VW Catalytic Converter Test: Is it Working?

Hello.

Our VW Sharan (manufactured in 2011, 200,000 km, vehicle type: 7N-VW36 (7N0)) has repeatedly shown the error code "P0299 00 [096] - Control limit not reached" at the garage.

It all started with the exchange of the AGR (Confidence-Building Measure).

First, the vacuum pump in the garage was replaced, but it didn't work.
Then it was said that the DPF is clogged.
(This unit had been cleaned six months ago or after 20,000 km.) So, we sent it back to the cleaning company so they could re-check the cleaning process. The DPF is in good condition; after another cleaning, 7 grams of ash were removed.

Now, the catalytic converter is supposedly defective. Based on what I've read here, that could be the cause.
Therefore, my question is: is there a way to test this?

I have performed several drives and logged various values using VCDS.

The boost pressure deviates from the target value by more than 500 mbar.
The differential pressure above the DPF also reaches 950 mbar.

What I don't understand is why the differential pressure is so high. If the exhaust gases are backing up behind the DPF, then they must also be backing up in front of the DPF.

The idea is to use the differential pressure sensor (which has also been replaced) by leaving one side open, thus measuring the pressure before and after the DPF.

Thank you in advance for your help.
René.

Hello,

Unfortunately, your logs make the statement seem plausible. To be sure, you should monitor the differential pressure at the DPF (Diesel Particulate Filter, which is the catalytic converter) when driving at full throttle. Here you can find reference values:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

If the differential pressure at the DPF is also noticeably high and regeneration of the DPF is not possible, it is likely that the DPF is "clogged."

Please check first the VTG control of your turbocharger (check the actuator/control element, possibly with a vacuum hose test), so that it's not simply the reason why no boost pressure can be built up, and the DPF (catalytic converter) is damaged in the long run. Even a damaged vacuum hose can cause this.

Best regards, Rainer.

Okay, I just watched your third log, and the DPF (catalytic converter) is clogged. It needs to be removed and either sent to a specialized cleaning company or replaced.
The engine can no longer regenerate it.

Please also check the vacuum hose connection for the VTG (Variable Turbine Geometry).

How long has the vehicle been running in emergency mode? Unfortunately, the DPF damage may have been caused by a faulty vacuum hose because the driver simply continued driving.

Here's a tip for readers: With HEX-NET, you can even check what's happening while you're on vacation, for example, using your phone, and then have the "emergency program" here assess the severity of the situation.
A misaligned clutch switch almost ruined my vacation, but luckily I had my HEX-NET with me to identify the harmless nature of the error.
Without HEX-NET, I could have driven to the nearest workshop in Italy, but would it have been enough time to make it to the ferry?

Best regards, Rainer.

Hello Rainer,

Thank you for the response.

How did you recognize that so quickly?

Regards,
René.

"Due to the extremely high differential pressure across the DPF, exceeding 900 mbar, and the very high "soot load." This soot load is calculated, meaning that the extreme differential pressure has been present for some time."

Best regards, Rainer.

Hello Rainer,

Yes, the differential pressure is very high. But how can I even measure it?
If a blockage occurs in the DPF, then there should also be a blockage before the DPF, which would mean the pressure difference would be minimal.

And is it definitely the catalytic converter, or could it also be the rear muffler, or something else in between? And can I test it somehow using VCDS?

Thank you and best regards.
René.

Hi, the DPF is the catalytic converter.

dieselschrauber wrote:

Hi, the DPF is the catalytic converter.

Certainly, that's the case with your car. It's the same component, and it has multiple functions.

May I ask how the current error situation arose?
That didn't just happen on its own; it had a cause.
This can be something as simple as a stubborn issue with an unsuitable driving profile or a faulty sensor, or it can be more serious, such as a defective turbocharger with high oil consumption.

Anyway, the cause should be clarified, otherwise you won't enjoy the vehicle for long, even with a new/cleaned DPF.

Best regards, Rainer.

Hello Rainer,

Okay, that's a misunderstanding.

I've just noticed that the DPF is also labeled as being connected to the catalytic converter.

[...Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.

I meant number 4 (7N0 254 400 NX - catalytic converter).

For me, item number 1 is the DPF (7N0 253 053 BX - exhaust pipe with catalytic converter and particulate filter).

Back to your question.

As I mentioned, it all started with the AGR.
After the error appeared, we drove another approximately 2000 kilometers because the workshop didn't have an available appointment to fix it immediately.
Even then, the car repeatedly tried to regenerate the DPF (after the engine was turned off, the fan ran for a longer period).

Just under a week after replacing the AGR valve (on Saturday), I was on the highway and, while accelerating on a hill, the error message "P0299 00 [096] - Control limit exceeded" appeared.

So, back to the garage. They tested the vacuum system for leaks for a short time (about 30 minutes). The result was negative - everything seemed to be sealed.

Unfortunately, there were no available appointments, so I had to wait four weeks to get a time slot for troubleshooting, and I drove approximately 1000 km in the meantime.

After approximately 1 day of troubleshooting, the vacuum pump was replaced. The result was that the DPF was not regenerating or the regeneration process was being interrupted.

Then, we spent 2 days troubleshooting, with the DPF being regenerated multiple times at the request of the workshop, but without success.
(Meanwhile, the car was only running in emergency mode because the regeneration process could not be completed.)

Then it should be the DPF (defective, with melted ceramic material). So, it was removed and sent back to the cleaning company (under warranty). The result: the DPF was fine, no defect. It was cleaned and tested again - 7 grams of ash were removed (after 20,000 km).

DPF installed. The error "P0299 00 [096] - Limit undershot" is still present.
Differenzdrucksensor getauscht, verschiedene andere Sensoren aus anderem Fahrzeug quergetauscht. Without success.

CAT was installed from another vehicle, and it was supposed to be working properly afterward. The garage did a short test drive, but not on the highway.
Therefore, it should now be the KAT system. (Cost: 2000 CHF)

Since the garage wouldn't guarantee the accuracy of their diagnosis (I don't want to invest 2000 CHF and then it turns out to be something else, like with the DPF), I picked up the car again (with the old catalytic converter) and now I'm doing a test drive with the HEX-V2 that I bought from you in the meantime.

I hope you can follow the process.

"If it's the catalytic converter, then that's fine with me. However, after being diagnosed with a 'defective DPF,' I don't want to just replace the catalytic converter based on suspicion, only to find out that it's something else, like the muffler."

Thank you for your help.

Best regards.
René.

Hello René,

Please do not include links to illegal websites, otherwise I may have to pass on any resulting costs to you.
This is not something that vehicle manufacturers appreciate, and it is pursued with varying degrees of intensity depending on the country.

The VW illustrations in the parts catalog are merely schematic and do NOT necessarily correspond to the actual installed configuration.

Whether the SCR unit is integrated into the catalytic converter/DPF or located separately, the same principle applies. The differential pressure is measured across the entire system.

I always recommend including pictures of the specific vehicle, as this clearly shows how the part is actually installed.

As you describe it, the underlying cause is a DPF regeneration problem. If you hadn't continued driving, you could have avoided the time-consuming and expensive removal/replacement of parts of the exhaust system.

The following can help determine why the DPF is not regenerating:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

If the high back pressure was truly only caused by the rear silencer, it would have been possible to remove it and take a test drive – the DPF, catalytic converter, and SCR unit would still have been functioning normally. You should only test again after replacing or cleaning those components.

If the DPF is not regenerating, you can use VCDS to find out why. This can help you avoid expensive follow-up costs. Your bad luck was simply waiting too long.

Best regards, Rainer.