V6 TDI intermittently in limp mode, workshop wants to replace the turbocharger

Hi everyone, after spending 2 hours using the search function, I still haven't been able to locate the problem! The car is an A4 V6 TDI, manufactured in 1999. The car occasionally goes into limp mode, and the recorded error code is the usual 'control difference' error. The workshop supposedly replaced the control valve, but there was no change, so the original part was put back in. I've read that the VTG (Variable Turbine Geometry) should 'move' when the ignition is turned on or the engine is started. However, in this case, absolutely NOTHING happens. My question is: It seems like the VTG is faulty (either stuck or the spring is broken). Why does the error only occur sporadically, and not all the time? Thank you in advance for your help.

Best regards, Christoph.

Hi,

I would do the following next:

Check all the vacuum hoses. If any of them are porous, the control valve may be working properly, but it won't be able to regulate anything.

If that's okay, then use a hose and a LARGE syringe (or a vacuum pump) to connect to the VTG adjusting valve, and see how it reacts to the vacuum.

If nothing moves, it's stuck. If it's moving, then the problem lies upstream, in the hoses, the valve, or its control system.

Best regards,

Jan.

Hi,
Then you either didn't search thoroughly enough, or you found so much information that you couldn't see the forest for the trees. Usually, this means that the VTG (variable turbine geometry) is mechanically jammed, which causes the boost pressure to become too high. There are many posts, and furthermore, a specialized article.

Okay, so the VTG rod definitely needs to move out of its resting position when the engine starts, right? Okay, I'll try that! Sure, here's the translation:

'Thank you in advance.'

Hi,
Okay, let's start from the very beginning and try to move the VTG manually, either by hand or by creating a vacuum manually.

What I don't understand is: The error is known. So why is a new charger simply installed instead of cleaning the old one? The workshops would earn significantly more from the cleaning service than they would from installing a new loader, and the customer would save money.

Best regards, WarLord.

What I don't understand: The error is known. Why is a new charger simply installed instead of cleaning the old one?

for the same reason that I immediately discard circuit boards with occasional failures:

- operational safety

'If I, as a workshop, verschandeln a VTG (Vehicle Tracking and Geolocation device), I cannot guarantee that it will run flawlessly for another 100,000 km. If it fails again after 5,000 km of cleaning, the customer will come back, and rightfully be very angry! And I'm stuck with the costs, because they'll grab me by the collar and demand their warranty.'

Can you definitively say WHY the VTG (variable turbine geometry) is stuck? Is it just due to the Russian components, or is the mechanism warped?

The problem with workshops is that they don't provide customers with arguments or explanations.
In my experience, 90% of customers understand why a new part needs to be installed if you explain the reasons to them and, above all, are honest with them.
'I can verschandeln it, but I can't guarantee that it will last. It might get stuck again, and then you'll need a new part. In that case, the labor costs will be wasted.' They think a lot about whether they should just get a new (replacement) part. And those who don't complain afterwards because it didn't work out. After all, I made it very clear...'

but to get back to the origin:

When does the emergency mode activate? Does it activate at full load, or when you try to apply full load? Typically, the VTG (Variable Turbine Geometry) operates in idle mode at its maximum setting, meaning it's fully adjusted. Does the emergency mode activate at full load, where it's already at its maximum setting? If so, the vacuum wouldn't be reduced.
'Does it have an emergency mode? If you demand power from it, it's probably stuck in the minimum power state.'
Therefore, it's crucial to check ALL the hoses, and especially the connections for the air mass meter (ATM) and the hose connecting it to the air filter housing, to ensure they are not blocked. Also, check for leaks, as these parts tend to become brittle and break down over time.
'When the loader is cold, you can sometimes adjust the VTG (Variable Torque Geometry) manually. It should feel heavy due to the spring, but move smoothly. Once you've checked the range of motion, the next step is the spray test, as mentioned before.'

CU Gremlin.

Okay, this is absolutely ridiculous. I have to post about this! The car was at the workshop because the 'emergency program' error kept occurring, about once a week (every 200 km). They replaced the turbocharger pressure control valve and discovered that the error immediately reappeared... so, they decided to replace the turbocharger because it was supposedly the only remaining cause. The real issue is that at the workshop, they swapped the two thicker hoses connected to the turbocharger pressure control valve, which immediately caused the error to reappear (which is strange, considering the error was very rare before, but whatever). So, they put the old control valve back in, of course, incorrectly. (so with the hoses swapped). The car, since it came out of the workshop, hasn't been running properly at all. I've now swapped the hoses back, and it's running again, but the problem will probably return, probably weekly . But now we can narrow it down more precisely! I'm currently looking for a new workshop in the area of Blieskastel/Homburg/St.Ingbert.

Hi,

Go to the workshop, get your money back (due to the mechanic's obvious lack of expertise), and then try replacing the control valve yourself (ideally, borrow one from them to test it).

A valve defect is now, once again, within the realm of possibility.

Best regards,

Jan.

Quote:

I now need a new workshop in the area of Blieskastel/Homburg/St.Ingbert.

Hi Master.

Were you at the Großklos? In HOM ???

If so - then you've learned something now (I already knew it).

After a serious conversation, my dealer (at least towards me) is very cooperative.
Background: They had performed an inspection on my girlfriend's Polo that was not convincing (they had to search for the car on the lot, it wasn't washed - for 300 euros!!, the oil was changed after 7000 km even though it wasn't necessary, etc.). One day later, I returned the car with a list of defects and received it back a day later, perfectly fixed. The inspection of my Golf went perfectly from the start .

If the driving isn't too much for you...?

Or you could come by my place, and we can use VAGCOM to see exactly what the VTG is doing.

Greetings.
m;

Do you mean the N75 valve (i.e., the one that's the same as the one for the EGR system) or the VTG unit itself when you say "VENTIL"?

m;

Hi,

Okay, when I said "control valve," I meant the N75 valve, which is similar to the control valve for the EGR system.

Best regards,

Jan.

I thought the N75 component from VTG was exactly the same part as the AGR component.

Therefore, a simple test can be performed by simply SWAPPING the valves.

I can still take a look.

Hi,

A while ago, someone posted that the two parts are similar, but not identical. The function is naturally the same, so it should be safe to swap them for testing purposes. However, I would expect that the behavior might be different (due to different dimensions, different weight of the iron core, etc.).

Best regards,

Jan.

I was at Auto Thönes here in Blieskastel... well, never mind, I'll try to figure it all out myself!

I have one more question... The error hasn't reappeared yet. Why could the control valve be broken if the error isn't occurring constantly? I actually think it's more likely that the pressure sensor might be 'worn out,' causing the control valve to exceed 100% occasionally, especially if conditions favor increased boost pressure (like cold air). Could it be that the rod simply needs to be slightly adjusted? The vehicle has 190,000 kilometers (or miles) on it.

The control valve will never exceed 100%.

Purely theoretically, it might be possible, but that's where the emergency mode comes in – when the Electronic Control Unit (ECU) can no longer control the system based on its physical limitations.

We had a thread here recently where a faulty valve was identified based on the valve's log data (because the EDC had started making "wild" control attempts).
While it was a 1Z, which is a wastegate, it can also work with a VTG turbocharger in principle.

Do you have the ability to read data yourself or log it?

m;