Turbodiesel Failure: VW Passat 2.0 - Symptoms & Causes

Hello diesel mechanics,

I have an exciting story for you and I really need your help.
"For a few months now, we've been borrowing our in-laws' well-maintained VW Passat Variant 2.0 from the year 2006, and we certainly don't want to return it as a total loss."

The increasingly erratic driving behavior and the smell had long indicated that something was not right. However, several workshops, including two VW specialist workshops, had already repeatedly and unsuccessfully searched for faults or causes. In the process, parts were repaired and replaced that were not actually defective, and the actual fault has remained.

Symptoms:
- The engine usually takes longer than normal to start, and it sounds irregular during the starting process.
- Erratic idling and low-gear behavior (engine speed fluctuates).
- Spontaneous, wave-like or jerky acceleration (in 3rd gear at 50 km/h).
- Sometimes the car drives so roughly that you can feel the jolts in the steering wheel and get shaken up.
- An enormous, persistent stench (biting, toxic, smokeless - like a suffocated barbecue).

Error memory:

No errors found that correspond to the symptoms. The only error code that should be mentioned for the sake of completeness is: P0299 - 006 - Boost pressure control, limit below threshold.

"This error could be reproduced: when accelerating in 6th gear at 2200 rpm, the turbocharger could no longer reach the desired boost pressure, and the engine went into limp mode. Consequently, the air ducts/lines were replaced, and the seals were renewed."
The problem with the turbocharger pressure regulation seems to be resolved, but the symptoms (smell, erratic running) persist.

Serious new evidence:
Yesterday, while changing the air filter and diesel filter, there was a nasty surprise: The diesel filter was completely clogged with black oil. We had seen something similar before community.dieselschrauber.de/viewtopic.php?t=267488O, where a crack in the tandem pump was suspected.
(A check of the current oil level was okay.)

During the first short test drive after replacing the filters, without having driven any kilometers, the turbocharger's power completely disappeared without any error messages, accompanied by strong, white clouds of smoke from the exhaust that smelled like plastic. --> Is the turbocharger dead? [url] [/url]

Attached is a VCDS log/recording from that trip without the turbocharger.

Tomorrow, we will have to open everything up and disassemble it (turbocharger, tandem pump, etc.), without having a clear idea of what caused all the previous symptoms and the final failure.
Debugging can be very expensive, and the repair, if you rely on the wrong information, is even more so. Due to the lengthy history, many people have already been racking their brains, so now it's time for the real professionals to step in .

Thank you very much in advance.
Mags.

Hi!

What is the mileage of the Passat?
Engine identification codes?
Last service?

It seems like the vehicle has been somewhat neglected.
"When I look at the fuel filter!"

I wouldn't just ignore that error message!
Try accessing the VTG (Valve Train Geometry) in the actuator diagnostics!
Perhaps this will help!

Und mal die unterdruckschläuche kontr. Maderbiss??

Best regards,

Good evening.

vagturbo wrote:

It seems like the vehicle has been somewhat neglected. when I look at the fuel filter!

Not particularly helpful statements! He had written that engine oil was in the diesel filter. You can "wait" as little or as much as you want, but that normally doesn't get in there.

The engine is a 170 hp TDI with Piezo common rail injection (Siemens VDO, now Conti). The engine code is BMR.

My suggestion would be, in addition to checking the tandem pump, to examine the idle speed control values (MWB13) and the injector switching times (MWB23).

The amount of air being drawn in is far too low. Are the throttle valve and EGR valve functioning correctly?

Best regards, Rainer.

Okay!

You're absolutely right!
But it can only form one air mass if...
The turbo is working properly and is therefore drawing in air.

And in the log, it doesn't seem to be the case, or am I seeing something wrong?

vagturbo wrote:

Okay! You're absolutely right! But it can only form one air mass if... The turbo is working properly and is therefore drawing in air. And in the log, it doesn't look like that, or am I seeing something wrong?

In his log, at idle speed, the actual air mass is found to be 120-180mg/H, and the turbocharger plays no role in that.

Therefore, I would first like to rule out any problems with the throttle valve/AGR system or other "blockages" and check the relevant components.
Is the wiring harness at the mass airflow sensor okay?

Best regards, Rainer.

Thank you for the quick, helpful answers and the analysis of the logs. In fact, there is already a first success, because the tip about the LMM led us to the right track.
A small, thin film had gotten stuck in the intake manifold's screen, behind the filter, and it must have come from the new "quality" air filter. I should have checked better to see if anything was attached to the filter...
At least this one problem is solved - the engine is getting air again, and the power is back - but the old symptoms, as listed above, remain.

Tonight, as discussed, we will examine the tandem pump, the idle speed control values, and the injector switching times in order to identify the root cause of all the symptoms.

Best regards,
Mags.

Hello Mags,

It's possible that the problem lies with the turbocharger boost control, the unusual power delivery, or the regeneration issues (smell) are consequences of the temporarily low air mass values.
I'm rooting for you!

There's still the issue of the black sludge in the diesel filter, and the tandem pump needs to be checked.

Edit: The above applies if the filter shown is actually the diesel filter. However, in the first picture above, it can be seen that the diesel filter is screwed on. The oil filter and the diesel filter look very similar in this model, as shown in the picture. I have been informed that the filter shown is supposed to be the oil filter, but this is difficult to discern from the picture.
I assume, hopefully, that no one is tinkering with an engine while confusing the oil filter with the diesel filter...

Best regards, Rainer.

Hi.

The motor has software version 1881.
She is very old, and she definitely did not participate in PPDE action 23H9.

Furthermore, I believe that the screw on the intake manifold is greasy and oily on the left side, and that there is some oil residue on the alternator.
This indicates a broken swirl flap adjustment shaft, which explains the boost pressure error.

... I still need to check the logs.

Is the "constant pressing of the accelerator pedal while the car is stationary" a waste of time, or is it "dangerous"?

Lambda is ALWAYS at 1.02 -> I don't believe that, or it's broken .

EDIT:
1.02 is the fixed value during the initial cold start, before any measurements are taken.
-> The log is uninformative.

m;

Hello, dear Diesel Mechanic Team,

Thank you very much for your helpful answers back then.
The Passat 3C still exists, but don't ask about the price ; in this case, it was more about the principle .

We then tried to get to the bottom of the cause of the errors (primarily the wavy/jerky acceleration) by any means necessary - which ultimately led to us completely replacing the engine . Here is a brief summary of how it happened and what we did:

- First, we updated the software on the control unit.
- and replaced the wiring harness of the PD (Pressure Diode) elements.
- After that, we had the PD elements professionally cleaned at VW.

When everything still didn't improve, and the wave-like acceleration up to 2500 RPM persisted, we...

- Have the PD elements at VW specifically checked -> two of them were very clogged despite cleaning.
- At the same time, we inspected the cylinder head gaskets and found a crack in a cylinder wall.

At this point, it would have been the right time to dismantle the car for spare parts, but we had obtained a new engine (80,000 km) at a very good price, and we thought we could overcome everything with it.

- Installation of a new engine (including turbocharger).
- Cleaning of the DPF

The new engine ran very smoothly after installation, as expected, but as you might guess: the good luck didn't last long.

More on that in the next section.
Best regards,
Mags.

Hello, dear Diesel Mechanic Team,

Here is the continuation, as announced, with the current status of the problem.

So far, quite noticeable...
Since the new engine was installed, the only issue has been that the DPF (Diesel Particulate Filter) needs to be cleaned regularly (approximately every 500 km).
The automatic cleaning cycles were repeatedly interrupted, accompanied by the well-known, enormous stench (acrid, toxic - like a suffocated barbecue).

Just about a year after the Passat started driving quite well, now comes the big disappointment:
The independent, wave-like/jerky acceleration is back!

Error message:
"Fortunately," this time accompanied by an error message in the error memory:
Boost pressure sensor: P1592 - 006 - implausible relationship. And based on that: vacuum leak in the intake system.

Pressure sensors in the intake manifold and a pressure sensor in the control unit provide very different pressure readings even before the engine starts -> therefore, it is clearly an implausible relationship. However, the mass airflow sensor (MAF) provides plausible values.

So far, what has been done:
- (The car battery is new.)
- Checked for leaks in the hose.
- Mass points, mass cable, battery terminal > Body checked and renewed.

Planned:
- Replace boost pressure sensor (waiting for replacement part).

My suspicion is that the turbocharger pressure sensor was the cause of the jerky acceleration back then. What are your thoughts?

Thank you and best regards.
Mags.

Hello Mags,

Quote:

Signal height sensor/boost pressure sensor: P1592 - 006 - implausible ratio. And based on that: Vacuum leak in the intake system.

This assumption is incorrect. If the engine is running and the ignition is off, and the two sensors provide different pressure readings, then one of them is defective.

It's easy to tell which one it is, as the current air pressure can be measured using a simple "barometer." Search the internet for the current weather/air pressure for your location and compare it to the values from the two sensors.
In addition to the sensor itself, the wiring can also be faulty in a boost pressure sensor.

Best regards, Rainer.

Hello Rainer,

Thank you for the quick response. Yes, I also think that one of the sensors (a replacement part is already on its way) or the wiring is faulty, and I hope it's not the pressure sensor in the control unit.

My theory is that the two current error messages are related to the old error message (boost pressure sensor and boost pressure control).

Current error messages:
Signal altitude sensor / boost pressure sensor.
P1592 - 006: Implausible ratio.
P2279 - 006: Air leak in the intake system.

Old error message:
Boost pressure control P0299 - 006: Limit threshold exceeded.

Konkret glaube ich, dass der Ladedrucksensor bereits damals schon Mitverursacher für die Symptome (mein erster Post) war und wir das leider beim Austausch des Motors übersehen hatten. WWhat do you think?

Best regards, Mags.

Hello,

I think you should check the pressure readings displayed by both sensors, as I described.

Quote:

P2279 - 006: Leak in the intake system

Another (next) problem.

Best regards, Rainer.