A6 3.0 TDI Commonrail: Low fuel pressure

My A6 with engine code CDYC is giving me some trouble right now. I am currently in Croatia with my campervan, and I am now experiencing the following problem:
Sudden and persistent loss of power accompanied by flickering of the filament.
The engine control unit (ECU) is displaying the error message "fuel rail pressure too low, intermittent."
The peculiar thing is that, after the car has been standing for a while, it runs normally for about 5-10 km before the problem reappears. I had the fuel filter replaced at a VW workshop.
(There isn't much information about Audi here.) After that, the car ran for about 100 km without any issues. Currently, I'm near Rijeka, and today I spent the entire day at the Audi workshop in Rijeka, where I was completely ripped off. They cleared the error codes for 190 Kuna (approximately 26€), with the comment that the error might reappear. They said that since the error wasn't present at that moment, there was nothing else they could do. I already said that.
What other self-help options are available to me? Of course, I have VCDS with me.
The engine starts normally, both when it's cold and when it's warm.

I hope you can help me.

Best regards,
Benno.

Hello,

Was the replaced diesel filter examined for debris/dirt? Next time, I'll chop it up...
Affordable alternatives would also include pressure regulating valves or pressure sensors.

Best regards, Rainer.

Hi,
You have VCDS with you. It's likely that CDYC no longer uses measurement blocks, but rather extended measurement values. Within those, you should find the values relevant to rail pressure (engine speed, target rail pressure, actual rail pressure, control module data, etc.). You can save your selection.
And that's how you log in.
Also, the car probably has a mobility guarantee, or even still has a warranty. I would also suggest calling or emailing Audi directly.
hg
Herbert.

I have just compared the actual output with the desired output. The pressure reading fluctuates wildly, sometimes above the target value and sometimes below.

@ Herbert - unfortunately, the warranty is no longer valid. The car is from December 2008 and has 217,000 kilometers on the odometer.
Is the pressure regulating valve located on the high-pressure pump, where the connector is plugged in?
Please excuse the silly question - I'm familiar with traditional diesel technology, I learned about it a long time ago, but common rail technology is completely new to me. And because it had always worked before, I hadn't really looked into it further.

Best regards,
Benno.

"One more question: Is it possible to replace the pressure regulating valve without removing the pump?" In what price range does such a valve fall?

Quote:

One more question: Is it possible to replace the pressure regulating valve without removing the pump? In which price range does such a valve fall?

Yes, it should be secured with 3 Torx screws (M6) and can be pulled out after loosening the screws (due to radial sealing O-rings).

As far as I remember, it costs around €100 (net, purchase price) at Bosch, while with VW/Audi, you'll only get the entire high-pressure pump.

Thank you for the response.
I have an appointment with the Bosch service on Monday, I'll let you know how it goes.

Best regards,
Benno.

For a 4-cylinder engine, there are two valves for pressure regulation and one sensor.
- Fuel pressure control valve N276, located on the fuel rail on the return side;
- Fuel metering valve, N290, located on the pump.
- Fuel pressure sensor G247, located on the fuel rail, on the pump side;
It should be similar for the V6 engine as well.
hg
Herbert.

PS: The two manifolds are connected by a pipe.

Hello, and thank you very much for your help.

I once took a picture of the two components connected to the overhead line.
The first image shows the right-hand rail with an actuator at the end of the rail. The visible tubes are return lines.

The second image shows the left rail, where nothing else is attached except for what appears to be a temperature sensor. Additionally, there is a pressure line connected to the other rail. Both rails have their own connection to the pump.
I think that the part on the right rail is the control valve. Is this a Bosch part?
Best regards,

Benno.

Hello,

I have named the images; they are labeled "Fuel pressure control valve N276" and "Fuel pressure sensor G247".

Best regards, Rainer.

Hello,
"I was at the workshop yesterday. The Bosch service here is a bit different from what we have. It's a MAN truck workshop with an attached passenger car department that works closely with Bosch." The employees are very competent, however.

My car was connected to a diagnostic tool, and after a brief examination, I was told that the common rail pressure sensor was likely the culprit. The part has been ordered and is scheduled to be installed on Thursday.

The statement about the pressure sensor aligns with my information.
My son contacted an acquaintance who works at an Audi repair shop. According to the repair manual, if there are pressure fluctuations in the fuel rail, the pressure sensor should be replaced. The issue, particularly in engines with high mileage, is the minimal wear that accumulates in the rail and ends up in front of the sensor, leading to inaccurate readings.
I hope the haunting is over then.

Best regards,

Benno.

Quote:

My car was connected to the diagnostic tool, and after a brief examination, I was told that the common rail pressure sensor is likely the culprit.

It would be great if that were the case (the most cost-effective solution), and I'm rooting for you!

Hello,

Unfortunately, that wasn't the solution. The car is now, regrettably, at Porsche Rijeka. I will report.

Best regards,
Benno.

Quote:

I had the fuel filter replaced at a VW workshop. Okay, please provide the German text you would like me to translate. I will then provide the English translation. After that, the car ran for approximately 100 km without any issues.

From this, one could infer that there is some diesel fuel in the tank that is clogging the filter and causing the pre-injection pressure at the inlet of the high-pressure pump to drop. This can lead to a rail pressure that is too low.
Okay, let's check what's inside and replace the filter again. And check what's inside the old one.
The fuel pressure regulation might also be malfunctioning. What values do you get when the engine is starting, idling, and under load? Are the cables and connectors in good condition?

However, the error symptoms, combined with the mileage, unfortunately suggest a damage to the high-pressure pump. That's why we asked about the presence of metal shavings in the fuel filter earlier. VW/Audi anticipates a complete replacement of the fuel system, with costs in the five-figure range.
The scope is debatable.
Do you have a letter of guarantee for the return transport of the car and trailer?
hg
Herbert.

Hello,

After consulting with Audi Germany, the pressure control valve was cleaned and inspected for debris at the workshop. However, no debris was found. After two test drives totaling approximately 100 km, I was able to pick up the car. Price: €140.
After 150 km, the same error occurred again, until the next break. After that, the engine ran normally. The error occurred once more until the next stop at the Austrian-Italian border (where I bought a vignette). The remaining 1300 km were completed without any issues. I am now back home. But the fear comes along for the ride.
I've also had the idea about the dirt in the tank, but isn't the pre-injection pressure measured after the filter, before the high-pressure pump? In my case, there's definitely a sensor in the line there. I've noticed that when I have to stop due to traffic, there's a clicking sound coming from under the dashboard (presumably a relay?). Is this normal?

Best regards,

Benno.

Hi,

It sounds like you might have put "diesel soup" in the tank. You refueled again recently, and it's running again, more or less. I recommend replacing the fuel filter again and cleaning the fuel tank and the fuel pre-pump.

What does your RLF (Regler- und Leistungseinheit - Controller and Performance Unit) say about the sensor on the supply line?

hg
Herbert.