[TDI2000Zim]

OK, there are perhaps 7 ways to generate the P1556 code (I've only hunt down 2 of those, without finding any cause). Is there a way to tell the ECU not to report it for 500 miles, so that I can drive around for a week worry free, instead of 50 miles?

I feel bound to my town because of this.

 

[chittychittybangbang]

other than fixing it? Not that I know of. You could use more gradual application of power.

http://wiki.ross-techcom/wiki/index.php/17964/P1556/005462

17964/P1556 - Charge Pressure Control: Negative Deviation
Boost Pressure too Low
Hoses/Pipes incorrect connected, disconnected or leaking
Charger Pressure Control defective
VNT (variable nozzle turbo): nozzles stuck
Solenoid Valve for Boost Pressure Control (N75) defective

Look through the FAQ article on limp mode

 

[TDI2000Zim]

Thanks!!!!!!!

BTW, after so many years I did learn the hard way not to use the turbo .

 

[TDI2000Zim]

Besides intermittent, I notice that this problem occurs more frequently when the day gets hotter (as in, the previous day was cooler; if it is overall hot for a few days, this doesn't happen that often). So, outside air temperature gradient is involved.

Question - What is more likely to act up because of higher temperatures, the N75, the Charge Pressure Control, or the turbo's Variable Nozzle?​

By the way, treating the accelerator like a 'newborn babe' helped me drive without getting the P1556 flag to turn on for 700+ miles.

I'm checking this: http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm

I found the following, which both apply to my case, since my VCDS says "17964 - Charge Pressure Control: Negative Deviation/P1556 - 35-10 - - - Intermittent":

1a. Boost Deviation Intermittent means you most likely have a vacuum leak somewhere. Check all vacuum lines, turbo actuator, and plastic fittings. There are vacuum lines that connect the turbo, car computer, sensors, etc., and tend to get frayed at the ends or rub through.

1b. Boost Deviation Negative means you have a clogged intake, turbo actuator that's leaking, bad vacuum lines, or a sticky turbo actuator lever. If you have a VNT turbo, it may be because of stuck VNT vanes which requires removal and cleaning of the vanes.​

Gosh, this sounds like it is 'hosed'. Checking/replacing all those hoses sounds like fun... Still, this doesn't explain why it acts up when a heat wave hits my town. On the plus side, this sounds like the N75 is innocent of wrongdoing.

 

[chittychittybangbang]

Maybe the hose gets soft and bends enough to let air through. These are usually the turbo, vacuum lines, solenoid, electrical wire, or other.

 

[fstjetta]

Have you done a boost leak test? The vacuum lines are pretty easy to check. They normally split at the ends or rub through somewhere.

 

[rmchambers]

Replacing vacuum hoses is not hard !IF! you take your time and do them ONE HOSE SECTION AT A TIME. take one piece off, make a note of where it went, measure the new hose and replace that section, fasten it if the old one was fastened and continue on to the next.

I did that when I first got my "new to me" Jetta, the old hoses were dry and cracking and the new blue silicone ones look tres sexy!