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P0102 Where would you start?

5K views 22 replies 2 participants last post by  billymade 
#1 ·
Hello there. New member. Bought 2001 Bug 130,000 miles for the daughter from good friend. Long time VW nut and last car I bought was 2003 Passat that sludged up ad sold. So I know a few things...

The story: wife's friend drops the car off and says drive it for a weekend and if you like it, buy it. Drove it and fell in love again. Even the crayon smell. Ran great but needs brakes... CEL was on but after cleared nothing for 1 week. Of course after we pay for it, she starts acting up. Ran rough at 1/4 tank. Based on my research it is fuel pump time so filled the tank and runs fine 1 week. Rough running on start now (starting to cool down now) and heavy gas odor. I replace ignition coil and all is fine a few days. Car stalls on drive to school today and pending P0102 on Bosch scanner I have. I take inventory of service records which are insanely detailed. Plugs etc 5YO. MAF sensor, throttle body, and other similar things all replaced within last year. Someone has been chasing this issue I think…

Sensing I need to up my game now and contemplating VAG COM $200 setup to properly diagnose and help with since it appears a few people were taking stabs at it. Would love to take that money and stick it into brakes, pump, etc. (yes OEM). I am not really a garage monkey but do plan to do all but the major stuff myself. I can see however, this tool may be good to have around. Really curious just how much more detail VAG COM would be. Any advice or suggestions appreciated.
 
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#2 · (Edited)
Well, welcome back to the VW world; after taking a break, from what I assume was a notorius 1.8T Passat failure!

As always, start with the fresh scan and check out the code in the ross tech wiki:


We have had many maf issues over the years and as noted, watching live data makes a big difference with a scan tool like the Ross Tech VCDS. There are many VW scanners on the market these days but the industry standard is VCDS, it will pay for itself many times over, by enabling you to complete "diy" repairs and not be beholden, to the VW dealer or other pro auto repair shops. The ability, to maintain control of your troubleshooting and repair process; with VCDS, is essential to maintain these Volkswagens. VCDS, is the real deal, a mature product, used by pro VW techs the world over and the support offered by Ross Tech, by a dedicated USA based support team, is priceless! :) They offer call in tech support and a registered user support online forum; that is great, offering solid, advice and solutions, for VCDS users. The cheaper Chinese knockoff "VAG" scanners; have little or no support, so after purchase you are essentially on your own. While, OBDEleven, is a newer VW/Audi scan tool; that has come up recently, it doesn't offer the level of maturity, it is in many ways a ongoing beta/development product and with support from the company in eastern europe, they are no where near as responsive as Ross Tech.


Troubleshooting the maf, would be helped by viewing live data, following the maf troubleshooting/testing page on ross techs site and logging the results, to see if it is reading in spec (2nd gear @ WOT):


Fuel trims, are also; a quick and easy way, to see the current tune of the engine:


We see mafs have a issue with the plug or wiring terminal ends; causing a intermittent connection issue. While observing live data; you can do the "wiggle test", by wiggling the wires/plugs, to see if the signal drops out or changes. If that is a problem, you can buy a new plug and terminal ends; at your local VW dealer or they sell plug/pigtail combination repair kits on ebay or amazon (I would recommend the genuine VW parts; for the best, long term, reliable repair).

Lastly, if you end up needing a new maf; stick with oem Bosch and buy from a reputable part supplier, to be sure you don't get a cheap aftermarket or counterfeit Bosch auto part. You can look up the right part number; on their website here:


So, the Ross Tech VCDS is highly recommended; it sounds like you have some testing to do and report back, what you find out. Thanks! :)
 
#3 ·
Yes, Passat 1.8T fail. I think since it was wife's driver and tons of short trips (live in small town) did it. Probably would have been fine for someone commuting to work or if I realized it needed synthetic. Boy that car was a cool tho. Silver wagon and crazy 2nd gear to about 100mph.

Thank you for the excellent info and your time. I have researched my issues and see many of your posts. This makes me proud and reminds me there are more good people on this rock.
Not looking for a tutorial but am I going to be driving the car with VCDS running and laptop connected to test MAF via VCDS? I assume there is a way to record the data. A little worried of the learning curve to use but I am becoming familiar of the live mode testing and what it does. I also am aware of its limits, does not do fuel pressure etc.

Lastly, where for parts? Amazon is trusty? On deck is fuel pump. Definitely going OEM and looks straightforward to do but a little weirded out how to clean the clean tank. I guess seal breaks down. No idea how I will clean it up. I will do filter as well anything else? Thanks in advance.
 
#4 · (Edited)
Hey, VCDS, has allot of depth to it but the new user challenge, is understanding the info/data, it allows you to see, then interpret this info and solve your problems, by making a diagnosis of the problem you are having (e.g. "normal" range of say; the maf sensor).

Many features and info; are documented on the ross tech site and you can download the VCDS users manual there as well:

data logging:

VC SCOPE: for live data streams and graphing:


User Manual:


It maybe easier; if you have a helper to watch the live data on the computer while you drive, using the measuring blocks feature (look at the ross tech maf testing link for info) but logging or seeing the scope data later, could be done by yourself. Much to learn and try out; testing the maf is discussed in the tech bulletin linked to above:


The other good thing about VCDS; is there are many youtube tutorials, outlining many common tests and procedures.


Parts sources, can be found many places; the KEY is to stick with high quality oem parts like Bosch, VDO, NGK, etc. Online, everywhere from Amazon, Rock Auto, ECSTUNING, RMEuropean, AutohausAZ, shopdap, and many others are good places to buy. FCPEURO, is unique; in that they offer a lifetime warranty on their parts and so, while tend to be a bit more then the cheapest prices online, when you parts fail, you will get new ones for free.

For the common maintenance parts; you can typically find the oem parts at many auto parts stores, some stores like Autozone, will offer oem vw parts from their commercial parts desk or through special order, from the warehouse (many come the next day) and keep any eye on online discount coupons, to save money that way. While, we generally, don't recommend the Duralast brand of parts; many times, you can find genuine vw parts in the Duralast brands boxes (go figure; for example the Duralast new beetle window switches are genuine vw; they are cheaper at $35, then what you can get them for @ your local VW dealer for $50 or more, plus they come with a lifetime warranty!)

Stay away, from cheaper house brands; that are sold at many auto parts stores, they can be cheap aftermarket chinese knock offs and these can cause havoc with your Volkswagen and cause all the kinds of drivability issues (e.g. Airtex fuel pumps, cheap relays, etc.).

I buy online, if I am not needing the part right way but Amazon, can be another good source, if you have free quick shipping through Prime. I can get genuine vw parts; from my vw dealer next day and same for Autozone, for oem parts as well (the commercial desk; offers a wider range of higher end oem parts for sale/order).

If you are unsure about a part; if it is original, you typically can find the brand on it, next to the VW/AUDI logo, that is the OEM. OEM parts, can be purchased cheaper, then from the VW dealer with a substantial savings and many times, it is the identical part, to the original. Check out these links; to learn about oem parts suppliers and parts availability, cost savings:



Most of the better european/vw parts specialists; suppliers online will sell the oem parts by default but others, like ECSTUNING, sell the really cheap stuff too (stay away from HAMBURG TECHNIC, URO, MTC, other chinese knockoff low grade parts).

If you have questions about the best parts and oem brands to buy, let us know and we can recommend the oem supplier, good places to buy the parts and prices, you can expect. Thanks.
 
#5 ·
Thanks again and great links! For now I think I will wait until for VCDS due to learning curve but am learning more about OBDII and now realize I need to consider the drive cycle. I have printed the Snap On drive cycle in one your posts. It's actually pretty wild... Downshift etc. As I mentioned, car is basically never driven on highway so I think I will need to do some of that to rule out problems with MAF as is part of EVAP, right? Scanner show 0 DTC but incomplete codes for EVAP and Catalytic. No emissions test here but want car 100%. While I am at it, vacuum leaks will throw MAF codes right?
 
#6 ·
Some good news. Managed to complete a drive cycle and all INCL are gone and in READY status. Been a long time since I was in the mood to just drive, but it IS a VW... Also, no new codes but there is still some acceleration issues even with full tank and fairly certain it is fuel pump and/or filter. OEM assembly and filter in my Amazon cart. At this point I have seen enough videos to change it I could probably do it in my sleep. From what i can tell I do not need to drain and clean tank unless inspection shows clear issues. IE seal has disintegrated or flashlight in tank shows funk. Sound good?
 
#7 ·
Well, that is good; that your "readiness" tests have passed and that helps, rule those issues out. What I am not clear on; is other tests you have performed, to confirm, that other parts are in spec or need replaced? Here are some, I would perform and confirm, before replacing parts. I recommend testing and confirmation of bad parts; rather then, throw parts at a problem and hope, it is the issue, by essentially guessing or shotgunning, bringing out the "parts cannon", assuming they will address the issue you are experiencing. You might be lucky or you might be replacing a non defective part; considering, the age, miles of the vehicle; MANY parts, could be suspect at this point.

Testing:

MAF:


fuel pump:


We have beaten many of these issues to death here on this site and in many ways, we probably sound, like a "broken record" with the repetitive nature of the testing that is recommended. The fact of the matter is; you must check the basics and confirm, where the problem lies. Unfortunately, there is no "silver bullet" or "magic", when it comes to troubleshooting and testing things.

Let us know, the resutls of your testing or any trouble codes, we can go from there. Thanks.

PS: if you do decide to buy a new fuel pump; stick with VDO or Bosch, the Bosch tends to be the best bang for the buck; as its design, includes the fuel tank level sending unit and they include a seal for the tank locking ring, for the pump. In the case of the VDO; the sending unit and seal; are not included and must be bought seperately, adding to the total cost of the repair. Other items, that should be replaced; are the fuel filter and the fuel pressure regulator; which will have the same wear, in the case of the filter possibly clogged, this will essentially refresh the whole fuel delivery system, aside from the injectors themselves, which typically do not need replaced, until they malfunction or stop working (some people; like to add some fuel condition, to clean the injectors for good measure).
 
#8 ·
Happiness short lived and back to basics now. Multiple stalls and P0725, P1780, P1850, annnnnnnnd good ole P0102. Cleared codes and disconnected MSF. Will do some driving, run some tests on it with multimeter, and report back. I am a little weirded out by how often a stall etc occurs and yet no CEL, code, or even pending one.
 
#9 ·
Always, pay attention; to your trouble codes:





All the definitions, should be looked over and analized, start related testing procedures. The one code, that stands out; aside from the MAF, that you have mentioned before, is the engine speed/crank sensor, this can defintiely fail and cause, a dying, hard start, no start issue or just dying, then starting right back up issue.
 
#10 ·
P0725 VOLKSWAGEN - Engine Speed Input Circuit Malfunction

If you decide, to go ahead and replace the crank/engine speed sensor; stick with oem BOSCH, DO NOT, buy/install a cheap aftermarket chinese parts. Stick with high quality oem/vw parts and you will have better results, long term reliable repairs (do it once; do it right!). You can look up the correct part #; for your car here:


For best pricing, you can typically find them online (e.g. amazon, fcpeuro, rockauto, etc) or locally, check for online coupons @ pepboys, autozone, oriellys, advance auto, etc
 
#11 ·
Thanks. I can't find an answer (and it might be obvious but not to me) but are codes stored in order? IE P0725 is first code that appears in reader, so is that the "first" code?

Yes, going OEM all the way now. I like to save money but the amount of posts I've read where people had bad luck is pretty clear now. I too also noticed ALOT of similar problems to mine on speed sensor threads (many with no stalling and no DTC). $30 on Amazon so I snagged it and an Mann fuel filter to play with.
 
#12 · (Edited)
That is a good question; it maybe a situation where, the "freeze frame" data stored in the ecu, could provide info about that, although i don't know if it records the date/time, when the fault occurred? You would assume, he codes would be displayed as they occurred or in the order of the various controllers in he vehicle was scanned in succession, it would then be displayed.

Freeze frame obd II:


We still don't know, what scan tool; you are using, what brand/model did you get? I assume it is a generic obd II scanner and not vw specific; as you are posting non vw factory codes but just generic obd II types.
 
#13 ·
While searching on ebay I stumbled across a Bosch unit for $28 shipped. Pulled the trigger too fast. Ebay said last one and I made the unfortunate assumption that Bosch meant VAG support but I now know differently That said, have already used the scanner on other vehicles so it was not a complete waste. Definitely getting VCDS but would prefer to wait a until the bleeding slows... Just paid for car, brakes, and stereo on deck. I will pick it up if I start losing my patience. I wish they had a 1 VIN package for $66 (199/3) or even $99.

Same stalling issue exists with MAF disconnected but no codes thrown (besides MAF for being unplugged). Interior of connector is a bit chewed up but does not appear to pose an issue. Had no time for DMM testing.

I am a little bit relieved to see pretty much all functions of the car appear to work including the heated seats and rear defogger. Didn't expect that.
 
#16 ·
That was nothing. Totally secure but did not look like it.

UPDATE: Installed crank sensor yesterday. That was much harder than I anticipated... Sore today LOL. Just finished a drive cycle and no codes and all ready no incl. Probably my imagination but it feels as though that it is driving better than I remember. Wasted half a can of start fluid testing for obvious vac leaks but none found. Gonna run the tank down and it misfires at 1/4 tank it will get a fuel pump,
 
#17 · (Edited)
Good progress; keep us in the loop, I hope this crank sensor, ends up being a fix for your drivability issues and a needed repair! :)

PS: the crank sensor; can be a bit of challenge to get out, I think I used a small prybar, to pop mine out of my 1.8T (it was the original one). [emoji41]
 
#18 ·
Biggest issue I had was it was so hard to see. No way I could have done it from top and had to do from bottom. The old sensor rotated well and just took a few moments of patience to work loose. I probably got some cred from my neighbors watch me. It looked like I was changing the tranny or something LOL.

Back on the fuel pump. Do you feel a visual inspection of the tank with flashlight will properly assess whether the tank is funked up with debris?
 
#19 ·
As noted before, i pulled my defective fuel
pump; then, i noted the fuel tank locking ring seal was jagged and literally falling apart from the ethanol in the fuel. As i was removing things; small rubber debris was falling into the tank (frustrating); i took a closer look with a flashlight and it became apparent, there was debris collecting on the bottom of the tank. Unfortunately, i had recently added fuel and so, i bought a squeeze bulb type siphon kit. I removed the existing fuel and this allowed me to clean out the rubber seal debris. Be sure to use lint free cloths or paper towels.

I guess it depends on the brightness of your flashlight but i was able to see the bottom of the tank and the black rubber debris, that had settled there, no problem.
 
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