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

ASV sticking?
Can you read the codes?

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.

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

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?

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?

I’d replace maf clear codes and see how it goes. Maybe test or swap n75 too. The 1904 code might be low manifold pressure.

Check that the turbo actuator holds vacuum.

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.

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.

bigjake said:

Before I jump right into buying a new MAF, .................

Click to expand...

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.
VW TDI Search Engine

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?

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.php/16683/P0299/000665

JB05 said:

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.php/16683/P0299/000665

Click to expand...

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.

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??

bigjake said:

The filter was a little dirty and there was some junk underneath the filter consisting of leaves, dead bugs and pine needles.

Click to expand...

One of the vacuum hoses from the N75 goes to a port on the bottom of the air filter box.
If the hole in the box is plugged then the N75 might not be able to release vacuum correctly.

I don't recall seeing a port on my airbox. My N75 has three connections to it. One is the vacuum supply, one goes to the turbo actuator and the other operates a butterfly valve on the EGR cooler (don't know the proper name of it).

However, I will say that when I tested the N75 with the vacuum gauge, it supplied a constant 20.5 hg pull. I did not see it switching on and off like some videos on the internet?

The hose nipple opposite the two nipples on the N75 that go to the turbo/vacuum supply goes to the air box. If it is going to the EGR cooler that could be the problem or at least a problem. It needs to vent to the atmosphere.

As JETaah indicated, vacuum supply goes to the top port.
Turbo goes to the one under the vacuum supply.
The single port on the opposite side goes through a tee to the air filter.
The 3rd port on the tee goes to the lowest port on the EGR control solenoid.

The port is on the bottom of the air filter box.

I don't have a single nipple facing the opposite direction. I only have three nipples all pointing towards the passenger side. I additionally do not have any nipples on my air box. I removed it and looked all around it and I have none. Keep in mind this is a BEW and not an ALH. I've owned this car for almost four years now and I don't ever recall a hose going from the air box to any part of the vacuum system, let alone the N75 and I've never experienced limp mode due to any vacuum hoses whatsoever. It's always been a boost leak in the past.

I'm about stumped. I'm going to tear the car down tomorrow and double check the turbo piping to double check for air leaks. When I checked the piping recently, the engine was off and I just checked for tightness. I'm going to fire the engine this time and physically feel around the connections for air leaks. If I don't feel anything, I'll be officially stumped and I'll begrudgingly take it to a mechanic for a diagnosis.

I just looked on ID-Parts and the N75 for the BEW engine does have all the ports on one side.

The lowest port should vent as mentioned.

Well folks, I finally got a day off with some nice weather. I got around to tearing the car down and checked all the piping from the airbox to the ASV. No leaks whatsoever.

So lets review:
1. I installed a brand new Bosch MAF. No difference. ****however, if I unplug the MAF, both the new and old ones, it does not go into limp mode but it does not have full power either. It kind of drives in this weird halfway mode.*****
2. Scanned the car with a scan tool and it's only showing the underboost code. No other code are accompanying it.
3. Tested the turbo actuator with a hand vacuum pump. Actuator responds with healthy range of motion.
4. Tested the N75 with a vacuum gauge and it happily pulled a consistent 20.5 hg at idle (I did not see it switching on and off like some videos show it doing?). All hoses leading to and from the N75 are showing no leaks/cracks.
5. Felt around all the turbo piping and felt/heard no leaks at all.

I changed the timing belt within the last 300 miles before the symptoms started. I have not yet had the timing value set back to spec, so its somewhere around TDC.

Is there ANYTHING else you all can advise me to check before I admit defeat and take it to a mechanic?

bigjake said:

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.

Click to expand...

I'm not clear, but did you tee into the line going to the actuator or hook the gauge to the N75 port leaving the actuator disconnected?

I would tee into it.
With my 03 I had about 10 inches (or so) at idle and it would drop when I took off.
Yes it sounds backwards.

Not sure if the BEW operates the same.

I'm having a very similar issue ('03 ALH all stock) - and I have VCDS so everything checks out ok but still i get limp due to overboost on long fast hills. actuator holds vac and moves fine. N75 tests and cycles fine. One thing i noted though id when cycling N75 in basic 11 and graphing the boost actual barely changed and boost specd. showed just on and off with the cycle. Can MAF alone cause this?

bigjake said:

.............................................
4. Tested the N75 with a vacuum gauge and it happily pulled a consistent 20.5 hg at idle (I did not see it switching on and off like some videos show it doing?). ................................................

Click to expand...

Connect(tee) to the vacuum line to the actuator, you should see it cycle when you drive at speed.

bigjake said:

.............................................I changed the timing belt within the last 300 miles before the symptoms started. I have not yet had the timing value set back to spec, so its somewhere around TDC.

Is there ANYTHING else you all can advise me to check before I admit defeat and take it to a mechanic?

Click to expand...

Verify(set) timing using VCDS or equal.

peteguenther said:

I'm having a very similar issue ('03 ALH all stock) - and I have VCDS so everything checks out ok but still i get limp due to overboost on long fast hills. actuator holds vac and moves fine. N75 tests and cycles fine. One thing i noted though id when cycling N75 in basic 11 and graphing the boost actual barely changed and boost specd. showed just on and off with the cycle. Can MAF alone cause this?

Click to expand...

Have you tried running with the MAF unplugged?

Rob Mayercik said:

Have you tried running with the MAF unplugged?

Click to expand...

If you are doing ALH basic settings at idle it will not change hardly at all. The ECU has not raised the engine speed and it won't create boost. It simply cycles the N75 so that you can see if the actuator and N75 valve is responding. The cycling should pull the actuator down to the stop screw at 100% duty cycle and release it back to home position at 0% (or close to it) duty cycle.

Update.

No, I did not T into the actuator line. I simply unplugged the actuator line and hooked my vacuum gauge directly to the N75. However, going back and trying that would be irrelevant at this point, because I bought and installed a brand spanking new Pierburg N75. Went for a test drive and hit limp mode above 40 MPH. I'll be returning that N75 now thanks to Amazon's lenient return policy, lol.

I do not have VCDS nor do I know anyone who has it. So I'm unable to check timing values. No one has still answered my question, though, that if the timing is off far enough, will the motor freak out and go into limp mode?

At this point, I've checked absolutely everything I can think of and that you all have recommended. I'm absolutely stumped and admit defeat. I've scheduled an appointment with a VW mechanic in town who will look at it Friday for a diagnosis only. I'll let yall know what it ends up being.

Without a proper scanner, not a code reader, it is not possible to diagnose it properly.
Throwing guess a parts at it could get expensive quickly.

If you have a laptop you only need to buy an OBD cable that works with VCDS lite to diagnose it.
The lite version is free and does 95%+ of what you need.

Hey guys, I took the car to a local European car shop (not the stealership) for a diagnosis only. The mechanic looked everything over and stated everything was functioning the way it should. Vacuum, MAF, timing, actuator/wastegate solenoid, etc. His diagnosis is the turbo itself is just plain ole worn out and needs replacing. This is a KP39 and I'm pretty sure it's the original with 307,XXX miles on it. He believes the fins are wore out but he didn't bother to pop off the exhaust pipe and physically check them. I was bothered by that, but he claims he's been doing this for years and that everything that regulates the boost system was functioning as it should so there is likely no other cause but the turbo itself. They knew from the get go that I was going to be doing whatever repair job myself, so they shouldn't have had any incentive to lie to me as to what needs fixing in order to make money off me.

I'm a little confused because it appears, from what I've read on here, that KP39s tend to die in the form of boost creep causing overboost. Mine is underboosting. Does this guy's diagnosis sound right? If so, VNT-17 upgrade on the way soon.

Wonneber, I do have a laptop. It runs Linux Ubuntu, however, which is not compatible with VCDS. The only VCDS versions I've seen are only formatted for Windows and Apple. Even if I had it, I don't know what to make of all the data I'd be seeing. Threw a hail mary with the N75 because of Amazon's super lenient return policy and I'm getting a full refund, so the only loss here is time.