New TDI owner with some questions, and a few [car] issues

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I've been browsing for a couple weeks, and I'm very impressed by the TDIclub community. One of the strongest and most vibrant forums I've come across in my years of surfing. Really excited to have this forum as a resource.

A bit of background: I'm a 23 y/o mechanical engineering student, and I have moderate to advanced levels of mechanical experience. Car owner and driver for ~8 years now. In the beginning (and even now) I had to do my own work to save money, and with a happy byproduct of learning a lot! Over the years, I've done almost any car repair possible short of taking the short block to a machine shop for rebuild. I've done many a ball joint, tie rod, wheel bearings, steering racks, brake calipers/rotors/pads, chased down drivability issues, auto to 5 speed swaps, pulled engines, etc.
And it seems like this TDI I just picked up might need all of those things!

Ha, just kidding. It's not quite that bad, but that's what I'm here to figure out.
I just bought a 2000 Golf 4 door GLS TDI (of course) w/153k. Unfortunately it is an automatic, but we will see about that.

I recently picked this thing up as a sad 'toss around' with a broken coolant flange and trans in limp mode.
I replaced the coolant flange, and driven it ~40mi. It starts off in 2nd, shifts harshly into 3rd @4k rpm, then shift harshly into 4th at 4k rpm again. It won't go into 1st gear on its own, nor will it shift into overdrive. It will go into first if I shift it manually.

Additionally, the motor seems to run a little funky at times.
First of all, easiest starting motor I've ever come across! Hit the key for microsecond and that diesel is chugging away.
Aside from the transmission issues, the motor seems to have no power at times. Shortly after start up, seems like it has a huge vacuum leak under throttle. It will approach 2k RPM fine, but when I give it more throttle it has no additional power and feels like when a gas motor has a vacuum leak and it's about to stumble under load. Going up hills (even in 2nd gear) is hard.
Then maybe 30 seconds later, it seems to have its regained mid-top end umph and will pull rather nicely into the higher RPMs.
Even when it feels like it has no power, it doesn't miss a beat.

I haven't found a good way to check the trans fluid as it's a sealed unit, but I did pull the codes. I'm using a semi-professional grade "CPReader Launch 123"
The codes were P0722 -Output speed sensor No signal, and P0730 - Incorrect Gear Ratio.
These codes line up pretty well with my situation.

The seller's theory was that the hot coolant from the broken flange dumped right onto the speed sensor and fried it. Seems plausible, but can't remember the last time life was that easy for me.

Additionally, I went into the 'other side' of the scanner. I don't really know what this is, but it's not the regular OBD2. It's just called 'scan' and it yields a TON more data than OBD2. SRS, ABS, traction control, transmission codes, etc.
2 new codes:
P1144 - Mass airflow sensor short circuit to ground
P1556 - Charge press. ctrl. lower control limit

The MAF was unplugged when replacing the coolant flange. I plugged it back in.
I understand it's common to unplug the MAF to diagnose limp mode, but no idea. Previous owner didn't provide any clues.

A couple issues:
I have no idea what a TDIs is supposed to feel like. I don't know if it is actually low on power or "that's just how they are".
I have zero experience on turbo motors, so no idea how to diagnose charge tubing or a boost leak or anything along those lines.

Thanks in advance for the help!

I would start by checking the connectors on top of the transmission, and check for any cracks or splits in the vacuum tube from the pump to the booster.

Sounds to me like you have two different issues.

With a proper scan tool, you can go into the TCM and monitor some things.

Along with checking the electrical and vacuum connections and parts, order a
transmission fluid and filter change kit from one of the trusted vendors here.
It's really nice to get exactly what you need to carry out maintenance chores.

It's a good thing you like to read this forum because there is a lot to learn and
it sounds like the TDI you have will keep you busy finding and fixing some long
delayed repairs.
Try to get your hands on a real VCDS so that you know what's really going on.

The shifting weirdness sounds like the output speed sensor, all right - just went through that on my 02. Be warned, that sensor is hidden under the bracket that holds the trans mount to the frame, so it's a pain to get to.

There's not a lot of vacuum lines on an ALH, if they don't look too new, might be worth just doing them. Besides the little lines, there's also the line from the vac. pump to the brake booster that can develop leaks (as mentioned above), and the vac. pump itself can leak at the nipple where the hose hooks up.

If you have vac leaks, the turbo actuator may not be getting actuated right, and could be gumming up a little initially, then popping free (which could explain some of the other drivability issues you are reporting).

Leaving that aside, OilHammer and Flee are bang-on: get a VCDS, and start checking out the trusted vendors for maintenance kits. I'll add one more must-have tool - a Mty-Vac or similar (I have the Harbor Freight version), it's very handy on these cars.

Oh, and not to cause alarm, but given the history you know on this, do you have any documentation on when (or even if) the timing belt was last changed? For a 2000, the timing belt for an automatic was rated for 40K miles (was upped to 80K with revised parts in 2002 and then again to 100K in 2003). If you can't prove the age of the current timing belt, the low-risk move would be to park it if possible until you can replace it; unfortunately, I'm not aware of any reliable way to visually gauge how much longer a belt or tensioner will last.

Thanks for the replies, everyone - very much appreciated.

I think I'm more worried about the engine and transmission (mostly because it wouldn't take me too much convincing to go ahead with a 5 speed swap. Oh the auto trans went bad? Damn, what a shame...).
So I think I will look into the vacuum lines first. Are these vacuum lines the type covered in the mesh cloth? I'm away from the car for the week, so I'm doing my research and forming a plan for the weekend.
Should I do anything special? Or can I just go to Advance Auto and get matching diameter line and cut it to length?

About the trans fluid/maintenance, how hard is it to replace the fluid? I've seen some transmissions with no dipstick, but they still have drain and fill plugs, but I've also need some units with a filler but no drain...so you just have to unbolt the pan and 'catch' it.

I do have a Mity-Vac! Somewhat helpful when it works.

The timing belt is the one thing I do know about the car. It has a "Continental" sticker on the core support saying 142k miles or something.
What's odd though is every single TDI I've seen (on Craigslist or whatever) has the same Continental sticker. What's the deal with this?

Will look into VCDS, but I'll admit - I don't want to get too invested with the car. Along with me feeling the pain of out of state tuition, I'm financially conservative by nature. Not sure how much money I can responsibly budget to spend on specialty VW-only tools for a $1300 car.

The cloth covered lines are what come from the factory.
I would not go to Advance, but they might have it.
You can find factory tubes if you want or
Silicone Hose and Viton hose part numbers - TDIClub Forums

The thing about purchasing VCDS or "Vag-Com" has a couple of merits:, 1.) there are usually previously owned ones for sale here at a reasonable price, 2.) should you ever tire of your TDI there is almost always someone wanting to buy VCDS at a discount, and 3.) not having access to VCDS makes it difficult to precisely pinpoint what the problems actually are when they occur.

stomachbuzz said:

Will look into VCDS, but I'll admit - I don't want to get too invested with the car. Along with me feeling the pain of out of state tuition, I'm financially conservative by nature. Not sure how much money I can responsibly budget to spend on specialty VW-only tools for a $1300 car.

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Got any friends with VWs/Audis? You could scan their cars for beer!

stomachbuzz said:

Thanks for the replies, everyone - very much appreciated.
I think I'm more worried about the engine and transmission (mostly because it wouldn't take me too much convincing to go ahead with a 5 speed swap. Oh the auto trans went bad? Damn, what a shame...).
So I think I will look into the vacuum lines first. Are these vacuum lines the type covered in the mesh cloth? I'm away from the car for the week, so I'm doing my research and forming a plan for the weekend.
Should I do anything special? Or can I just go to Advance Auto and get matching diameter line and cut it to length?
About the trans fluid/maintenance, how hard is it to replace the fluid? I've seen some transmissions with no dipstick, but they still have drain and fill plugs, but I've also need some units with a filler but no drain...so you just have to unbolt the pan and 'catch' it.
I do have a Mity-Vac! Somewhat helpful when it works.
The timing belt is the one thing I do know about the car. It has a "Continental" sticker on the core support saying 142k miles or something.
What's odd though is every single TDI I've seen (on Craigslist or whatever) has the same Continental sticker. What's the deal with this?
Will look into VCDS, but I'll admit - I don't want to get too invested with the car. Along with me feeling the pain of out of state tuition, I'm financially conservative by nature. Not sure how much money I can responsibly budget to spend on specialty VW-only tools for a $1300 car.

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In your situation start by correcting the electrical gremlins. The fluid can wait.
But you can damage the auto if it keeps slamming into gears. They don't like that.
It will save you the cost of buying a manual trans + clutch and the labor if you can
save that automatic.

Agreed - address the G68 (output speed sensor) issue first, so the TCU isn't abusing the trans.

Would be a good time to do the other sensor (input) as well, as they're probably both the same age.

Thanks for the input, I appreciate the expertise.

I'll go through the issues in the order recommended.

One question though - if my speedometer is working properly, but I have all the symptoms (CEL codes, trans shifting badly, no OD), is my output speed sensor still to blame?

NVM - I assume on German cars of this era track the speed from individual wheel sensors.

stomachbuzz said:

Thanks for the input, I appreciate the expertise.

I'll go through the issues in the order recommended.

One question though - if my speedometer is working properly, but I have all the symptoms (CEL codes, trans shifting badly, no OD), is my output speed sensor still to blame?

NVM - I assume on German cars of this era track the speed from individual wheel sensors.

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Your car has a vehicle speed sensor in the differential housing portion of the transaxle, and there is the G68 output speed sensor which is the one related to your P0722 DTC. Two different sensors. The VSS is mainly for the speedometer.

Only the later cars, like the A5 platform and newer, have no VSS. Those use a distilled vehicle speed signal from the four wheel speed sensors broadcast across the CAN bus by the ABS module.

There is also the G38 sensor on the transmission, very near the G68.

I would not mess with anything else right now... no fluid, no nothing. Just replace the G68 and clear your DTCs and see how the transmission behaves. It may just be internally tooefed, and the G68 signal is not what it is expected to be, because the guts of the trans are no longer working. The 01M is a turd of a slushbox, so it is not surprising that it could be dead.

However, as I stated in post #2, check the plugs on top, as the G68 plugs in remotely, next to the round plug that goes to the internal trans harness. You may just have a worn/chaffed wire going to that sensor.

oilhammer said:

the G68 output speed sensor which is the one related to your P0722 DTC. Two different sensors. The VSS is mainly for the speedometer.

There is also the G38 sensor on the transmission, very near the G68.
Just replace the G68

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thanks for putting it in plain English for me.
I'm on a vendor's site and I see 3 possible G68 sensors.
I understand at least one of them is the older style, but not sure which one is for my car.

Thanks

https://www.idparts.com/transmission-components-c-29_103.html?page=2&sort=3a

also, is the G38 the VSS on the diff?

Also, is there anyway for me to just check the sensor without doing all the trans bracket removal stuff?
Check for chaffing, broken wires, or check the continuity of the sensor

I replaced the G68 trans sensor. The only issue I had was getting the trans mount to bolt back in straight. I found the bolt holes for the trans mount were actually slotted, so it could move as the bolts were being torqued down. I tried to ‘muscle it’ to keep it straight, but it ended up crooked anyway.

So the trans definitely acts better, but still issues.
First of all, I now have 1st gear back. I also have overdrive AFAIK. Can now hit 70mph, but it’s around 3000 or 3500 rpm (can’t remember which). Hard to imagine any speed over 75mph. As mentioned below, when at low speed/RPM, it ha no power, but it pulls quite nicely when it actually gets into high RPm.
1) still no power down low. Takes off very sluggish.
2) when being sluggish, it gives slightly more power until 1/2 throttle. If press anymore in the pedal, it just falls flat.
3) Still shifts hard. It shifts much earlier than the previous 4000 rpm bang shifting. Sometimes mildly rough, sometimes quite alarming.
4) when slowing down, it will shift back into a lower gear and start engine braking. So, will coast fine, then 40-50mph it automatically downshifts and seems like the TC locks up because the engine RPM matches and it starts to engine brake.
5) when in D, and it’s not doing the engine braking silliness, sometimes it sits at ~2k RPM when I am off the throttle. Put it in N and it settles fine at 850rpm.


In my experience, almost all these are symptoms of low fluid, but I’m always keen for a nice surprise.

Something still sounds off - I'm turning about 2600-2700 at 70 on the speedo.

Wonder if the "fuzzy logic" is messed up due to the sensor... did you reset the trans computer after doing the sensor? I think* it's key on (but engine off), accelerator pedal to floor for 20 seconds, then key off and start as normal.

* Disclaimer: I recoded my trans years ago to disable the adaptive shift logic (personal preference), so I'm going from what I'm remembering being written around the boards for this. Should be able to turn it up in a search, might be wise to ensure I don't have the process wrong.

You can monitor which gear is commanded in the TCM data.

As I stated in my first response, it sounds like you have a couple problems.

Often "low power" gets falsely blamed on the transmission, because when you have the accelerator floorboarded to get up to speed, the TCM will keep the trans in a lower gear... and if it is really down on power in may not EVER get up to sufficient speed to allow for the highest gears.

Even if the TCM was in limp mode, which is fixed 4th gear no lockup IIRC, the car could still, eventually, get up to speed.... even illegal speeds.

Rob Mayercik said:

Something still sounds off - I'm turning about 2600-2700 at 70 on the speedo.

Wonder if the "fuzzy logic" is messed up due to the sensor... did you reset the trans computer after doing the sensor? I think* it's key on (but engine off), accelerator pedal to floor for 20 seconds, then key off and start as normal.

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I drove it again, the transmission seems to have settled in a little bit. I confirmed that it is at 2600rpm at 70mph.
Thanks for the TCM reset trick, I'll look into it.

oilhammer said:

You can monitor which gear is commanded in the TCM data.

As I stated in my first response, it sounds like you have a couple problems.

Often "low power" gets falsely blamed on the transmission, because when you have the accelerator floorboarded to get up to speed, the TCM will keep the trans in a lower gear... and if it is really down on power in may not EVER get up to sufficient speed to allow for the highest gears.

Even if the TCM was in limp mode, which is fixed 4th gear no lockup IIRC, the car could still, eventually, get up to speed.... even illegal speeds.

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You can say "I think it sounds like you have a couple problems" all you want, but if that's all you say, then it's useless.

As indicated to be 'the #1 thing to do' in the thread, I replaced the G68 sensor and now I'm sifting through new issues.
I'm looking for the next hint on which direction to go in.

BTW - I did actually get it up to 80mph last night. Cruises on flat ground fine. A steep grade might cause issues though. I understand low power could be the motor, or it could be low fluid in the TC preventing power from being transferred. I'm looking for someone more experienced to chime in so that I can use what little free time I have dicking with the car as efficiently as possible.

More experienced than Oil Hammer.. hmmmm.

A friendly note, I would take the sage advice that OH has provided.

kbaisley said:

More experienced than Oil Hammer.. hmmmm.
A friendly note, I would take the sage advice that OH has provided.

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Will check vacuum lines.
Thanks

I'm done with this thread, and really growing tired of newbs with attitudes that come here asking for help, with vague incomplete information provided, only to ignore things some of us who actually work on these cars for a living provide (for FREE) and think they know better.

Here's a clue: IF YOU KNEW BETTER, YOU"D NOT HAVE STARTED THE THREAD IN THE FIRST PLACE.

Good luck, I'm out.

oilhammer said:

I'm done with this thread, and really growing tired of newbs with attitudes that come here asking for help, with vague incomplete information provided, only to ignore things some of us who actually work on these cars for a living provide (for FREE) and think they know better.
Here's a clue: IF YOU KNEW BETTER, YOU"D NOT HAVE STARTED THE THREAD IN THE FIRST PLACE.
Good luck, I'm out.

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lol k. I can tell you're pissy that someone disrespected your self-given title of "the know it all."
Let's be real here - I'm extremely knowledgable about working on cars. I'm a 4th year mechanical engineering student. Just not experienced or knowledgable about diesels or these quirky-as-hell VWs
I went out of my way to provide as much detail as possible. I literally edited and trimmed my OP for about 30 minutes because I was worried about it being TOO detailed.
I have given much, much more information than 99% of other "HALP ME PLZ" threads.
Then you come on here and say "hmm. Me think it's more than 1 issue. Maybe check vac lines"
Then a couple other people say 'G68 sensor' and you say "yeh yeh! replace G68"
So I replace the G68, then come back and ask what's next, while providing additional in-depth information.
And you post "LIKE I SAID - METHINKS YOU HAVE MORE THAN 1 ISSUE"

When I get frustrated that you're playing some weird vague "let me try to act like I'm helping but just repost a useless piece of info from before" games, you get pissy.
Thanks, you're a ton of help dude.

stomachbuzz said:

lol k. I can tell you're pissy that someone disrespected your self-given title of "the know it all."
Let's be real here - I'm extremely knowledgable about working on cars. I'm a 4th year mechanical engineering student.............................

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Oilhammer has never laid claim to anything. He got it the old fashioned way.
If he's not #1 here he is in the top 3. And he often comes with attitude.
But he always tries to help, instead of critiquing the negative just follow his recommendations and you'll be almost done.

stomachbuzz said:

...I'm a 4th year mechanical engineering student.

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And this makes you more experienced than someone with 20+ years of VW diesel expericence.

stomachbuzz said:

Just not experienced or knowledgable about diesels or these quirky-as-hell VWs

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So you have no experience but get upset when someone tells you to do the basic troubleshooting steps.

stomachbuzz said:

... I understand low power could be the motor, or it could be low fluid in the TC preventing power from being transferred.

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Serious cringe brah.

STDOUBT said:

Serious cringe brah.

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....?