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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old May 8th, 2019, 05:33   #1
bigjake
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Join Date: May 2015
Location: Charlottesville, VA
Default Limp mode out of nowhere

Hey guys,

So I drove my car to work last night (work night shift) and I had no issues. Just another commute. This morning when I got off, I went out and started my car. I did notice an abnormally longer crank time, but nothing super terrible. They happen from time to time. Aside from that, I left work and everything was going normally for the first several miles which is city driving. As soon as I started climbing the foot of a large mountain, there it was. Limp mode. I recalled a time last fall when I got my car into limp mode because I left off the key too early when I was starting it. It sputtered, I hit the key again and it started but was in limp mode right out of the gate. I killed the engine, restarted, and the problem was gone. No other limp mode incidents until today.

Thinking that today might be similar, I pulled over, killed and restarted the engine. When I merged back into traffic and started going up hill, everything was normal again until I hit 3rd or 4th gear, then there it was again. I drove most of the way home in limp mode. I eventually gave it another shot towards the end of the drive. While moving, I shifted into neutral, killed and restarted the engine. I didn't have any issues for the last few miles.

What concerns me is, usually my past limp mode experiences are coupled with a very obvious hiccup (boost leak, letting off the key early), but today was out of the blue and they were back to back. I fear something else is at play here. I do not hear any boost leaks and I did not see black smoke pouring out while in limp mode, so I do not suspect a bad MAF sensor. I do have a CEL on, but that's because I deleted my EGR years ago and have been too broke/lazy to get it deleted off the computer.

This is a BEW with an 09A transmission. 299,000 miles. Any usual suspects I should look at?

-Jake
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Old May 8th, 2019, 08:01   #2
JETaah
 
Join Date: Jan 2001
Location: mi 48836
Fuel Economy: 53 max, 42 min, average 46
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ASV sticking?
Can you read the codes?
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Old May 8th, 2019, 11:14   #3
BobnOH
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Join Date: May 2004
Location: central Ohio
Fuel Economy: 50/45/35
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Wiring to the turbo actuator?
What you have now is classic limp mode, what you had before sounds like something else (loose pipes, failing pump(s), things like that.
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Old May 9th, 2019, 20:42   #4
bigjake
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JETaah: I don't think the ASV is sticking. I cleaned it about a year ago after I deleted the EGR. These BEWs have the newer electronic ASVs and I don't think they stick shut like the old ALH vacuum operated ones do. I'm getting VAGCOM and I'm gonna look for codes this week.

I found this YouTube video. Same car as mine and the guy described the exact symptoms mine is having. I'm beginning to suspect the N75.

https://www.youtube.com/watch?v=x7_qLPwVDwg
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Old May 12th, 2019, 13:27   #5
bigjake
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Ok, so I finally got the opportunity to run a scan after a friend loaned me a scan tool. It threw an underboost code (p0299) and a MAF code (P0100). Needless to say I think the MAF is the culprit here.

Thoughts?
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Old May 12th, 2019, 16:43   #6
bigjake
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I also got fault code B1904 which says "Contact 1 in switch for start authorization." I can't find this code anywhere on google or what it means. Can anyone advise?
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Old May 13th, 2019, 04:23   #7
Fahrvegnugen
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Id replace maf clear codes and see how it goes. Maybe test or swap n75 too. The 1904 code might be low manifold pressure.
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Old May 14th, 2019, 10:13   #8
JB05
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Fuel Economy: 43/41/40
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Check that the turbo actuator holds vacuum.
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Old May 16th, 2019, 14:42   #9
bigjake
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Before I jump right into buying a new MAF, I want to focus on the wiring harness I can't find much on the P0100 code, but what little I do find seems to center the issues around the harness. I pulled it off the other day and I only saw 4 of 5 contacts in the harness. It looks like one is missing. I initially thought it got pushed back int the plug, but I don't see it at all. Are BEW models supposed to only have 4 plugs? I know the ALH is supposed to have 5.

I'll check the actuator soon too.
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Old May 23rd, 2019, 12:45   #10
bigjake
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Does anyone have a wiring diagram for the MAF harness of a BEW? I don't have a manual for my car and google yields no results.
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Old May 23rd, 2019, 13:26   #11
BobnOH
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Location: central Ohio
Fuel Economy: 50/45/35
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Quote:
Originally Posted by bigjake View Post
Before I jump right into buying a new MAF, .................
Well that's smart, many of us have spare working MAFs, because we see the code and replace it. The codes are clues, system is not that sophisticated, often it is the wires just not connected good or a different component.
If you have a genuine VCDS, try asking Ross Tech about that other code. If not, it could be bogus.
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Old January 16th, 2020, 22:12   #12
bigjake
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Hey guys,

So I never gave a disposition on this. I tested the vacuum line to the turbo using a hand pump and it was fine. Actuator had plenty range and it was holding vacuum. I turned my attention towards the MAF and cleaned it out using MAF cleaner and boom. Car was completely back to normal.

Fast forward 8 months and 7000 miles later aaaaaand it's back. Same original symptoms as the original post. Car performs fine until the motor experiences significant load (climbing hills, higher speeds, etc.). It hit me on I-81 out of nowhere after I had already bee driving. Keeping this recent experience in mind, I pulled off, bought MAF cleaner and sent half the can through the MAF. Got back on the interstate and no change this time. I pulled off again and unplugged the MAF. This time, the car was in a strange half limp mode. Definitely more power than when the MAF was plugged in, but still less than normal. It seemed to me that the MAF was dead for good this time.

Before buying a new MAF, I tested the turbo actuator and vacuum line again. Still plenty of motion and holding vacuum. Checked turbo piping and didn't find any damage or leaks with all connections being tight and no "wooshing" sounds upon acceleration. I tested the MAF wiring harness with a voltmeter but, I'll admit, don't really know what wires are what as I still cannot seem to find a BEW MAF wiring harness diagram. One wire gave me 5v, one gave 12v and two gave nothing.

The one thing I did know was there is a clear difference in power when unplugging the MAF. Considering this one was at least 100,000 miles old (on it since I bought the car), it seemed reasonable to me that it was dead for good since cleaning didn't affect it. I ordered a new one and put it in today. Drove the car on a test drive and it did fine. I then later left for work and boom. Limp mode as soon as I pulled out on the highway.

I am once again borrowing the bluetooth OBD scanner from my friend and will check codes in the morning. However, I'm worried that it's going to give me the generic underboost code which won't tell me much. I'll advise of the codes after I do the scan.

I also had just changed the timing belt about 300 miles before limp mode struck. Is there anything timing related that can send a motor into limp mode?
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Old January 17th, 2020, 05:47   #13
JB05
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What does ross-tech wiki have to say regarding the P0299 DTC? On my BEW Golf that same code was due to a leaking turbo actuator, which I changed.
http://wiki.ross-tech.com/wiki/index...3/P0299/000665

Last edited by JB05; January 17th, 2020 at 05:49.
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Old January 17th, 2020, 06:25   #14
bigjake
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Quote:
Originally Posted by JB05 View Post
What does ross-tech wiki have to say regarding the P0299 DTC? On my BEW Golf that same code was due to a leaking turbo actuator, which I changed.
http://wiki.ross-tech.com/wiki/index...3/P0299/000665
Luckily it wasn't my turbo actuator last time and I don't suspect it to be this time. It has a healthy range of motion when I apply vacuum and it holds vacuum as well. Last time it was a dirty MAF that cause the P0299 code. Not sure what codes, if any at all are on the computer now. Still haven't scanned it as of yet.
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Old February 5th, 2020, 13:08   #15
bigjake
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Ok guys, update.

I got the scanner from my friend and, as I feared, it gave me a generic P0299 underboost code with nothing accompanying it. Since this last post, I did some tests on the N75 since it very clearly isn't the MAF this time. I pulled the N75 off the car and began to tap the nipples on my counter to see if any debris would come out (saw this in a youtube video). Nothing. Clean as a whistle. Next, I hooked it back up and proceeded to test the vacuum at idle using a vacuum gauge and hooking it to the turbo line nipple. The N75 happily pulled 20.5 Hg consistently.

Next, I decided to check my airbox for obstructions. The filter was a little dirty and there was some junk underneath the filter consisting of leaves, dead bugs and pine needles. I cleaned it out. While unpleasant, this was not enough of an obstruction to cause limp mode. My vehicle does not have a snowscreen anymore, but I checked the pipe that leads down behind the headlight and it was free of obstruction.

So to sum up so far:
MAF - fine
N75 and hoses - fine
turbo actuator - fine
air filter/box - fine
turbo piping - appears fine

What should I look at next??
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