A4 AFB Engine Problems: Common Issues & Fixes

Hello there...

First of all, a huge compliment to the designer of this website and the forum participants. It's very clear, informative, and above all, of an extremely high quality! I immediately sent the link to a workshop, and they were also very impressed: Keep up the great work!

To my 'unqualified' problems .
I own an A4 Avant 2.5 TDI Quattro.
- MKB: AFB
- 167,000 kilometers of telecommunications network.
- Very low oil consumption (service intervals are sufficient).
- Normal fuel consumption.
- Minimal soot formation.
- New LMM.
- Most likely, the solenoid valve for the VTG (Variable Torque Generator) is defective, as I was recently in emergency mode, but the VTG and its associated components appear to be in good condition.
- There were no other errors in the error memory except for 'intake manifold pressure difference exceeded.'

After a cold start, the engine exhibits fluctuating idle speed (oscillating between approximately 760 and 900 RPM, as if someone is constantly tapping the accelerator), and it occasionally runs rough. Once the engine is warm, the idle is relatively stable, except for occasional, slight 'shaking' that is not visible on the tachometer (it might be so subtle that you can barely hear it, but I thought I'd mention it...).

With a warm engine, a significant 'torque loss' becomes noticeable in the lower RPM range: The car doesn't pull as expected from low speeds. Under heavier load (e.g., going uphill in the parking garage in 2nd gear at 1000 RPM), it even starts to jerk. During strong acceleration, it occasionally exhibits slight hesitations (jerks) around 3000 RPM. On the highway, it reaches 220 km/h downhill with a tailwind and a longing for home.
-> NHG? (I haven't performed the tapping test yet, as I haven't found any injectors with cables so far...?! Which one would that be?)

I've spent all the evenings searching this forum for information on these symptoms, but I haven't found anything. Does anyone have any ideas?

Here's something to keep in mind: Since I don't know anyone who has a VAG-COM, I would have to go to the dealership to have the data read out and bring the printout with me. Do they do that? Or perhaps someone from the forum would be willing to help me out with their VAG-COM in the HH area (in that case, please send me an email - of course, this will be compensated. )?

Thank you very much in advance.
Cara.

Hello,

Thank you for your kind words!

Unfortunately, I am not a V6 specialist myself.
Using the search function, I found the following information in the error database:
/viewtopic.php?t=131&highlight=afb

Best regards, Rainer.

Hello Rainer,

Not only competent, but also incredibly fast, right?

I've also already looked at the description in the error database. I was just hoping there might be a less expensive way to initially make a more or less certain diagnosis. I didn't want to have half a timing belt replaced just based on a suspicion. Is there perhaps another way to read or determine if the valve timing is misaligned?

Is it advisable to replace the timing belt at the same time as the repair described in the article? Mine is only '50,000 km' old and wouldn't be due for replacement for another '70,000 km,' but such a significant additional cost shouldn't be too much, right?

Regards,
Cara.

Hello,

Well, as suggested, disassembling and testing the tensioner is indeed a time-consuming process.
Just check the tension of the timing belt, at least with a very loose belt, you should definitely notice something.

Best regards, Rainer.

If this is the cause, error code 0550 (start of injection, control difference) should normally be stored in the engine control unit's error memory.
However, another problem is known with the V6 TDI engines. Due to the combination of unfavorable tolerances, it can happen that, after approximately 150,000 km, wear marks on the camshaft lobes can lead to altered valve opening angles. The consequences are almost exactly as you described. I would tend to lean more in that direction.

However, another problem is known with the V6 TDI engines. Due to the combination of unfavorable tolerances, it can happen that, after approximately 150,000 km, wear marks on the camshafts can lead to altered valve opening angles. The consequences are almost exactly as you described. I would tend to lean more in that direction.
That would be a bitter pill . I just found the relevant entry in the error database.
I'll probably make an appointment with Audi and see if they can do anything for me free of charge, although I don't really expect much given the mileage and age (first registered in October 1998).

If I have any results, I will definitely post them here.

Thank you very much.
Cara.

Hi,
If the head cover on the V6 TDI doesn't go down significantly further than on the R4 (no... not the old Frenchman }), I would recommend taking a closer look at it before visiting a dealer.

Best regards, Rudi.

Hi Rudi,

As I tried to explain in my initial post, I'm not very familiar with working on the engine. I did buy the 'How it's done - Audi A4' book when I bought the car, but unfortunately, it doesn't cover the V6 TDIs at all. In my opinion, the book was a complete waste of money because it hardly mentions the specific features of the Avant models .
Since my last cylinder head cover came from a very old gasoline-powered Polo, I'm not really keen on testing my luck right before a potential partial goodwill repair (even though I'm very interested).

I think I become much 'bolder' when there's no more expectation of leniency.

So long, and still thank you for the tip }.
Hi Cara,

I'll probably make an appointment with Audi and see if they can do anything for me free of charge, although I don't really expect much given the mileage and age (first registered in October 1998).


Hi!

I also had an engine failure with my car (manufactured in May 1999) exactly one year ago.
It gradually got slower and slower within half a year... and then, suddenly, it stopped. The camshafts looked terrible... as if someone had used a cutting disc on them. In the workshop, they always said 'it's the mass airflow sensor,' but after the third replacement (under warranty), it finally came to this.

I received a new engine block free of charge, even though the car has 140,000 km on the odometer.
--- after days of writing letters and sending faxes... ---

Unfortunately, they didn't replace the blower fan back then... About 3 months ago, the fan broke, and it pretty much shredded the entire internal components. Luckily, the warranty covered it... I didn't want to deal with any more issues under goodwill.

P.S. By the way, the LMM has failed again... I think this is the fourth time now.

Regards,
Felix.

Hello!

The problem is solved!!! It purrs and runs like a sewing machine .

The entire problem was caused solely by the solenoid valve for the VTG (Variable Turbine Geometry). The low mass airflow (LMM) values provided a clue, but they didn't change even after replacing the valve with a new one. Since the VTG itself was operating smoothly, the problem was narrowed down to either the sensor or the valve itself, which was then confirmed through testing.

Just to be on the safe side, I still checked the timing belt tension and the camshafts, but everything looked very good.

I suspect that the solenoid valve only experienced very short interruptions during the 'high-frequency' switching process for lower pressures. If it were completely defective, this would have been detected during the visual inspection of the VTG adjustment or, at the latest, in the error memory (please correct me if I am wrong).

I still don't understand what the sawing/nailing sound had to do with it (which, by the way, has now disappeared). Can someone perhaps shed some light on that for me? Also, I didn't expect the turbo to be so noticeable even at such low RPMs...

P.S. By the way, the mass airflow sensor has failed again... I think this is the fourth time now...
Okay, I've now received the fifth one. Have you already deactivated/had deactivated the 'burn-in' function for the mass airflow sensor (MAF)? This should significantly reduce the MAF's 'consumption' of fuel. My Audi dealer even did it as a goodwill gesture. I'm not sure yet if it will actually make a difference, as it was only done recently...

Thank you again to everyone .
Regards, Caramon.

Hello Caramon,

I'm afraid we will hear from you again sooner or later.

If the timing and belt tensions are correct, that's already a good start.

You might just have an electrical problem... time will tell.

Best regards, Rainer.

P.S. By the way, the mass airflow sensor has failed again... I think this is the fourth time now...
Okay, I've now received the fifth one. Have you already deactivated/had deactivated the 'burn-in' function for the mass airflow sensor (MAF)? This should significantly reduce the 'consumption' of the air filter box (AFB). My Audi dealer even did it as a goodwill gesture. However, I'm not yet sure if it will actually make a difference, as it was only done recently...


How do you do that? And what is that?

Regards,
Felix.

Hello Felix,

Look at this: /viewtopic.php?t=1266&highlight=v6+luftmassenmesser

Best regards, Rainer.