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

[tDignam]

Is it the MAF?

2004, BEW (PD), VNT-17, RC1+ Tune

I first notice a buzzing sound, followed by the boost coming late. I've only experienced full limp mode one time.

I took some logs of blocks 011 and 003, both before and after disconnecting the MAF.

Before:

After:

EDIT: Fault Codes

Any ideas? Questions?

 

[nadroba]

I think the electronic actuator is bad or maybe you have a stuck vnt.

 

[TDI_lover12345]

Limp mode, please help?!

I have an '03 Jetta TDI manual transm. w/ 440k km. that started off with not responding to throtle in March, to whick my mechanic said was due to something inside the engine and the fuel pump ( suggested cost of repair - $1,500 to $3,000 ) but said that I could still drive it for a while.

Now, my car has gone into the so called "LIMP MODE" with the loss of the turbo kick ( especially on hot and humid days ) accompanied by black smoke from the exhaust. The car drives ok ( meaning, no turbo kick but drivable on flat roads, loosing power while going uphill ) if I keep the turbo from kicking in at 1800 rpms and cooler days.

Does anyone have any suggestions as to what I'm dealing with in both cases and apprx. costs that I should be expecting for repairs in Toronto, Cnd.?

Thanks in advance!!

 

[ymz]

Get a 2nd opinion...


Yuri

 

[cr4zy3lgato]

I"ve been having problems lately with my car. I have a P1556 code (negative deviation).
I heard a pop when i was on a highway and now the car makes a successive sound like a snake or pressure cooker (like a pss****) as soon as i get over 2-3psi

My mechanic tested for leaks with a smoke machine and found nothing. I have tested the actuator (6 months old vnt-17) it moves well and holds vacuum for a while. I have tested the N75 valve with vacuum gauge hooked to N75 output, i cycled the valve with vcds and at 99% i had no vacuum and at 0% there was near 20mm Hg... i was expecting the same thing, except i thought it would be the opposite...

MAF and vacuum lines has been replaced last year & turbo this winter.

Thanks

EDIT: did'nt get any CEL (only knew there was a code when i scanned it) and after i cleared it and drove the car (still same problem) there's no code???
the interior of my vacuum hoses are also slightly dirty

 

[cr4zy3lgato]

The boost pressure gradually fell to 0psi. It turns out that a bolt came loose on the egr cooler, and the pipe form the turbo to the cooler snaped in the accordeon.

Replaced the part and now it's running fine

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[Bill McCracken]

2002 Golf TDI

I have owned this car since new and have had maintenance done by a mechanic who specializes in VW's since the warrantee expired many years ago. Timing belt has been replaced twice along with the tensioners and waterpump. Car presently has 317,000 kilometers on the odometer. The mechanic has been good however his business has grown to the point that I wonder if he isn't starting to behave like a dealer. (There is now a front end employee writing sertvice orders so I no longer get to talk directly to either of the 3 mechanics.) I have had power problems (going into limp mode I think) over the past year and have had a new oxygen sensor installed, then vacum lines replaced. Last visit I was told he rerplaced the Oxygen sensor (under part warrantee) and cleaned the wastegate because it was sticking. I was told that if the limp mode (and or check engine light) returned the turbo/wastegate assembly would have to be replaced at a cost of nearly $2,000 since turbo and wastegate are sold as one assembly. Unfortunately limp mode has returned although shutting off the ignition and restarting clears the problem temporarily. Sometimes the check engine light comes on - sometimes not. Sometimes the light goes out with the ignition reset and sometimes the light remains on until the engine has cooled down or isn't driven for 24 hours or so.
All this makes me wonder if my mechanic is being straight with me.
Does my car actually have a wastegate? Can it be replaced separately?
Any advise?

 

[Bill McCracken]

Is there more than one type of limp mode. When the car was quite new I once experienced an extreme loss of power (couldn't drive over 50km/hr and VERY little acceleration) Limp mode I'm now experiencing is much lass drastic. It usually occurs on a hill and a definite noticible loss of power occurs like a switch was flipped. It's still possible to maintain highway speeds but with less power so the car slows down on hills etc

 

[Corsair]

I'd recommend (perhaps in future) start your post in its own new thread, to avoid getting lost in the pile of dialogue.

Is the car a TDI (diesel) or perhaps a 1.8T (turbo gas?). Reason I ask is because that vintage TDI does not have an O2 (oxygen) sensor. Perhaps the sensor was mistakenly named? Or if you do have a 1.8T, maybe a different forum would be more helpful, as this one is dedicated to diesels.

If you have long history with that shop and trust them, maybe time to assert yourself and request a conversation with the mechanic you know, maybe you can get some traction by emphasizing the length of time you've been trying to get the problem solved.

To your direct question- sorry I don't know for sure whether there is more than one limp mode. For ALH TDIs (those include year 2002), I've only ever read of one limp mode. But I'm not an experienced professional mechanic- just a back yard wrench.

Wish you all the best.

 

[turboii]

i too having 1556 code - intermittent. Low power when wot and i no longer hear turbo whistle. I checked the vacuum out of the N75 valve with the Vagcom toggling the solenoid, and it checks out ok at about -20 inHg. I can feel the actuator at the turbo moving slightly, but doesnt seem to be opening all the way.. but i do not really know how far it is supposed to move. I also logged manifold pressure and it stays a 1000mbar at wot. I assume its not a boost leak because of the lack of turbo whistle. Does that sound like stuck VNT vanes or bad turbo? 178k miles

 

[dbo550]

Anybody seen this problem. No boost until 2800rpm then fine until next startup.

Ive had this car for 2 years now and its done this since day 1. 2002 jetta gls tdi 178k. once I hit that 2800 rpm car boosts fine until I turn it off and start it again. My problem doesn't seem to be the same as everybody elses in this thread.

 

[ymz]

Sticking vanes inside the turbo? Once they "let go" they appear to work until you stop...


Yuri

 

[Inline4]

My car, 2001 VW Beetle TDI 5-Speed manual. Without warning felt like someone stole my turbo, not hearing that familiar "whine" when accelerating and lack of my normal power. Seemed like I was driving my 1982 Mercedes 240D. My hand held diagnostic tool did not identify the fault code (P1556), service manual gave the code description. I searched the web and it lead me here. Very helpful link. To make a long story short, it cost me $4 to fix. Replaced the vacuum tubing from the N75 solenoid to the turbo actuator. That's mor like it!! Thanks Canadian Grizzley!

 

[slickfast]

I have a question about the vacuum that is created by the vacuum pump. I hooked up a mity vac to the line coming off the check valve of the brake booster (this was as close to the vacuum pump as I can get), and the vacuum eventually builds to >25 inHg but it takes at least 2 or 3 minutes to do so. Is something wrong with my vacuum pump? Just replaced the turbo actuator and it doesn't cycle on startup like it should. I believe I've adjusted the turbo actuator rod correctly.

 

[slickfast]

Turned out to be a piece of gunk in the check valve of the brake booster line that was preventing any vacuum pressure to the turbo actuator. Power restored!

 

[whitedog]

Turned out to be a piece of gunk in the check valve of the brake booster line that was preventing any vacuum pressure to the turbo actuator. Power restored!

Glad we could be of some help.

Really, nice job on troubleshooting. You knew something was wrong and dug in to find it.

That would probably have been a $200 bill at the dealer.

 

[slickfast]

Glad we could be of some help.
Really, nice job on troubleshooting. You knew something was wrong and dug in to find it.
That would probably have been a $200 bill at the dealer.

Thanks a lot for putting the knowledge out there... you were right on the money with boost issues.

My recommendation for anyone that's at the end of their rope: get systematic. I got a hand vacuum pump with a gauge on it (mity vac) and printed out the vacuum line diagram for my engine (alh, stock). I went through every line with a vacuum pump and checked that it would hold vacuum, and when it did I traced the corresponding line with a green sharpie to show that I had checked it and that it was good. After that I went through the check valves and T fittings to make sure they weren't working. The brake booster check valve is pretty much impossible to diagnose with it on the car, so I just took the 2 minutes to remove it. Main booster line was totally fine, but I couldn't get the turbo line to actually allow air through it... weird. Tried sucking on it (next time I'd recommend grabbing the right fitting and using the hand pump) and YECH: dirt and crap ended up in my mouth. Then grabbed a needle, bent it to a little "J" shape and dug the rest of it out. Blew on it again and now it freely allowed air through. Boom, that was it.

Even though the check engine light didn't go out right away I knew I had fixed it, because for the first time in forever I could hear my turbo. SO HAPPY.

 

[SmoothVW]

great post

 

[kblee27]

I've read the first page till the last. My TDI has a persistent P1550 code.
I've tried, checked, some replacement, almost everything. N75 solenoid, MAP, MAF, actuator, vacuum lines. Nothing.
Except I can't reached to clean the turbo or intake manifold.

However, I did note that when I plug the full vacuum into the actuator, I get boost. When I put it back to N75, nothing happens. I only get very small boost of about 5 psi.

Finally, after a couple of years of driving with low boost, and suspecting the boost control problem, my workshop change the ECU.
Instantly, the boost came back.

So it was a defective ECU which did not control the N75.

 

[rdkern]

What type of car?
Do you have the vac lines going to the proper locations?

 

[Joe Cool]

AFTER LOADING A MILD TUNE very mild my trans is now only using one gear. I guess a limp mode sorta.
I put the stock tune back in but of course its the same. I do not know what the fault code is. I was considering buying the VAG Com but have never used one before.

Will it clear a trans code..because I think this is what happened.

Thanks

 

[JASONP]

AFTER LOADING A MILD TUNE very mild my trans is now only using one gear. I guess a limp mode sorta.
I put the stock tune back in but of course its the same. I do not know what the fault code is. I was considering buying the VAG Com but have never used one before.

Will it clear a trans code..because I think this is what happened.

Thanks

That automatic tranny won't hold up to any sort of tune , made that mistake years ago with my 01M


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[Lensdude_com]

I've seen a lot of posts lately of guys breaking bits on their cars by trying to make them perform better...
I suppose the real problem would be one's personal definition of performance!

 

[CoolAirVw]

AFTER LOADING A MILD TUNE very mild my trans is now only using one gear. I guess a limp mode sorta.
I put the stock tune back in but of course its the same. I do not know what the fault code is. I was considering buying the VAG Com but have never used one before.

Will it clear a trans code..because I think this is what happened.

Thanks

You might just need to clear codes. Try a OBDII code tool if you have access first.