Dreaded Limp Mode w/ P1557 Error Code

A while back I was driving up a steep grade on the highway and once I got to 65mph there was a dramatic loss of power but at that time no check engine light. I bought a scanner, got the P1557 "Charge Pressure Contr. Positive Deviation" code and have done the following since.

• Replaced the Boost Pressure Control Valve
• Replaced the EGR Pressure Converter Valve
• Replaced the air filter
• Replaced the fuel filter
• Checked and found no vacuum leaks

A dealership mechanic says it might be the Mass/Volume Air Flow High Circuit or the turbo itself - which was rebuilt three years ago when I also have the manifold removed and steamed cleaned as well. I could replace the Mass/Volume Air Flow High Circuit, but that was done back in 2011 and I'm not convinced it's the issue right now.

From what I've researched, it sure seems like the vanes on the turbo are clogged at the high boost position and thus the limp mode. Does that sound correct? If so are there good turbo cleaners out there or am I facing removing the turbo and having to do it by hand?

At least the car is functional but just not on highways at the moment.

Good step-by-step in my sig.

Or search on "limp mode" for even more details.

Carbon Beyond the Turbo?

Thanks for the references. I feel like I get the technical aspects of the problem now. I did find a mechanic willing to give me an hour's worth of diagnostic time with their sense was it was carbon build up behind the turbo with a $1000 price tag to explore and clean it all out.


Seems reasonable (doing the work myself is impossible right now) but I'm still confused in that back at 180k the turbo was rebuild and the manifold steam cleaned. How does carbon build up in only 24k effect boost such that I'm now in limp mode again?

Well, there are *many* things that could be causing your limp mode besides gummed-up vanes, but if it is gummed-up vanes some variables would be:

- the quality of the "rebuild" itself... specifically were worn parts replaced, or just the rings cleaned? If cleaned... fully disassembled, or with oven cleaner or another shortcut?
- is the car driven hard frequently, getting EGTs up there to burn off the normal build-up, or is the car generally babied along, gently accelerated, shifted at 2500, mostly short trips, etc?

I trust the rebuild. It was done by a shop that only handles VWs and often older ones.


The biggest differential has been moving from Portland, OR to Boston, MA where driving in the fashion you described, and the other all much colder weather could be factors.



About to disconnect the MAF sensor as you decsribed to see if that's the issue. If not, then I've pretty much narrowed it down the carbon build up - regardless of how strange that feels after only 24k of driving.


That said, when this new mechanic said the carbon buildup could be "behind" the turbo (exhaust etc.) causing back pressure which send the TDI into limp mode, that sounds like a rational description. To my knowledge there's been no cleaning of anything outside the engine and turbo during the 204k life of the car.


Oh, and changing my driving habits based on your suggestions. Vroom, vroom!

Yeah you need to red line this thing once a week......you gotta drive it like you stole it.
Actually prior to you doing this for the first time , disconnect the lower intercooler pipe and clean out any pooled oil there , if not when you do stomp on it the increase in volume of air can and will take that accumulated oil into cylinders #2&3 and possible give you a mini runaway or enough oil a hydro lock.
Not meant to scare you but it has happened , especially when people just cleaned their intakes but not the boost pipe.....just my .02

BIOTDI1375 said:

About to disconnect the MAF sensor as you decsribed to see if that's the issue. If not, then I've pretty much narrowed it down the carbon build up - regardless of how strange that feels after only 24k of driving.

Click to expand...

Could be worn/rusted out/maladjusted actuator as well... unless I missed you ruling that out earlier. This is particularly possible in climates with lots of rain, salt on the roads, and/or no belly pan on the car, as the actuator is very exposed under the belly of the car.

Good video in general, around the 10 minute mark he gets specific about actuator diagnosis, including showing what it looks like after the turbo's been pulled.

https://youtu.be/02KJxNnYiZk

Both are great videos. Very detailed. Other's I've found online also do a great job to show how and why vanes get clogged with carbon thus making the actuator not travel the full distance.



I disconnected the MAF and that only make overall performance worse so it's onto the actuator and of course carbon build up. Which puzzles me the most. How is it that so much carbon could get built up in 60k miles? That just seem strange to me that the turbo and manifold could be so thoroughly cleaned and then for this to happen now.


Who knows?