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1999.5 tdi jetta p1550. Im out of ideas

33K views 22 replies 11 participants last post by  almir 
#1 ·
i just bought a 1999 tdi jetta i got it at a great price because the check engine light is on and its running at low power.... limp mode i assumed. i figured it would be a simple fix so i bought it ..... i tinkered with it for 15 hours yesterday and i'm still having the same issue.

code comes up as p1550 pressure control difference.
when i start the car the light is off for around a minute to a minute and a half it drives with full (or what i'm assuming is full power all 90 hp worth) power and then the engine light comes on and it feels as if its not making any boost. (i can still barely hear the turbo tho.)

first thing i did was change all the vaccum lines.... nothing

then i cleaned the intake (it was horrible) still no change.

i swapped the n75 with the egr regulator (i was told i could do it for testing) this still made no difference

i went back to autozone and had the codes cleared . this time it ran for maybe five minutes before the check engine light went on. i went back up and had the codes re scanned and had the same code p1550

next i unplugged the maf this didnt make too much of a difference. some but not much.

the wastegate actuator is working i hooked it directly to the line (bypassing the n75) while at idle and it sucked the rod down around 1/2 a inch maybe a bit more couldnt see too well just feel.



now i'm frusturated and stumped because i figured itd be a easy fix. it might still be i just cant figure it out.

is it possible for the boost sensor to go bad causing the computer to get confused?

how much vaccum should the system be making?

i went ahead and ordered a new n75 but it wont be here til next week. and i'm pretty sure its not the issue.

any ideas would be greatly appericated.

thanks for taking the time to read this .
 
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#4 ·
Vnt's, waste gates lol, I can never tell which car has what. Mine has a waste gate and I went ahead and took it off anyway and cleaned it. I would do the same on your car but I'm like that I guess and yeh it is controlled by vacuum but if it's sticking it wont give it's full range and if it deviates the ecu will just stick it in limp mode I think.
 
#5 ·
i got under the car this time and felt the actuator again it is closer to a inch id say proly 7/8 inch

i ordered a maf a map sensor (boost pressure sensor) and a new n75 i will replace them on tuesday when they get here if not i guess the turbo is coming off.....

i'm assuming that even if there was a leak in the boost hoses that the car wouldnt throw a ce light at idle.. i could see it happening at higher rpm but not at idle.... correct me if i'm wrong
 
#11 ·
VAG Error Code: 17958

EOBD II Error Code: P1550

Fault Location:
Turbocharger (TC) pressure - control difference

Possible Cause:
Intake/exhaust leak.
Hoses interchanged/not connected.
Manifold absolute pressure (MAP) sensor (G71).
Turbocharger (TC) wastegate regulating valve.
Turbocharger (TC) wastegate actuator.
Turbocharger (TC).

As taken from my http://www.myturbodiesel.com/forum/f9/free-eobd-ii-error-codes-software-2919/ ;)
 
#12 ·
SWeet. I was thinking either maf or boost sensor ( im assuming its the same as map sensor). So i ordered both yesterday. Should be here by wensday ill let yall know how it goes.

I assumed it was one of these two sensors because it gives the p1550 error and limp mode even at idle. So im thinking it cant be a leak because at idle theres not enough air flow to make a difference i wouldnt think. Am i correct in my assumption?
 
#13 ·
hy . i had same problem. presure diference. the last think i did after checking all the stuff you did,it was removing the down pipe.turbo was boosting but was no where to go, thanks to a clogged catalitic.is worth the try.remove the 3 screws from the exhaust manifold and youll find right out.
 
#15 ·
Have you solved it yet?

I have a very similar problem with my car so maybe you can figure it out for me. When you were checking the turbo to see if it was stuck, was there any resistance at all? Mine does have some resistance, since everything was still hooked up I figured there should be. Mine also has about an 1 inch of travel. I did check the Cat and it's not a problem. Car occasionally has the 1550 code.
 
#23 ·
turbo leaks

I to have this same problem. Thanks for all the advice. How do you check to see if the catolitic converter is plugged?
I know for gasoline engines the way to check cat for clogging it is to use laser thermometer. Bring engine to normal operating temperature, point a laser two inches before the cat, and 2 inches after the cat. Record temperature differences. If the front is much hotter than the back, you know it is clogged since hot gases are building up and not escaping on time. Another way is to remove oxygen sensor before cat and install pressure gauge, it should not be more than 1.5 psi of pressure. For diesels I assume should be the same test, but the temperatures will probably be much lower .
 
#21 ·
Tree Bug,
did you ever find out what the issue was.. I have the exact issues with my 98 Jetta TDI..
Thanks,
Mike
You'll have a waste gate turbo in your car, it's different to the others, they all have vnt ones. So you're getting a bit of surging then nothing? Just make sure the waste gate isn't stuck, you can try moving it with a screw driver or similar if you can get to it. The other things I would go for would be to replace the vacuum pipes as they're cheap too. Do you have any codes? Do you know if it's over or under boosting? Anyway it's a lot easier to repair on your car. The waste gate on yours works on pressure rather than vacuum, the turbo just spools and the ecu sends a signal to the N75 to open the waste gate to release excess pressure when the boost has reached the desired level. I had the same sort of issue on my previous car so took off the turbo and intake etc, cleaned them out and replaced all the vacuum pipes, the car never had the problem again. It had the AGR engine with waste gate type turbo.
 
#22 ·
I have a 99 New Jetta TDI that gets that code sometimes, but it goes away...
Thrown a lot of money @ the problem, but the solution appears to be to drive over 2700 rpm and vary speed...
Because there is no vacuum advance, acceleration by increasing gas may clog sensors...
It happens when driving uphill a lot...
 
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