VW T4 2.5 TDI, ACV engine, manufactured in 2001, experiencing power loss again!

Hello everyone,
The topic has been discussed here before, but unfortunately, it wasn't quite the right fit for me.

My T4 suddenly loses half of its power when going uphill and goes into limp mode.

"All the vacuum hoses have been replaced, the N75 and N18 valves are new, the mass airflow sensor has been replaced, the turbocharger has been replaced (twice!), and the sensors in the air intake manifold have been changed."

Error persists:
Sure, here's the translation of the text from German to English:

"Just so you know:"
- P1556 - Charge pressure control: Limit exceeded (too low).
sporadically
or the:
- P1557 - Charge pressure control exceeded limit.
static

Suspected cause from the workshop: The particulate filter is likely clogged and needs to be replaced.

It doesn't quite make sense to me that the check engine light is on while the car is running normally for periods of time, and then even shows a full-throttle warning. If it's supposed to be a problem, shouldn't it always indicate a lack of power, rather than just sometimes?

Do you have any ideas or know of a good VW T4 workshop near Hanover?

Best regards.
Thomas.

Hello,

Your diagnostic system is on its way. Without any values, one can only make assumptions. Have you already checked if anything is loose inside the exhaust system (muffler, catalytic converter/retrofit DPF) that could get stuck depending on the circumstances and block the exhaust?

Can you see discrepancies between the mass airflow values and the corresponding boost pressure when using VCDS?

If your AGR valve is stuck, it can prevent the build-up of boost pressure. Do you have a bypass valve on the intake manifold, and if so, is it pneumatically operated?
If so, check the status to see if it's in the "open" position. Then, as a test, disconnect the vacuum hose from the actuator cylinder of the shut-off valve and close the vacuum hose.

Best regards, Rainer.

Hello Rainer,
Values will follow as soon as VCDS is available .

Prior to the entire "operation," the original turbocharger was disassembled and rebuilt because it had been leaking oil excessively. Before that, the car had been running perfectly fine. Then, it was discovered that the rebuilt turbo wasn't working correctly, so it was removed and a "test turbo" (a used one from a vehicle with a timing belt failure) was obtained and installed as a replacement, but the same problem and error persisted!
The exhaust gas recirculation system has been disabled (a plate is inserted in the pipe leading to the exhaust). However, I can certainly try removing it and sealing it off. I'll provide an update tomorrow after my commute to work, which includes a slightly uphill section.

Thank you very much and best regards.
Thomas.

Good morning.
Yesterday, I disconnected the vacuum line, and guess what? The power is back!

What does this mean for me?
Unterdruckgehäuse der Drosselklappe undicht?

Die Entlüftung, die wie ein Benzinfilter aussieht, wurde auch schon von einer Fa. Stillgelegt.

Best regards,
Thomas.

Hi there,
referring to; with reference to; concerning; regarding
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.
Which vacuum line?
hg
Herbert.

It was the bypass valve on the intake manifold.
The hose was disconnected and sealed.
So far, after the test drive, it hasn't "gone into emergency mode" again.

Best regards.
Thomas.

It also depends on exactly where the hose was disconnected. Is there a leak behind the valve, preventing sufficient vacuum for the VTG (Variable Turbine Geometry), or is the solenoid valve for the throttle flap malfunctioning?
hg
Herbert.

Hello Herbert,
I detached the hose from the top of the valve and sealed it with a small piece of tubing. The valve was replaced with a new one three months ago.

Best regards.
Thomas.

Good morning.
Unfortunately, I'm back to zero .
Yesterday, on the way home, it ran very well at first, but then it went into limp mode (P1554).

I guess I'll have to wait for the program after all...

Best regards and have a great weekend!
Thomas.

Please check the dynamic settings for the packaging equipment at your convenience.

When the pump exits the dynamic injection start adjustment range, the engine control unit can no longer make adjustments, and the emergency mode is activated!

For me, it's always happened when I was driving in the mountains or with a fully loaded trailer (2 tons).

@Dawinchie:

Good morning.
Unfortunately, I'm not a mechanic! Can you please describe in more detail how to dynamically check the settings during the vehicle power electronics (VPE) test?
Habe mittlerweile noch die Mitteilung bekommen dass ich die Turboschläuche auf Undichtigkeiten überprüfen soll. Das Testset dafür ist gestern gekommen. Bin Excited!

Best regards.
Thomas.

It would be advisable to properly diagnose the issue using appropriate diagnostic software (e.g., VCDS) before attempting any repairs based on speculation.
P1554 is a generic OBDII code.
I understand your premium support to mean that you have access to VCDS. Could you please perform an Autoscan and post the results here?
hg
Herbert.

Unfortunately, the t4 diagnostic tool doesn't provide much information. Error: "Boost pressure below regulation limit." Therefore, a test for pressure loss is necessary.
Best regards,
Thomas

How is the bus driven?

A lot of city traffic, or also country roads/motorways, and occasionally wide open stretches?

My e-scooter also acts up sometimes when my girlfriend has been riding it for a while; it then occasionally goes into emergency mode until I manage to reset it.

It's helpful to pressure test the charge air cooler system. Also, check if the wastegate is moving freely and not stuck.

I once had a vehicle that required maintenance, and I temporarily installed a boost pressure gauge to see at what moments the emergency mode was triggered.

Jeeper-Thomas wrote:

Unfortunately, the t4 diagnostic tool doesn't provide much information. Error: Boost pressure regulation limit exceeded. Therefore, a test for pressure loss is being performed. Sincerely, Thomas

"Yes, it definitely would, you just have to want it. The engine control unit (ECU) of my old Audi 80 from 1994 also offered more than such statements suggest. And that was 6 years before your model, with a 2x2 interface. Just provide an Autoscan or, alternatively, a Screenshot of the error memory."

It doesn't seem to me that P1554 fits the description of "boost pressure regulation limit exceeded."

hg
Herbert.

Good morning, Herbert.
"Yesterday's test run showed that there wasn't enough pressure (from the turbocharger). So, I finally managed to test the system for leaks. The hoses and coolant were fine, but it was leaking directly from the shaft of what I'll call the throttle valve, located on top of the valve cover. I had another one lying around, which I installed now. Another test run is scheduled for today; yesterday it was already too late!"
Best regards,
Thomas.