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TDI 101 Got a simple/basic TDI question? Are you a newbie (new to the forums). Feel free to post your question here.

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Old April 30th, 2008, 21:35   #1
kayak01
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Default Turbo Underboost

I took my 04 jetta wagon to a local mechanic for the check engine light. Code 16683 - turbo underboost. What does that mean? How do I fix it? and how do I keep it from happening again?
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Old May 1st, 2008, 01:02   #2
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Underboost is where the computer requests a certain amount of boost, and the turbo delivers an amount less than requested.

The '04+ have much better vacuum lines, so that's "probably" not it... my bet is on the VNT actuator, loose vacuum line, or an N75 valve.

Most PD engines won't clog the intake like the VE engines, but who knows... might as well pull the EGR valve and take a look.
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Old May 1st, 2008, 07:05   #3
gforce1108
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The vacuum lines might be better, but they are certainly not great... On my '04, the line from the N75 to the turbo wore through where the dealer routed it wrong (EGR recall). Check that line and go through your intercooler tubes. The one at the top (EGR connection) pops out very easily. There's a nice repair kit selling on the forums. I also added thicker orings in every connection from the turbo to the engine to prevent boost leaks.
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Old May 1st, 2008, 08:01   #4
kayak01
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Thanks, I'll try all of that as soon as it stops snowing. Is it a bad idea to keep driving until she's fixed?
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Old May 1st, 2008, 08:15   #5
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It's probobly not too bad, but that means the turbo is trying to produce as much boost as it can, pretty much all the time. It's lot of work for it.
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Old May 1st, 2008, 09:37   #6
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If I understood my VAG-COM logs correctly, the N75 was trying to make boost all the time, but the turbo was not, since the actuator was not moving correctly. Mine slowly got worse as the line rubbed through more, eventually going into limp mode and throwing a code.
If there was a boost leak it would be much harder on the turbo.
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Old June 5th, 2008, 15:12   #7
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I have the same problem, but it's too hot out to work. I wish I were in Jackson Hole.
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Old June 5th, 2008, 23:56   #8
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Too bad we never found out if kayak01 solved his problem.
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Old June 6th, 2008, 09:32   #9
d2305
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Driving up a 8000 ft. mountain will suck up the fuel. He's lucky to get 38mpg. I looked at all my vacuum lines and hoses, and they all look good. Guess I need to find a guru.

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Old June 8th, 2008, 20:06   #10
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if all of the hoses and lines checked out ok try checking out your VNT actuator....the diaphrams in them have been known to fail (mine is borderline right now...does not hold perfect vacuum)....if it can't hold vacuum then it wont move the vanes in the turbo to create boost.
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