VAGCOM: Catalytic Converter Error Codes & Diagnosis

Hello everyone.

The story of ZiagL.

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.

This led me to the question of how to detect a clogged exhaust using VAGCOM.
I didn't think about this possibility of performance loss when I was writing the troubleshooting article .

Questions for the mechanical engineering experts:
If the exhaust flow is restricted, meaning there's excessive back pressure, then, in my opinion, the total mass flow of gas through the engine should be reduced .
In the measurement readings, this should manifest as a too-small mass airflow sensor (MAF) signal despite largely normal full-throttle boost pressure - essentially the classic symptomology for MAF sensor defects .

Could one then, for the purpose of narrowing down the source of the error, try installing a known good lambda sensor (LMM) as a test? And if the readings don't improve with that, should one check the catalytic converter ?

Or are there other symptoms or readings that directly indicate a blocked exhaust system?

Hi,
I would answer that question in the style of "Radio Yerevan": In principle, yes.
I'm just not sure how much a catheter can become blocked and what kind of back pressure that would create.
However, one should not only consider the mass flow rate but also the control of the bypass or the variable geometry turbine (VGT).
The increased back pressure will reduce the speed of the turbocharger, which means that the control system must either increase the amount of exhaust gas flowing through the turbine or adjust the angle of the guide vanes more aggressively in order to achieve the desired boost pressure. However, it is important to consider air pressure and/or altitude.
It should only be measured under high load conditions, where the boost pressure control system actually needs to regulate something.

christians wrote:

I just don't know how much a catheter can get clogged and what kind of back pressure that creates.

Hi Christian,

There have apparently been several cases where the KAT monolith has fractured, and debris has become lodged across the outlet pipe of the KAT housing.

I can easily imagine that, in some cases, only fractions of the normal pipe diameter might remain open.

Hi Ulf,
That sounds pretty intense.
Regardless of how the turbo operates, a significantly excessive exhaust gas recirculation (EGR) rate would likely result, leading to increased soot production. Alternatively, it's possible that even less fresh air would be measured.

Hello,
I find the proposed LMM solution quite risky, as EDC initially seems to be trying to address the issue by increasing the intensity of the VTG staffing.
I also consider this to be a good indicator, but more as a before-and-after comparison, which isn't particularly helpful in this case.
Furthermore: increased fuel consumption.
Generally speaking, I would say don't worry too much about the cat; the pressure loss is negligible, and I can't imagine anything suddenly breaking off (other than maybe some debris) and causing a complete blockage.
We will have this kind of fun in a few years when everything is equipped with particulate filters .

Best regards, Albrecht.

christians wrote:

Regardless of how the turbo operates, one would still have an excessively high EGR rate, resulting in a corresponding amount of soot. Or alternatively, it would inevitably lead to measuring even less fresh air.

Hi Christian,

I don't believe the issue is with an excessively high EGR rate, because the engine control unit can reduce it (if necessary, the valve can be completely closed) until the mass airflow sensor reading returns to normal – assuming that's still possible.

Hi,
If he notices, that's good.
Otherwise, it would be a good idea to take it for a test drive, first under normal conditions, and then, for example, with a blocked exhaust pipe.
Christian.

Hello!

Has anyone here ever experienced a failing hard drive that wasn't detectable by listening for unusual noises?

Unfortunately, I experienced this issue with both my old gasoline Passat (with a 90 horsepower engine) and my new TDI Passat, and each time the rattling noise was very noticeable.

I never noticed any loss of power, by the way.

Regards,
Certainly! Please provide the German text you would like me to translate into English. I will only provide the translation.