P1556 code is driving me nuts!

Hey guys how are you doing? I have a 2001 vw jetta tdi with the auto trans. Recently it's been throwing the p1556 code. I have all new vacuum lines, brand new turbo, new maf, the map checks out, the n75 checks out and the actuator on the turbo is working. I am stumped! Anything that I could be missing here? Any advice is very much appreciated!

Did you check for leaks in turbo piping you could have a leak somewhere on the boost pipes or maybe on the intercooler.

1.4TDI PD said:

Did you check for leaks in turbo piping you could have a leak somewhere on the boost pipes or maybe on the intercooler.

Click to expand...

I will check the intercooler next. That's about the only thing I havnt yet. But, I did look over the hoses and seems as if they are all connected right.

That code came up for me when my intake was plugged.

Tdijarhead said:

That code came up for me when my intake was plugged.

Click to expand...

Intake is nice an clear. It has the egr deleted. I just put the turbo on and I checked the intake.

Sorry, thinking of a different code I believe

Alright well I just checked the intercooler and turbo hoses and nothing seems to be leaking. I'm at a loss here...�� any suggestions?

Check the ross-tech wiki site for that particular DTC. They will offer suggestions.

JB05 said:

Check the ross-tech wiki site for that particular DTC. They will offer suggestions.

Click to expand...

Already have.

Does it smoke black on high speeds?

A faulty map sensor could do that too.

jasantos40 said:

Does it smoke black on high speeds?

A faulty map sensor could do that too.

Click to expand...

It did before I changed the turbo. I havnt noticed afterwards.but the map checked out on vcds.

I've seen sensors reading wrong values and not pulling DTCs.

A VCDS log on wot would help.

Spec intake pressure VS actual intake pressure, n75 cycle and maf flow.

jasantos40 said:

I've seen sensors reading wrong values and not pulling DTCs.

A VCDS log on wot would help.

Spec intake pressure VS actual intake pressure, n75 cycle and maf flow.

Click to expand...

How would I go about checking that threw vcds? I'm new at it and dont know a whole lot yet.

Measuring blocks, you have a block that reads actual intake pressure. Group 11.

jasantos40 said:

Measuring blocks, you have a block that reads actual intake pressure. Group 11.

Click to expand...

I actually have a video monitoring blocks 10 and 11

Post it!

jasantos40 said:

Post it!

Click to expand...

[URL=http://s75.photobucket.com/user/fowla2007/media/Screenshot_20180821-124220_Video%20Player.jpg.html][/URL]

Instead of throwing parts at the problem, you could try doing some diagnosis. The link is for a BRM engine, however the ALH turbo is very similar. Your boost pressure looks a little high which means the stop screw on the turbo is not adjusted correctly.
https://www.myturbodiesel.com/wiki/turbo-stop-screw-adjustment-tdi-engine-zip-tie-engine-hesitation/

To check, go to basic settings for charge pressure control (group 11). The high number from the test should be about 1050

Diisclaimer: the link addresses a BRM engine and for an ALH, the values may be different.

Did you check the vacuum system and components for integrity and proper operation with a Mitet-Vac?

I know you "replaced all vacuum lines" but have you actually tried MEASURING how much vacuum your car is putting out?

Put a vacuum gauge to the small diameter port on the check valve between vacuum pump and brake booster, see what you get.

Very common to see that plastic pipe to the booster split and cause a big vacuum leak. Also not uncommon to see a leak caused by the vacuum pump itself. The large port on the vacuum pump works its way loose and doesn't seal adequately after awhile.

If you're not getting at least 20" mg vacuum at idle, you're likely to get some underboost. A proper healthy system normally puts out more than 25" mg. I see a lot of ALHs with 15" or less because of leaks at the pump or the pipe to the brake booster... That will absolutely cause underboost.

Just a update. I have the problem fixed. I recently remove the egr an cooler from the car. So I delete all the extra vacuum hoses for those and I must of had a line switched around. Now all is good.