum from here there should be no leaks? I need a starting point to work from to check each hose and connection in the chain. What I don't get is why there is a connection open in to the air box? This seems to allow air in wherever I suck/blow from.

**Crasher** · 07-03-2011,11:47 AM

Yes, if you carefully detach the vac hose from the servo pipe (they can break which is annoying) and apply a vacuum to that hose it should be air tight with a few pumps of a hand help pump. I use a Mity Vac for the initial test and if I detect a leak, I use a Pella pump to provide a constant vacuum whilst searching for the leak.

**Jamiem** · 07-03-2011,11:57 AM

I've got access to an oil siphon unit at work, but it's so bleedin loud that I doubt I'd hear the leak from the engine bay! I'm going to do some more prodding at lunch time, remove that hose under the inlet and see what I can find. Driving to work this morning was dire - it went in to limp mode every time I was just cruising.

**kenney** · 07-03-2011,12:27 PM

1jo906627a is the turbo pressure converter and 1j0906627 is the egr pressure converter,so jamiem you have either read the part number wrongly or you have the wrong valve,been down tis road before