CAYC, high consumption, registration too frequent, no error in MSG

Hello everyone,

I'm having a "small" problem with my Passat.

The vehicle: Passat.
B6, year 2010, 1.6 TDI BlueMotion Highline, all original, accident-free, mileage: 369,000 km, 5-speed.
Purchased in March 2017 with 204,000 km.
Engine: CAYC, no modifications, everything original. Oil and oil filter changes every 15,000 km, using Aral SuperTronic K 5W-30.

Until these problems started, everything was fine. At 165,000 km, there were no error messages from the engine.
Zero oil consumption (0.5 liters / 15,000 km), no oil increase.
No water consumption for cooling.

The problems:
1. Wave-like driving with/without cruise control at a constant speed.
Consumption display fluctuates, ± 1.8L at 80 km/h, and also at other speeds.
2. Excessive fuel consumption, calculated as .5 liters per kilometer.
Consumption measurement since purchase.
3. Fuel consumption displayed during normal operation, showing 49.9 liters per kilometer in first gear.
When shifting into 2nd gear, approximately 38 liters per kilometer, etc.
4. DPF regeneration every 200-300 km (at 24g = 100%).

These problems still occur despite the use of new components.
No error messages stored in the MSG (Message System), and no warning lights illuminated.

What has been done so far:
1. DPF is brand new, original VW, manufactured in October 2024, and installed at 362,150 km.
Here, for the first time, an error message appeared with a light indicator.
Okay, considering the time elapsed and the mileage.
DPF values reset, VW workshop.
2. New, original VW differential pressure sensor, model G505, manufactured in February 2025, with 365,300 km mileage.
DPF pre-filter / differential pressure sensor checked, OK.
Display: Engine off: 0 mbar.
Engine idle, DPF 20%: 0-1 mbar.
Engine idle, DPF 83%: 3 mbar.
Engine at full load, DPF 91%: 171 mbar.
3. Oxygen sensor G39, new, NGK, 02/2025, mileage 365756 km.
4. Coolant temperature sensor G83, new, original VW, 02.2025, 365756 km.
5. Mass Air Flow Sensor G70, new, Pierburg, 02/2025, 365804 km.
6. Pressure sensor N75, new, original VW, 03/2025, 366145 km.
7. Throttle body G69, new, Valeo, 03.2025, 367722 km.
8. AGR intake manifold/pipe, new, original VW, 03.2025, 367722 km.
The deposits in the EGR valve housing were also limited.
I would have expected more given the mileage.
9. Coolant temperature sensor G62, new, original VW, 03/2025, 367722 km.
10. MAP sensor G31 / G42, new, original VW, 03.2025, 367722 km.
11. Coolant thermostat, new, original VW, 03/2025, 367722 km.
12. Battery EXID, new, 05/2024; (suitable for start/stop systems).
13. Air filter / fuel filter replaced, MAHLE, 10.2024, at 362,150 km.




Reviewed / Monitored:
- The engine starts immediately when cold, then idles stably with a slightly higher idle speed.
Power consumption varies depending on the connected device, ranging from 0.4 to 0.7 liters per hour.
- The hot engine starts immediately, then idles smoothly with a normal idle speed.
Consumption rate depending on the connected device: 0.2 to 0.3 L/h.
no consumer = 0.1 to 0.2 L/h at idle.
- Full start/stop functionality, automatic engine shut-off, normal start with clutch engagement.
No start/stop functionality if the prerequisites are not met.
- Fuel consumption display: 0.0 L/h in motor-driven mode.
- EGR valve: 100% / closed when: engine off; full load; regeneration.
- Exhaust temperature sensor before and after the DPF in a cold state = ambient temperature.
Regeneration at 650°C / 590°C.
- DPF before regeneration; starts at 24g and 100%.
- DPF after regeneration; ends at 3.88 – 4.6g and 16 – 19%.
- Only when regeneration is occurring will it also be displayed after injection.
- The car accelerates normally, with sufficient power, up to its maximum. Boost pressure is being achieved.
- Coolant temperature 90°C and oil temperature 95°C after 5-7 km; with an ambient temperature of 16°C.
- Vacuum lines checked; OK.
- Crankcase ventilation system blocked, test drive performed -> no improvement.
- Air intake checked, OK -> using a smoke machine.
- No evidence of weasel damage or presence.
- No biodiesel was added.
- No external mechanics or workshops have worked on the Passat.
- only one driver.
- Original suspension; original tires/rims.
- original sound system, no electronic modifications.
- Cleaned up mass points in the engine compartment.
- Checked plug/cable.
- Alternator regeneration OK -> Charging voltage curve checked.
- The engine is dry, with no oil, fuel, or coolant leaks.
- The engine software update for the EA189 engine was already installed on January 2017, at a mileage of 202,602 km.
This software is still installed, and there are no apparent issues.
- The deposits in the old throttle valve were not very thick, only 2-3mm.
- The 2nd. The coolant pump for the AGR system runs for a short time after the engine is turned off, which is normal.
- The radiator fan runs when the engine is turned off, and it stops as expected during a regeneration interruption.
- Driving profile: 26 km one-way distance for work, mostly country roads/highway; no stop-and-go traffic.
I live in the countryside, so the distances are always longer, and there's no taxi service for children.
Average speed since purchasing the car: 59 km/h.
- Tools: Bosch OBD150; VAG-DPF; no VCDS.
So far, that has been sufficient.

I have tried my best to provide a comprehensive explanation.
because good preparation leads to good results.
In this spirit, best regards.

Hello,

Welcome!

Please log the following data during the fluctuating behavior: engine speed, fuel injection quantity, actual air mass, target air mass, and actual/target boost pressure. Can the target rail pressure be adjusted, and is it stable when the injection quantity remains constant?

Perhaps it would also be worthwhile to check if the measured value is consistent with the accelerator pedal position. So, 0% corresponds to no gas pedal input, 100% corresponds to full gas pedal input, and at the same gas pedal position, you should have a consistent, non-fluctuating gas pedal percentage value.

What is the oil consumption per 1000 km? Does the engine reach its full power/maximum speed?

Best regards, Rainer.

Good evening, Rainer,
Thank you for your contribution.

Regarding your questions:
- What is the oil consumption per 1000 km?
I wrote about that above.
Approximately 0.5 liters per 15,000 kilometers.
Nothing was added between oil changes.
- Does the engine reach its full power/maximum speed?
+ Performance, I would say -> yes.
"It's fine up to 180 km/h, but after that, the Autobahn ends."
or traffic conditions do not allow it.
+ Previously, with the engine running, the speedometer (digital display) showed 200 km/h.
If it's included, I will check it if possible.
-> should be achieved.
The Passat is equipped with a 1.6 TDI engine producing 105 horsepower.
- To perform a log analysis, I need to acquire a different diagnostic tool.
Mine can only display one channel at a time.
Show, but don't save.

But this will then be implemented.

We already have an idea about the very high fuel consumption during startup.
I searched online (worldwide) for information on this specific topic, and the result was 49.6 liters per hour.
12 entries found, but unfortunately, no results were found.
Only the exact effects were described, and many components were also replaced.
and it all amounted to nothing.
Then, each time, the blog would come to an end.

You're welcome.
Greetings.

Quote:

For log data, I need to acquire a different diagnostic device. Mine can only display one channel at a time. Show only, do not save.

Well, you know the engine speed and the throttle position, but we can't see that.

What would be interesting to me is how the boost pressure and rail pressure regulate, but you don't seem to know what's considered normal.
Here in the forum, you should be able to find some logs (images) related to this. Regardless, the regulation process should generally be completed in less than 1 second, and over the long term (after more than 3 seconds), the regulation difference should be less than 2%. For example, the target pressure is 2100 mbar, while the actual range is 2058 - 2142 mbar.

P.S., A common issue with older cars is a leaky charge air cooler (CAC) or intercooler hose. When running at full load, if it makes hissing noises, then exactly this happens: high power consumption, and the regulator cycles too frequently.
A leaking LLK (charge air cooler) / intercooler hose can be identified by oily spots (as the KGE ventilation system connects to the intake manifold).

Good evening.
Thank you for your submission.
To your notes:
- Air leaks in the charge air system.
Everything is dry along the intercooler and there are no unusual noises.
-> I had a similar issue on a Passat 35i with a 1Z engine; the intercooler hose burst.
- The KGE (likely referring to a catalytic converter or similar component) was disconnected for a test run and the intake side was blocked, but there was no change.
Still experiencing fluctuating consumption even at a constant speed.
49.9 l/km during normal starting .

As mentioned before (to Rainer), a different diagnostic device will be used for the log voyage.

Are there any other ideas about which values should be included?

"This issue has also occurred in other owners of VW TDI vehicles."
But, as previously mentioned, there are no solutions for this error.

In this spirit.

Best regards,

Quote:

or hints; this issue has also occurred in other owners of VW TDI vehicles. But, as already described, there are no solutions for the error

.
Just because the word "solution" isn't in the title doesn't mean the problem hasn't been solved.

First, examine the mentioned items and see where the "waves" are coming from.

Hi,
The 49 l/100 km fuel consumption during startup isn't that dramatic. It's 40 l/100 km.
I can also achieve that with the DDYA (1.6 CR TDI EA 288)).
What's noticeable is the 0.1 to 0.2 liters per hour consumption at idle. That would mean 1 mg per injection, and I simply don't believe that.
The amount of fuel injected is calculated based on the rail pressure and the injection duration. Either the rail pressure is significantly higher than what is being measured, or the injectors are leaking.
In addition to the already mentioned data such as target/actual rail pressure, injection quantities, and idle correction values, the system should also determine shift time correction values, hold pressure (for injectors that are open), and return flow rates.
hg
Herbert.

Hello everyone,
Still the same problem.
Here are some pictures of the power consumption display.
1. Idle; Car stationary = 0 km/h; Engine warm.
2. Normal acceleration, accelerator pedal depressed 1cm, speed 10 km/h.
3. Gas pedal held down, not pressed further.
accelerated to 15 km/h
-> Jumps directly to 49.9 L/100km.

Greetings.

Here are the pictures.

That's nothing new in your thread. Why don't you answer our questions? Your parts-swapping frenzy without a proper diagnosis achieved nothing.
hg

Good day to everyone,
First of all, many thanks to the many readers, over 5700.
Unfortunately, only two readers (Rainer and Herbert) submitted comments.
But let's go through it step by step.
Since I didn't have the right tools available, I decided to take it to a specialized workshop.
to entrust with that task.
Ultimately, the 1.6 TDI CR engine, specifically the CAYC variant, is not some exotic piece of technology; it has been mass-produced millions of times.
I found a workshop that's available, but it's 60 km away.
I had previously sent the description of the problem to the workshop foreman, and he said:
Everything's fine; he already had a few ideas, and he was capable of achieving much more.
Okay, I'll just leave it as it is.
So, we went there, and then it started... I was there the whole time.
Statements:
- The engine runs well, very smoothly, and starts immediately.
- Your description is accurate.
- and after 2.5 hours of searching, using diagnostic tools -> VCDS and LAUNCH,
He was really diligent about it, always trying, measuring, and comparing values, etc.
 I can't find any errors; the engine is fine. There's also no error in the control module (MSG).
- My question: And what happens now?
Continue driving until an error message appears in the MSG (Multi-System Gateway), or until you reach another workshop, or a VW dealership.
Thank you for...
Now I know why, but I'll tell you more about that later.

After that, I went to three independent workshops and four VW workshops.
Overall, this didn't lead to success, and some parts were still exchanged.
All VW original parts.
The ideas were good in principle, but it was always said that it might not be possible.
Statements were made such as:
- You don't always have to start with full throttle; it will work out fine anyway.
After the test drive, yes, mmmhh...
I need to check that out; it seems to be exactly as you described it.
- If the error description is like this, we will reject the repair request.
"No error codes in the MSG (Multi-System Gateway), and so many parts have been replaced. That's what VW said."
- Sell your old car to us, or buy something new – we have a wide selection.

Oh yeah, the warning light came on, but I was feeling optimistic.
It was the first exhaust temperature sensor (sensor 01) that needed replacement, and the replacement didn't require any adjustments.

In the meantime, the following has also been:
14. MSG expanded, connector in good condition. MSG was still secured with breakaway screws.
MSG dry, no water damage, MSG cover plate was installed.
15. Mass points in the water reservoir under the windshield, cleaned; pole grease.
16. Water tank cleaned, drain openings cleaned.
17. Accelerator pedal G79 G185, new, original VW, 06/2025, 371548 km.
18. Fuel pressure sensor G247, new, original VW, 06/2025, 372177 km.
19. Exhaust gas temperature sensor, new, original VW, 07/2025, 372450 km.
20. Clutch, complete; Dual Mass Flywheel (DMF); New gearbox oil, Sachs, 07/2025, 373,200 km.
21. Crankshaft sensor G28, new, original VW, 07/2025, 372450 km.
22. Crankcase ventilation membrane, new.

- The clutch needed to be replaced, and while it was being done, the crankshaft sensor was also replaced.
because it works very well that way. Of course, the power connector and polarity switch were also cleaned. Because the entire process took 4 hours, the MSG also lost power and underwent an internal reset.

- Regarding the accelerator pedal, it was mentioned that the engine responds abruptly/spontaneously/aggressively.
The sensors might be sending incorrect values to the MSG -> needs to be redone.

- In addition to the standard oil, LIQUI MOLY 5120 was added, covering a distance of 5000 km, and the engine running smoothness had improved.

- TPI: Tested for 1.6 TDI CR and 2.0 TDI CR engines. Any other suggestions?
Okay, and another AGR simulator was installed by Tafment in order to verify the statements and assumptions.
It's probably the EGR valve that's faulty, which is why the engine is behaving like this. This can help clarify things.
It's easy to install; it simply snaps into place with locking plates, and everything is reversible.
What can I say, it's been installed for 3000 km and nothing has changed.
The AGR is not the cause.

Unfortunately, nothing has improved; there is still increased consumption, and the battery regenerates every 250 km.
Only the wave-like motion with or without cruise control at a constant speed is no longer noticeable.

- Well, at least this whole thing has yielded some measurements.
Injection volume deviation is within acceptable limits. See appendix: +/- 0.6 mg/stroke.
Return flow is within acceptable limits.

In other words, all the effort ultimately achieved nothing, so we have to do it ourselves.

In the meantime, I was able to borrow a LAUNCH CRP 129 EVO diagnostic tool for a few days.
Unfortunately, no abnormalities could be detected, and the handling is not great.

So, I've been looking into VCDS and trying to figure out what each feature is used for.
At the VCDS (Vehicle Diagnostics System), the relevant data parameters were correct, so I obtained the necessary documentation and information on how everything works.
Ordered a VCDS / laptop and am full of anticipation for what's to come.
after a four-digit amount has been transferred.
Installed/connected/downloaded everything and registered VCDS; it worked well.

Okay, here's the translation:

"Now here's the thing: the MSG in the CAYC is from Conti and doesn't have a MWB!"
The fuel injection system in the CAYC is also supplied by Conti.

Therefore, no comparison values or limit values can be displayed, as these are only available in the MWB (presumably a specific document or system).
Here, only the "extended measurement data" field is available; the measurement block 08 field is grayed out.
Why? -> Because MSG has the UDS protocol.
When displaying measurements, only values with units or binary code are shown.
and without value ranges and without target values, it's just useless.
There are some expected vs. actual values for comparison regarding the IDE numbers.
- Boost pressure
- Fuel pressure.
- Air mass
- Exhaust gas recirculation.
- Throttle valve
- Exhaust flap
- Steller Turbocharger
- Engine speed
"638 lines are displayed with IDE/ENG numbers, but only approximately 150 are being transferred."
populated with values. Some values are still being displayed redundantly (with different IDEs).

That explains why the workshop couldn't make any progress during the inspection.
If the technician can only read actual values and only has access to a small number of setpoint/actual value comparisons...

My question is, where can I find the threshold values / target values?

Therefore, I can answer questions and provide guidance on:
# Rainer, all the target/actual values that are displayed in VCDS show no anomalies.
# Herbert, Rail Pressure Setpoint/Actual Value -> No anomalies detected, see also the attachments.

So, I've presented all the news about what has happened in the last 4 months.
Ideas/suggestions are welcome, don't be shy, just write.
In this spirit,
Best regards.

Here's the attachment.

ZEHST wrote:

Therefore, I can answer questions / provide information about: # Rainer, all the target/actual values that are displayed in VCDS show no anomalies. # Herbert, Rail Pressure Setpoint / Actual -> no anomalies detected, see also the attachments

Please read through the following articles on guided troubleshooting.

Your essay reads as extremely verbose, and you seem surprised by trivial matters. On the other hand, you don't present any facts or evidence to support your arguments. "No abnormalities."
Every workshop should be familiar with using the extended measurement data, including target and actual values.

The questions from Rainer and Herbert weren't about a simple comparison at a single operating point. Instead, they wanted a complete test run with a time-stamped recording of the target/actual values (see the technical article). Based on the recorded data, not only the static behavior that you probably want to compare can be checked. The focus is explicitly on the fluctuations that occur during the run. To do this, it's also necessary to analyze the values dynamically over their time course (with the highest possible resolution, meaning only combining a few meaningful measurements).

If you're genuinely looking for help in a specialist forum, simply acquiring the necessary equipment will get you quite far (done). However, you also need to be able to use it correctly. These articles can be helpful in that regard.

Overall, I am confident that we can help you in the forum. However, to do so, we need numbers, data, and facts in the form of logs from you. Sure, here's the translation:

"No prose."

Hi,
The engine control units (ECUs) of common rail engines do not have measurement value blocks. That's why you won't find any.
You need to create measurement groups for various purposes by selecting them from the extended measurement values, and you should then save these groups. A maximum of 13 values are possible, but that's usually too many. The next prompt is then "Load from file."

VCDS runs on any laptop, even older ones you might have in the garage. The battery just needs to have enough runtime, or you can simply use a 12V to charging voltage converter.

First, you should post an initial scan here so we know what we're talking about.

And then a recording (snapshot) with information on engine speed, engine temperature, average fuel injection volume, and fuel injection volume deviations.
Your values look good, but the average emission level is missing, and I had already been wondering about your low fuel consumption before.

Here's a snapshot with particle filter data: Differential pressure, Particle filter: Offset for differential pressure, Particle filter: Oil ash volume, Particle filter: Calculated soot mass, Particle filter: Measured soot mass, Particle filter: Kilometers since last regeneration, Particle filter: Fuel consumption since last regeneration, Load limit for field regeneration, Vehicle mileage: 139458 km, Particle filter: Oil ash mass.
The values should appear in ascending order.

And just like that, you've created two different groups of measurement values.

hg
Herbert.

Hello guste100,
Thank you very much for your reply.
I'm quite surprised to read something like that from an experienced mechanic and long-time forum user.
So much text with so little content.
In the past, in another post, you...
contributed with expert questions and suggestions to help find solutions.
Sorry for wasting your time, but if you happen to think of anything else related to the topic, please feel free to write.
Note: There is no information available throughout the entire forum regarding target values -> extended measurement values.
Believe me, I've been searching.
I'm not sure if the absence of something related to the topic of "MWB" is a trivial matter.
Okay, that's a matter of opinion.
Please see the attached "VCDS Function Overview" document, where you can clearly find the information.
VCDS; 08-Measurement Block; UDS; Yes.
This error should be corrected.
Surely, as a buyer, one would start to get suspicious at that point?
Herbert described it in great detail in his subsequent post.
I will address his questions later.

Guided troubleshooting only makes sense if I also have a defined range of values and a target value.
The actual measured value is being transmitted.

The values where a target/actual value is transmitted along with an IDE number have already been compared.
Note: The MSG data from CAYC only transmits current values, and nothing more.
and only a few target/actual values.
I wrote that there were no anomalies in the setpoint/actual values.
This means slight deviations, which are less than 2-5%.
- When idling and at other speeds while stationary.
- Constant speed.
- During acceleration.
Sampling with Turbo mode and only 2 values each (equivalent to four IDEs), otherwise the whole process is too slow.
"Workshops have done similar things, but... nothing came of it."
If the repair were that simple, it would already be finished.
Info: If my topic/thread is boring or irrelevant,
"Otherwise, so many users wouldn't read it."
The topic of "extended diagnostic data" in relation to UDS is currently very relevant in this forum.
See the post about extended measurement channels for VCDS via UDS, which has been viewed over 12,000 times.
Unfortunately, this post only provides instructions on how to link to 12 channels.
"to transmit once in a query. -> But no setpoints."

@ Herbert: Your post is simply very good; this is how new owners of VCDS should be introduced.
Here's the translation:

"Also, the link with the Autoscan feature."
Following the motto: Treat your people the way you want to be treated.
I will answer your questions one by one, now that I have VCDS.

There are many readers again, but so far, only three have written something.
Okay, it only needs one solution .
Autumn greetings.

Hello,
Sure, here's the translation:

"P.S." or "Addendum."
The following things were also done:
23. Oxygen sensor G39, new, NGK, 09/2025, mileage 376004 km.
24. Mass Air Flow Sensor G70, new, original VW, 09/2025, 376601 km.
Why?
During the installation of the AGR simulator, a very heavy layer of soot was discovered inside the tubing.
This carbon buildup can also be found on the oxygen sensor.
When the AGR piping/throttle valve was originally installed, the carbon buildup was not as severe.
In the tech industry. The description of the broadband lambda sensor indicates a potential measurement error due to heavy soot or ash buildup on the sensor body.
Therefore, I'm trying it again -> it didn't work the first time.

The first mass airflow sensor was made by Pierburg, and is now an original VW part.
The value display/transmission is much sharper with the VW mass airflow sensor; faster, ...
There is definitely a difference in the transmission.
It's either original VW, a replica, or something else... I can't recommend it anymore.
The quality of these components has only deteriorated over the years, and...
Modern engines rely on precise measurements.
The LMM primarily plays a role in the combustion process.
If inaccurate or inappropriate measurements are already being transmitted to the MSG, then nothing will work.
Following the motto: "Garbage in, garbage out."
Therefore, I'm trying it again -> it didn't work the first time.

More information will follow.

Sunny autumnal greetings