Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

I have the lite version which said "17964/P1556 - Charge Pressure Control: Negative Deviation".


From Rosstech
17964/P1556 - Charge Pressure Control: Negative Deviation
Possible Symptoms

• Reduced power output
• Limp mode

Possible Causes

• 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

Possible Solutions

• Check Hoses/Pipes to/between Components
• Check Solenoid Valve for Boost Pressure Control (N75)
• Check / Clean / Replace Charge Pressure Control
• Check / Clean mechanism for variable nozzles

I would check adjustment of the turbo actuator.

In addition to the adjustment of the turbo actuator, I would check the compression while you are in there, popped turbos can bend rods.

alphaseinor said:

In addition to the adjustment of the turbo actuator, I would check the compression while you are in there, popped turbos can bend rods.

Click to expand...

Cheers for the heads up guys. How would you do the compression test or repair the rods?

You would need a compression tester with the proper adapter and gauge. The kind you hold in a spark plug hole won't work. The adapter would go in the glow plug hole.

To repair the rods, you would need to disassemble the engine.

doesn't really sound like a bent rod to me, it's throwing an underboost code so I'd check the vacuum to the turbo, check the actuator to see it moves freely. check to see it moves with vacuum (hook up a mighty vac). Other thing to check, it happened to me, is the EGR valve is sticking, clamp off the EGR hose to force it out of the picture. (though that last one seems less likely)... what's likely is a vacuum leak caused by the turbo replacement.

Cheers guys. Really appreciate the help. Getting the vacuum hoses done tomorrow. Will check back in there. Thanks.

Got the vacuum hoses changed. Wow what a difference. Back to normal. He also said he cleaned the intercooler out as there was a LOT of gunk in it. The garage who did the initial work said they cleaned it out but obviously lied.

Took it for a spin and had full power up to 90mph. The car is driving a little rough at 60mph+. Any ideas? Wheels balancing? Bushings? A low an behold, as I was on the way home from the garage the brake pad warning light comes on. SIGH!!!

Isn't car ownership fun? Glad to hear that things are progressing.

Yeah love it especially when I'm pulled over on the side of the motorway with smoke covering the entire road!!

Brake light gone off though. Weird. Cheers guys!

Time for a visual inspection of the brake pads.

Shoot me now please!

Hi,
My wife’s 2003 Jetta has been experiencing limp mode, 120k miles. I’ve read through portions of this thread numerous times. Yesterday I threw my hands in the air and brought it to a mechanic.
The car was throwing no codes. I replaced all the vacuum lines as it seemed to be worse the hotter it got. Nothing changed. I swapped out the NP75 dealio with the other solenoid and still no difference. The actuator was pretty rusty looking so I threw a new one of those on(I could barely get the old one to move when in my hand). I thought that might be my problem, but no, still no boost. I read about the oven cleaner trick, tried that, still nothing. The impeller on the exhaust side moved freely before I did the oven cleaner method.
So it took awhile for the mechanic to figure it out. Because it was blowing blue smoke out the exhaust he came back and said it could be 2 things, worn rings or clogged intercooler. Turns out the intercooler was full of oil. He told me the oil was coming from the turbo, worn seals.
Sound right?
So, not one willing to piss away over $2k, I’m looking at options and I have questions. I have heard not to buy a remanufactured turbo. Is that true? I can get a new aftermarket turbo and intercooler off of ebay for under $500. Total crap? I can buy a new Borg Warner turbo off of ebay for $750, aren’t those OEM?
Part of me is afraid to do any work in this car myself, not that I can’t do it but this car seems to want to be the death of me.
Any insight fellas? Do I need to replace the oil lines while I’m in there? Other than the exhaust manifold are there any other gaskets I might need?
I appreciate your time and comments.
Walter

I thought about starting a new thread but thought I would keep it here incase my scenario might help someone else.

....so the mechanic went for the big bill first.
How much oil have you been adding between oil changes?
What are your oil change intervals?
Did you remove the turbo outlet hose and try to wiggle the impeller?
If so, how much wiggle room in/out as opposed to left/right?
The OEM turbo is a Garrett VNT 15...the Borg is OEM on the BEW engine (KP39)

Oil level appears fine, I have never added any. I change the oil every 3k-5k depending on my schedule, trips planned, etc. I removed the the exhaust side of the turbo when i did the OC trick. That impeller moved freely, not certain about the play as I could only get one finger in there.
So the Borg will work for my 03' jetta?

the oil level appears fine and the intercooler was full of oil? I know the engine isn't capable of producing its own oil so the intercooler was NOT full of oil or the intercooler accumulated oil over the last 120K miles from the PCV (puck on the valve cover) through the turbo inlet pipe.
Are you using synthetic or conventional (dino) oil?
If conventional oil was used then you might find a partially coked turbo oil feed line or excessive cylinder wear from sticking piston rings.
If synthetic oil but not DIESEL rated synthetic oil was used then soot would cause excessive engine wear throughout.
At this point I would remove the RF wheel and turbo outlet pipe so you can get your thumb and forefinger in there to grasp the nut on the end of the impeller shaft and give it a push pull...any movement is bad

I am using synthetic for diesels. Maybe "full of oil" was an exaggeration. I did go into the shop where the car was on the lift and the mechanic had the tube off of the intercooler. He stuck his index finger in there and it was covered in oil when he pulled it out and the tube was well oiled also.
I'm ready to drive this car off a cliff.....Alright, pull the front wheel check the impeller. Will do thank you, I'll report back.

chickenhawk said:

I am using synthetic for diesels. Maybe "full of oil" was an exaggeration. I did go into the shop where the car was on the lift and the mechanic had the tube off of the intercooler. He stuck his index finger in there and it was covered in oil when he pulled it out and the tube was well oiled also.
I'm ready to drive this car off a cliff.....Alright, pull the front wheel check the impeller. Will do thank you, I'll report back.

Click to expand...

There will always be a light coating of oil inside the intercooler hoses and inside the intercooler itself. That is normal. What is of concern is if the intercooler has a lot of oil pooled up inside. I'd consider anything more than 1/4 cup to be "a lot".

Lots of slow driving, idling, short shifting and light throttle will leave more oil in the intercooler. Giving it a good amount of throttle and running the engine up to 3-4000 revs regularly will blow the oil out of the intercooler.

Here is how I check to see how much oil has collected in the intercooler without removing it.

With the car up on jacks, remove the lower intercooler hose. I use hose clamp pliers on the big clamp and pull the hose off.

Take a 6-8" long screwdriver and stick in into the intercooler port until it touches the bottom of the intercooler. A piece of dowel, piece of wire, etc would also work.
Note the port is angled at about 45deg, you want the screwdriver at the same angle. Don't let the screwdriver touch the side of the port, if you do you'll get oil smeared all over the shaft and mess up the measurement.

Pull it out, keeping it at the same 45 deg angle. Now you can see how deep the puddle of oil in the intercooler is.

A 1/4" deep puddle is probably around 1/4 cup. Anything more than that and you're either driving like a grandma or possibly have the turbo seals leaking oil into the intercooler.

Thanks Todd-Given what I saw at the mechanic shop i would say there is more than a 1/4 cup of oil in the intercooler.
Everything I have with a motor gets worked hard. This is my wifes car and she does drive like a granny. I do drive her car on occasion and open it up, but maybe not enough.
I still need to check the impeller shaft as Lensdude_com suggested. Problem is it;s too early to start drinking......

chickenhawk said:

Problem is it;s too early to start drinking......

Click to expand...

I'ts noon somewhere...Mark

chickenhawk said:

This is my wifes car and she does drive like a granny. I do drive her car on occasion and open it up, but maybe not enough,

Click to expand...

Some think that to "drive it hard" means they must drive at all times like a crazed maniac at high speeds. Not so.

All that is needed to periodically run the engine up to 3-4,000 rpms with 80-100% throttle. Freeway onramps are excellent for this. I shift normally into 2nd, then run the engine up to 3500 or so in 2nd and 3rd with close to full throttle. 3500rpm in 3rd is just about 60mph, perfect for merging into traffic.
Doing this a once or twice per trip or at least a couple of times per week is enough.

This procedure results in high exhaust flow which blows oil out of the intake tract (so it doesn't accumulate in the intercooler) and helps keep the VNT vanes inside the turbo from getting jammed up which is one cause of overboost and limp mode.

RacerTodd said:

Freeway onramps are excellent for this.

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Ain't that the truth? Where I live, there is a stop sign at the end of the block, then a right turn and about 30 yards to an on ramp to I-10. This is where I used to scare the heck out of my passenger in my 912, without breaking any laws (except maybe excessive acceleration ). I doubt if my Beetle will ever build up oil...Mark

About once a month i get to drive her car without her in it. When she is with me, I always get a funny look when i put my foot into it. At least now my heavy foot can be justified. Ever tried using "turbo cleansing" as an excuse for speeding when pulled over by a cop?
Yesterday I had a string of bad luck. Kids computer crashed, I couldn't fix it. I went to go harvest honey from my beehives and got stung through my bee suit and my armed swelled up and hurt like hell all day. I went into the bath room to rub some salve on my bee sting and the jar fell out of the medicine cabinet and shattered my sink basin.
After that I told my wife, "if it can break I ain't touching it today". So sometime at the end of the week I'll dive into the turbo and see if the impeller has any free play. I will report back and have questions.
Thank gents!

chickenhawk said:

About once a month i get to drive her car without her in it. When she is with me, I always get a funny look when i put my foot into it. At least now my heavy foot can be justified. Ever tried using "turbo cleansing" as an excuse for speeding when pulled over by a cop?

Click to expand...

No need to speed. My method maxes out at 60mph in 3rd, so as long you're doing it on freeway onramps "the man" should be no problem.

Just explain that a new turbo equals 10 pairs of shoes and she'll be hammering up the onramps in no time!

So I was able to do some wrenching this morning. I got my fingers on the impeller shaft. No noticeable play. There was slight resistance but it did move freely. I pulled the lower hose on the intercooler and about 2 cups of oil came pouring out and lots more in the bottom of the intercooler. Could the oil be coming from the turbo even if there is no play in the impeller? Could those seals still be shot with no play?
There was a slight hesitation about 1/8 throttle lately. I thought it might be the TPS(if these even have one) and did not think It was related to this issue. My wife drove the car into work earlier in the week and said the hesitation and idle where getting worse.
I do know since I brought it into the machanic last week there is WAY more oil in the intercooler. My wife maybe put 30 miles on the car this week.
Any insight on where the oil may be coming from? Any thing else you can suggest I look at? Know of any reputable TDI mechanics in the Missoula area? Know of a nice cliff I can push this car off of?
Thank you.

Edit: I went out and checked the CCV. It was clear. I stuck my fingers in the impeller shaft again.....there is a minute amoutn of play. Maybe a 32nd....64th? So small you can barely notice.

https://docs.google.com/document/d/1Lucw8ALCkLtt79MMw9JOG1E_dX57-raBhbhIFdtHnEQ/edit?hl=en_US
There are two on this list that are in Montana.
The excess oil that you found in the intercooler could be from a partially blocked turbo oil return that's causing excess pressure in the turbo labryinthe seal...this also means that someone has been adding oil between oil changes.

Thanks Dude! Unfortunately both of those listed in MT are a good distance away from me.
No one is adding oil, I'm the only one that works on our vehicles until last week when I took this TDI into a mechanic.
Could the worsening hesitation and the recent(more oil since the mechanic)excessive oil in the IC be related?

Nothing deflates my ego more than telling my wife I have no idea what is wrong with her car. I put it back together and took it off the jackstands. I started reading about "runaway" and now I don;t even want to drive it.

So was that a no, if the impeller on the turbo has no play the seals are fine?

no... impeller shaft play means bearings are fine but I have heard that a boost leak can cause oil to be drawn into the charge-air path

Hey All,

Been reading around a ton and this is the best thread to diagnose my issue. I'm only getting limp mode when I gun it up a hill. Here's the code I'm getting:

16618 Boost Pressure Regulation: Limit Exceeded (Overboost Condition)
P0234 - 35-00 -

I was reading through the first post in this thread and have ruled out vacuum lines. I'm in the process of checking out the actuator and VNT. I read this and was wondering which one this fault code falls under?:

"There are three common codes for limp mode.
Boost Deviation Intermittant
Boost Deviation Negative
Boost Deviation Positive

Boost Deviation Intermittant means you most likely have a vacuum leak somewhere. Check all lines, actuators, and plastic fittings.

Boost Deviation Negative means you have a clogged intake, actuator that's leaking, bad vacuum lines, or a sticky turbo.

Boost Deviation Positive means you have a N75 that's bad/malfunctioning, actuator that's leaking, bad vacuum lines, or a sticky turbo."

Any advice would be great!! THANKS!!

and you can do all that with a vacuum pump like the MityVac...in the meantime, just select a lower gear moments before you have the impulse to gun it up a hill