DPF and Mass Air Flow Sensor: Explained

Hello everyone,
I'm just a hobbyist who's only worked on gasoline-powered engines so far.

I'm now experiencing issues with my Crafter 2.0 TDI while driving. First, the glow plug warning light came on (flashing), and a few minutes later, the engine control unit symbol illuminated (steady).

The engine then went into emergency mode, and I was unfortunately forced to drive another approximately 400 km with it .

The log is attached.
LMM = 3 errors.
and
DPF full.

Since I've owned it, the vehicle has been driven almost exclusively (90% of the time) on the highway for long distances. It has also been frequently used with heavy trailers.



My question now is about the correct procedure.

1. Are the two errors directly related? I have already replaced the LMM (likely mass flow meter) with a new one, but the error persists.

Can I regenerate the DPF (following the instructions here on the forum) even when it's in limp mode, and then clean or have it cleaned?

"Should I use a professional cleaning service offered online, or is it sufficient to simply clean with water after the regeneration process in my case?"

4. Can I still read the values for the DPF even when it's in limp mode? I believe it would show the ash content and differential pressure, if I'm reading this correctly from the forum.


Thank you for your help.
Regards,
Frank.

I also extracted some additional data blocks that might be relevant.

once in neutral.
once at approximately 2300 RPM.

The new LMM (likely referring to a mass airflow sensor) is not showing any readings, and the temperature is 25°C while the outside temperature is 5°C, with an intake air temperature of 155°C.

Does anyone have any ideas?

Hi,

The LMM apparently measures nothing.
Is it still drawing air through the mass airflow sensor, or is there a leak somewhere in the intake manifold?
Checked power supply to the mass flow meter/wiring?

A full DPF is a consequence of a malfunctioning mass airflow sensor (MAF) and prolonged driving with that issue.
Without an LMM signal, regeneration will not occur.

Once the LMM is working again, look for a message like "Load Limit Service Regeneration" or something similar.
If he hasn't already, it's still possible to initiate a regeneration process through the vehicle using VCDS.
Otherwise, the DPF unfortunately has to be removed.

Hello,

As long as there are faults related to air mass or intake air temperature, DPF regeneration is not possible, and the DPF will continue to fill up until it reaches its maximum capacity, at which point regeneration will no longer be possible.

LMM: Obtain the correct original part and check the wiring harness.

Best regards, Rainer.

Thank you both for your answers.

Then I now have a sequence of steps to follow.

Okay, I'll look into this and report back. I've already installed a new, original mass airflow sensor (MAF), but the problem is still there. I'm going to check the wiring and airflow now.

Regards,
Frank.

Sure, here is the translation of the text from German to English:

"Addendum:"
All wiring is okay, the air intake system is intact, and there are 5V present at pin 4 of the MAF sensor connector relative to ground when the ignition is on.

Am I making a mistake when clearing the error codes?
I have repeatedly cleared all the error codes, and also turned off the ignition afterwards.

LMM error persists.
Fuse checked, okay.

4- Fuse 34 on fuse holder C -SC34- 15A - Mass airflow sensor -G70- 7) Oxygen sensor 1 before catalytic converter -GX10- Control unit for NOx sensor -J583- Control unit for sensor electronics -J849- Control unit for NOx sensor 2 -J881-87

Okay, let's clear the error codes and see what errors appear when the ignition is turned on/engine is idling without the mass airflow sensor (MAF sensor) connected.

There are only 3 possibilities.
- LMM (lambda sensor) failure (unlikely if new and original, but very likely if the seller claims it "was working until it was removed," etc.).
- Damaged wiring harness.
- ECU failure (unlikely).

Best regards, Rainer.

Hello Rainer,
I followed your advice now.

THE LMM (Mass Air Flow sensor) is a genuine Bosch part - NEW.

Error memory cleared: Mass airflow sensor disconnected -> same error entry.

In the basic settings, there was a function... that was supposed to be executed after changing the LMM... I ran it, but the error persists.

The cables show no signs of damage.
The car is from 2017, and I'm ruling out a broken cable.
I've also never "tinkered" with the car in a way that would have caused me to create any wiring damage.

But, if I've read correctly, then 5V and 12V should be present at the outer pins of the connector. I can't measure the 12V .

Unfortunately, I don't have an ELSA wiring diagram. Would it be possible to simply connect the 12V directly from the battery to the mass airflow sensor (MAF)?

I've attached a few more photos. Could it also be related to the AGR valve? Shouldn't there be a fault code stored if that's the case?

Hello,

You can get wiring diagrams for your car from Erwin. You can also test the wiring harness all the way to the ECU.

Best regards, Rainer.

Okay, so...
The hose was checked again... and sure enough, it was actually pinched and disconnected at one point. It must have happened during the air filter replacement .

LMM is working again .

First of all, thank you for your support in resolving this issue.

I'm going to work on the DPF now.

I found the instructions for forced regeneration here in the forum, and I've attached the vehicle data below.


The calculated and measured values for soot mass differ significantly, so which one applies in the case of overloading?

Can I still perform a forced regeneration, or do I need a new DPF, or should I send the current one for cleaning?

Are there any experiences with professional cleaning services?

Hello,
"Recently, I had a Passat that wasn't regenerating properly due to a faulty exhaust gas temperature sensor, and it had accumulated 68g of soot (the limit is 45g)."
Forced regeneration was not possible because the particulate matter load was too high. I then connected a different differential pressure sensor and mounted it in the engine compartment. After about 15 km of driving, the engine control unit (ECU) indicated a particulate matter load of around 30g. I then plugged the connector into the correct differential pressure sensor, and forced regeneration could be started. I was able to take a long drive and the filter was cleared.
I don't know if this would work for you. Since VW mandates the replacement in such cases due to a fire hazard, my description should not be understood as a guide. Any attempt to replicate this is done entirely at your own risk.

Best regards,
Sören

Sören,
"Thank you very much."

I'll think about it.

On the other hand, the vehicle already has 170,000 km on the odometer, it's the first DPF (Diesel Particulate Filter), and the ash load has already reached almost 80 out of 110. Regarding back pressure, fuel consumption, and performance, one definitely needs to consider these factors.


Therefore, we are now considering replacing the DPF.

Regards,
Frank.

Hi Frank!

To be honest, for a long time I considered all these offers regarding cleaning, whether through washing solutions or "ozone" treatments, to be a scam and nonsense.

I actually tried it out recently and had the filter from my CFFB cleaned.

The readings from the differential pressure sensor have shown a significant improvement, so it's questionable whether you absolutely need to buy a new DPF. The cost difference between cleaning and a new part is also a factor, and it's roughly a 1:10 ratio if you want to buy an original DPF (which is recommended...).

It was important to me that the provider could somehow demonstrate the quality of their work or the performance of the machine, so when choosing a provider, I made sure that they offered a before-and-after testing protocol with back pressure and flow rate measurements for comparison.

Anyway, the DPF should ideally be freshly regenerated before undergoing "external" cleaning, so you probably can't avoid that.

Have a good evening.

Alex.

Alex,
"Thank you very much!"

I have also decided to have the cleaning done. The new parts are extremely expensive .



I'm going to work today and try to recover and improve.

I will then report...

Regards,
Frank.

So, somehow the regeneration process isn't working, neither when the vehicle is stationary nor when it's in motion.

No error is displayed, or the process is terminated due to a missing requirement.

When I start the particle filter regeneration service in the basic settings, VCDS displays "Running".

but the values for exhaust gas temperature... (see pictures)

The value for soot mass does not change; in fact, it increases.

Is that due to the photo, or does the second image show a value of -40 degrees for the "particle filter outlet temperature" parameter?

ZTurbo wrote:

Is that due to the photo, or does the second image show a value of -40 degrees for the "Particulate Filter Outlet Temperature" parameter?

Check if this is a calculated value or if it actually comes from a sensor (check it!).

Otherwise: Should regeneration be enabled during driving instead of when the vehicle is stationary?

Please provide the text you would like me to translate from German to English.
Okay, I'm ready. Please provide the German text you want me to translate.