Audi A6 Avant TDI: Intermittent Power Loss, 192k Miles

Hello everyone,

So, I'm a complete newbie here, but first of all, a huge compliment to the 'creators' of the forum!

I've always driven diesel cars, and now I'm switching from an A4 1.9 TDI with 110 horsepower to a...
A6 Avant, manufactured in 1995, 2.5 TDI, 150 horsepower, quattro, has been replaced.
It's a great car, but I already experienced problems after just the first 30 minutes of driving after buying it.
It was observed that the car occasionally experienced a loss of power.

The coolant overflowed even though the gauge indicated 90°C.
2. While going downhill in second gear, the speed was 30 km/h with no acceleration.
3. Then, accelerate fully again.

So far, we have checked:
* Nothing was detected by the diagnostic device.
* Afterwards, the mass airflow sensor (MAF sensor) was replaced.
--> no success.
* Afterwards, the fuel injection pump was replaced.
--> no success.
* On Monday, July 26th, the fuel injectors will still be replaced.
* The fuel tank has been removed and cleaned, and the diesel filter may have been replaced.

and then the mechanics don't know what to do anymore...

Has anyone else ever experienced the same problem?
Please help me; the car is actually in excellent condition, and then something like this happens...

Note: The performance degradation occurs intermittently.

I've also considered that perhaps a sensor is faulty or that the engine control unit has a loose connection (although this should be detected by the diagnostic tool!).

Thank you, and I hope to receive many responses and help.

Best regards, A6AVANTfan.

Quote:

(but should be recognized by the diagnostic device?!)

Not necessarily.
I once had a loose connection on the MAF sensor connector. It didn't throw any error codes, but it caused the airflow to be limited to 0 mg/stroke !!! The car felt completely sluggish.

We only found it during a test drive with a VAGCOM connected.

Log everything possible and keep driving until an error occurs.

Or you can continue with this (somewhat hasty, in my opinion) exchange frenzy... But it's going to get expensive quickly...

m;

Hello Dieselmartin,

Thank you for the quick help. However, I don't think it's 'rushed.' I just bought the car and drove it for 30 minutes, and now it's back at the dealership where I bought it. They've taken it to an Audi workshop.

The mechanics there are a bit clueless and immediately started replacing parts.
(after testing with VAG-COM)
This parts exchange doesn't cost me anything, and I have a 12-month warranty, but right now I'm worried that they won't be able to find the fault, and I'll be left without a solution.

My brother, who is also named Martin, is a mechanic, and we just discussed what the problem might be.
Because if they really can't find the problem, I believe you'll find more advice and solutions from specialists and hobby mechanics here than you would in a workshop with people who have little experience with specifically 5-cylinder A6 cars.

So, you mean that the LMM might have a loose connection? *Hmm*, that sounds plausible to me.
It's been replaced before, and it turns out the problem is just the connector.

The strange thing is that the car doesn't stall or hesitate at a specific RPM, but rather it happens sporadically, whenever it feels like it.
After replacing the fuel injection pump, the mechanics drove for 45 minutes, and then, on the way back, the sudden loss of power occurred again. They were traveling at 160 km/h on the highway when suddenly the engine made a 'ooohmmm' sound, and then it regained full acceleration, regardless of the gear.

I'm going to suggest they use VCDS during the test drive.

By the way, it's also possible to do this with a regular laptop, and you can make your own cables, right? (I read that somewhere.)

Hi,
I suspect your A6 is a 5-cylinder engine with 140 horsepower, so it's likely an AEL model.
"Intermittent power loss is also known as limp mode. In this vehicle or control unit, the limp mode is deactivated when the engine reaches idle speed."
"I once had a similar issue with my car, where there were no error codes stored. A hose that runs from the turbocharger intercooler connection pipe to the boost pressure sensor had gotten caught on the EGR valve due to a broken cable tie and was melting. This immediately triggered a limp mode. The end of the hose then melted to the hot valve, and the car ran somewhat normally after that..."
Tip: Remove the upper engine cover and check all the hoses and their routing.

Regards,

Olli.

Yes, it's an AEL with 140 horsepower, and quattro, of course.

That sounds like an interesting solution.
The funny thing is that the car stood in the same spot for about 3-4 months without anyone driving it.
According to the previous owner, the water pump was only replaced at 180,000 km, and that was all the maintenance that was done.

Could it be that, when I check the cables, I might find that a badger or something similar has chewed through one?

I don't understand the connection between that and the overheating. Maybe the sensor is faulty?

Hello everyone,

Thank you again for your help.

The problem has now been identified, and it was definitely not the mass airflow sensor or the cable.

Guess what: It was the turbocharger valve that was broken.

Now, put in a new one, and the A6 will run like new again.

Thank you again.

A6AVANTfan wrote:

Guess what: It was the turbocharger valve that was broken.

I'm being really picky today: That car doesn't have that. You probably mean the wastegate, but that's not actually a valve, and it can't be replaced separately, at least not by just any mechanic.
It's good that you're letting me know even after the issue is resolved, but I'm also curious about what actually caused it.

I think that A6Avant was referring to the pressure sensor of the turbocharger...

Hello.

Well, that turbo thing wasn't as easy as it seemed...

While the strut was stuck, the turbo wasn't the problem.

Today I picked up the car, and it's not working again.
The workshop doesn't want to take the car anymore because they don't know what else they can do.

In the meantime, I'm also not sure what else I can do or organize.

Can I contact Audi directly in Ingolstadt, or in Austria, the headquarters in Salzburg, even if I am a private individual?

Thank you again for your suggestions and assistance.

Hi, take a look at this:
/viewtopic.php?t=5088&highlight=

It seems I had a similar problem. Since I opened the engine control unit and installed a tuning chip, the effect of the power loss/shutdown has disappeared.

Previously, the VAG group also made silly and foolish mistakes, failing to identify the problem.