Differential Pressure Sensor: Troubleshooting & Repair

Hello everyone,

"In my Polo 9N3 (1.4 TDI, PD engine), I've observed a phenomenon for about 30,000 kilometers that seems strange to me:"

The differential pressure sensor fails regularly after 8,000 to 10,000 kilometers. And by that, I mean it reports such high differential pressures on the DPF that it can no longer recover from the intensified thermal regeneration process. When I then install a new sensor, the regeneration cycle extends again to approximately 430 kilometers, but not more than that. I initialize the new sensor by turning the ignition on and off five times.

Do you have any idea what might be causing the sensor to malfunction repeatedly?
Here are some key details:

The DPF (Diesel Particulate Filter) was cleaned 40,000 kilometers ago.
I almost exclusively drive on the highway at speeds between 100 and 120 kilometers per hour.
Mileage: 454,000 km.

Thank you all!
Best regards,
Volker

What is the oil ash loading in the MSG (Molten Salt Reactor)?

Quote:

Mileage: 454,000 km.

Tap on the same cause as the previous poster.
DPF clogged, differential pressure too high...

stolley wrote:

Do you have any idea what might be causing the sensor to fail repeatedly?

I have an idea: thermal stress.
In many models, the differential pressure sensor is located behind a thermal protective cover. This cover is often forgotten to be slid back into place after a change or replacement. As a result, the sensor can sometimes overheat.

Alternatively, there might be a leak in the hoses near the sensor, causing hot exhaust gases to flow towards the sensor and heat it up. However, I would expect the hoses to melt rather than for the differential sensor to experience continuous failures.

Last resort: An unstable power supply. However, since I believe this is generated by the MSG (Main System Generator), I would expect to see other problems as well in that case.

As I said: These are just ideas, and I have no idea whether they actually relate to the issue or even could be related.

Regards,
Sure.

Here is the translation of the text from German to English:

"Guste" means "gust" in English. It refers to a sudden and strong gust of wind.

Hello everyone,

Thank you for your feedback regarding the DPF loading.
And what can I say? I think I'm partly to blame for the frequent need for recovery!

Ich habe nämlich nach Reinigung des DPF die Beladung offenbar ziemlich drastisch nach unten korrigiert: aktuell war der Wert auf 19g. Bei dieser geringen Beladung erwartet das MSG entsprechend geringe DIfferenzdrücke und reagiert bei höheren Differenzen mit häufigerer Regeneration. Sow"seit korrekt?" translates to "correct since when?" or "has it been correct?". A more natural translation would depend on the context. Here are a few options:

* "Has it been correct all along?"
* "Is it correct now?"
* "When did it become correct?"
* "Since when is it correct?"

I've temporarily adjusted the charge to 50g as a test.
What do you think about it?

Best regards,
Volker

Perhaps the DPF cleaning wasn't as successful as it should have been?
We can only guess, as no differential pressure values are known. Values measured at low load and under full load would provide some indication.
hg
Herbert.

That has nothing to do with opinion when it comes to real-world measurements.

We don't know how you cleaned, and therefore we have absolutely no idea how successful you were.

I've done this once before. In preparation, I often logged data extensively and generously, noting the approximate differential pressure during operation (of course, all estimates). But I also paid attention to how long a cycle takes until regeneration.


Before cleaning, I forced a regeneration cycle on the filter and then turned off the motor when it was finished. The rinsing process went relatively quickly, but it's hard to tell when you're done. If no more ash comes out, it might mean you've removed everything, or it could just mean that the remaining ash is stuck in the filter.


I tried that with a 7N, and it was difficult to get the welding wire around the curve to see if there was anything left in the channels. That was the case for every test.


After the installation was complete, I tried to calibrate the differential pressure sensor. I started driving with a load of approximately 20 tons and then corrected the reading after two regeneration cycles. After that, everything was working normally.


Therefore, it's difficult to guess.


However, you mentioned that the differential pressure sensor is constantly malfunctioning. Please check what previous commenters said about it. There might be an installation error, a faulty hose, or even a defect in the cable or control module. Measuring anything won't be useful if the equipment itself isn't working properly.

Hello everyone,

Thank you for your suggestions!
I will measure the differential pressure values soon and report my findings!

I also performed the cleaning process after forced regeneration. However, not a large amount of ash came out during the cleaning. The entire procedure was extremely time-consuming for this vehicle because it requires removing the complete crossmember and tilting the engine, etc. It took two full days.

I can rule out thermal stress on the sensor; it's completely exposed in the engine compartment of this vehicle. But thank you for pointing that out!

Okay, I've now determined the differential pressure values.

These are as follows:

Offset: -22.95

Idle: -20.40

Normal driving: -10.20

Acceleration: 20.40

Can you tell me something about these values?
By the way: What exactly is the offset value?

Hello,

The offset is the displacement from the printing zero point. Your differential pressure while driving is far too low. Negative values are physically impossible and usually indicate measurement errors (0 to -20 mbar). Larger negative values indicate a serious problem, such as an issue with the sensor circuit, wiring, or incompatible software in the engine control unit.

Please compare your differential pressure reading with the typical values listed in the pinned topic in this section and try to identify the cause.
Disconnected connection hose? Is the operating voltage at the differential pressure sensor okay?

Best regards, Rainer.

dieselschrauber wrote:

Please compare your differential pressure reading with the typical values listed in the pinned topic in this section and try to identify the cause. Disconnected connection hose? Is the operating voltage at the differential pressure sensor okay?

Hello Rainer,

Thank you for the tips!
I'm going to start looking into it and will report back!