AD Blue Fehler immer wieder | Posts 32+

dieselschrauber wrote:

Quote: Current temperature in the NOx reduction catalyst: --- 25 25 25 25 25 25 25 1.5 1.5 1.5 1.5 1.5 1.5 Here's the first strange thing: why 25°C specifically? It looks like a replacement part to me, so I would check to see if other vehicles with the same engine exhibit the same behavior. Ideally, the problem would be a broken cable or a loose connection to this sensor, or a sensor defect. However, in such cases, a corresponding error message should ideally appear. Perhaps someone from the forum has already looked at this or can comment on the behavior. For me, it's not plausible why a temperature that is initially too high is displayed. Best regards, Rainer

I think this is a default setting because the sensor is designed for temperatures above 1000°C, and the characteristic curve is too inaccurate/deviates too much at lower temperatures, and it's also not necessary in that range. Therefore, also the...
Rectangular ascent. If it were a measured value, it would increase linearly because of the PTC (Positive Temperature Coefficient) effect.
A cable break can be ruled out, as there have been no interruptions in operation since then. And if that were to happen, which is certainly monitored, there would be an error entry.

So, it ultimately boils down to the SCR system. The new nozzle is installed, but it's exhibiting the same behavior, so we can rule that out as the cause.

It's also interesting to pay attention to the fuel level indicator. It's usually constant at 80%, but occasionally jumps to 50%. My guess is that when driving in curves, the top indicator rod sometimes comes out of the fuel, showing 50% because only the lower rods are wet. This means I've already driven 30-40% of the distance. However, even if that were the case, the system would still need to function, and it doesn't explain the shutdown that occurred a year ago.

Best regards, Thorsten.

I wish everyone a healthy and successful 2024.

There are a few new experiences.

So far, I've been able to continue driving. I've only been driving to and from work, and only up to a maximum speed of 100 km/h, and the SCR temperature has been limited to a maximum of 230°C. I smelled something like ammonia coming from the AdBlue tank. So, I refueled as much as possible and topped it up with fresh AdBlue. However, this didn't change the readings. It seems like almost all of the raw emissions are getting through. At 100 km/h, the NOx concentration is approximately 300-400 ppm, with a SCR temperature of around 200-230°C.
According to some bachelor's and master's theses, approximately 80% conversion should occur at temperatures above 200°C. I've searched the web and found a source in Austria that still has an original, unused SCR system. It's already in my basement. Today, I drove on the highway and intentionally "exceeded" the limits. I drove at 120-130 km/h with the SCR system at 250°C, and surprisingly, the countdown started immediately. On the way there, everything was green in the dashboard display. Shouldn't it first count up internally? I looked at the efficiency ratings in more detail a few weeks ago. The currently installed SCR system (used, original VW) showed efficiency ratings of 0.1 during the measurement phase, which is below the target of >=0.3. Okay, I'll install the new one on Friday (it has the date 2020 engraved on it). I'm excited. Now it's new and original, and it won't be possible to get something like that again. But on the other hand, that was also the point where the most expensive parts came into play.

Here's the translation:

Another question: For the regeneration of the stored NOx in the SCR system (which is a storage catalytic converter system, right?), the engine's air-fuel mixture needs to be adjusted between rich and lean. Could an aged oxygen sensor potentially be the cause of the registration issue?

Best regards, Thorsten.

Okay, the new, original catalytic converter is installed. At 223,459 km, approximately 30 km after installation and a highway drive, it cleared the error code, just like before. The live data showed efficiency values of 0.7 to 0.9 at a catalytic converter temperature of around 300°C. Let's see if that remains the case.
Best regards, Thorsten.