TPS Issues

[BeetleDragon737]

Hi all. I have a 1999.0 New Beetle. I'm having some troubles with my TPS or electrical connections related to it. I know this is a common problem, but it seems to be one that is very difficult to diagnose.

From what I've read, the issue could stem from a bad ECU, a bad TPS/pedal, or any one of a number of bad electrical connections. I've taken my car to a knowledgeable shop, and they spent a while checking out the voltages and resistances related to the TPS and such, and they said everything looked good. The only issue was some serious corrosion around the grounds at the ECU, which they cleaned. I drove the car for another 40 miles, and then the accelerator died again.

I'm on the verge of replacing my TPS and/or my ECU, but I don't want to spend $1200+ when that won't necessarily fix my problem. I also would like to get a tune, but I don't want to tune my ECU if it's what is causing the problem.

A few questions:

• 
  After you all have heard about this issue again and again, what seems to be the most reliable way the problem gets fixed?

• 
  Are there any differences between an ECU issue and a TPS issue that I would be able to notice as I'm driving and the pedal gives out?

• 
  And are there any electrical connections that are easily accessible that I could visually inspect for corrosion, etc, that wouldn't require electrical engineering expertise to fix up?

 

[Mako]

If you have cruise control, use it and the pedal is bypassed. See if your problem persists.

 

[BeetleDragon737]

Yes, when the issue happens, I can use cruise control to accelerate myself to highway speeds. I don't think that helps me diagnose the source of the problem though. Once it happens for a split second, the car will immediately disable the go pedal until the car is turned off, and this would happen whether the problem originated at the ECU or at the pedal, right?

 

[Mako]

If cruise works the problem is not ECU to IP or power / earth to ECU so confine your fault finding to pedal and wiring to ECU. Fault codes?.

 

[BeetleDragon737]

The only fault code that showed up was 018047, which isn't actually a code that makes sense. It should have been 18047.

So if it was the ECU, when it cuts off the function of the accelerator, it would do that for both the cruise and the pedal?

 

[FlyTDI Guy]

I might mention that $1200 is way too high.

http://shopping.boraparts.com/product_info.php?products_id=1142

For the ECU (if needed) I'd be looking for a used one here...

www.car-parts.com

I picked one up years ago using them and paid around $100...

Either can be installed with minimal tools/knowledge and a little help from Fred's as needed.

 

[BeetleDragon737]

$200 is what I was told for the pedal at the shop, but they were quoting much higher for the ECU. They were giving me rough numbers, but both the labor and part were pretty pricey. They mentioned that they would have to re-program a used ECU before putting it in my car.

Should I be able to plug in an ECU from a beetle, same year, and it would work fine without any extra effort?

Edit: Also, on the car-parts site, is the ECU referred to as the "Engine Computer"?

 

[FlyTDI Guy]

$200 is what I was told for the pedal at the shop, but they were quoting much higher for the ECU. They were giving me rough numbers, but both the labor and part were pretty pricey. They mentioned that they would have to re-program a used ECU before putting it in my car.

Should I be able to plug in an ECU from a beetle, same year, and it would work fine without any extra effort?

Edit: Also, on the car-parts site, is the ECU referred to as the "Engine Computer"?

Engine Computer is correct. Yes, it would involve a little Vag-COM work to introduce a different ECU to your car. From the sounds of it, given a good signal the computer can set fueling properly as evidenced by your CC working. I'd be suspecting the TPS or wiring to it. Be interesting to know exactly how they tested your TPS. They don't fail often but it's not unheard of.

 

[BeetleDragon737]

Correct me if I'm wrong, but if the ECU receives a bad signal, or thinks it receives a bad signal, from the TPS, won't it just cut the signal from the pedal until the car is turned off? Then the cruise control would still work fine continuously even though the pedal doesn't work.

Or is the cruise control on the same circuit as the pedal, so that if the signal from the pedal is cut off, the signal from the cruise control will also be cut off? But if that's the case, then wouldn't the cruise control stop working whether it was the ECU or the TPS?

Sorry for being difficult, but I don't see how the CC working affects the diagnosis...

 

[BobnOH]

I thought the code stuff seemed relavant

 

[FlyTDI Guy]

Correct me if I'm wrong, but if the ECU receives a bad signal, or thinks it receives a bad signal, from the TPS, won't it just cut the signal from the pedal until the car is turned off? Then the cruise control would still work fine continuously even though the pedal doesn't work.

Or is the cruise control on the same circuit as the pedal, so that if the signal from the pedal is cut off, the signal from the cruise control will also be cut off? But if that's the case, then wouldn't the cruise control stop working whether it was the ECU or the TPS?

Sorry for being difficult, but I don't see how the CC working affects the diagnosis...

Lacking a plausible signal from the TPS, the ECU should default to 1100 rpms and allow you to idle your way home. There is a potential catch-22 going on here though. If the cruise control works, it would seem you would need a plausible TPS signal for the ECU to allow CC to work. I know it doesn't work if your clutch pedal or brake switch go bad. If you wanted to manually accelerate while CC was active (other than the stalk button) you'd want the TPS input to override the current speed setting. If that signal were wonked, seems like the ECU would lock out CC. Just speculating... any actual experience is welcome.

Also, a TPS issue would set a code and should be fairly easily diagnosed using VCDS/Vag-COM. Not sure what your shop is using but VCDS gives fairly specific indicators to locate the problem.

 

[BeetleDragon737]

VCDS gave this when they scanned the car:

1 Fault Found:
018047 - Unknown Error Code

C067F - 35-10 - -​

Readiness: 1 1 0 0 0

The shop said that 018047 is not a code, and the zero shouldn't have been there. He said that because the zero was stuck on there, there's a chance it's the ECU that's going wonky, but he didn't say more than that. So the code really is 18047, which is the typically cryptic "Accelerator Position Sensor - Implausible Signal". Nothing else came up.

I thought the code stuff seemed relavant

Hmm, so it could be the oxygen sensor (MAF?). I don't recall the shop mentioning anything about that.

 

[BeetleDragon737]

Just as an update for anyone interested:

TDIs don't have an oxygen sensor. That's only gas cars (the reason it's an issue is because the insulation on the wires going to the oxygen sensor is sometimes damaged due to proximity to the exhaust or from dragging on the ground).

I have now replaced my accelerator pedal. Hopefully it won't happen again.

 

[CopaMundial]

TDIs (2003 or earlier in North America) don't have an oxygen sensor.

Slight correction in red highlight