VW T4 AJT: No Power? Troubleshooting Guide

Hello, I have a T4 2.5 TDI AJT, and recently it has almost no power (it feels like it's running as an naturally aspirated engine). I've already replaced all the vacuum hoses leading to the N75 valve, but it didn't help. According to VCDS, it's not reaching the target boost pressure. If anyone has any ideas about what the problem might be, please let me know. Thanks, Chrisi.

Hello Chrissi,

Welcome. What error code is stored?
Would you like to upload a scan for us to see?


Based on the information we have so far, we can only guess...


Does the intercooler work?
Is the intake system contaminated with oil sludge?
Is the turbocharger okay?
Do the pressure hoses have any cracks?
and so on and so forth...

The self-study articles are highly recommended...

The more information you provide, the more likely it is that someone here will be able to help you.

Best regards,

Michael.

Hello,
No error code is displayed.
I've checked almost everything (replaced the intake manifold, boost hoses, vacuum hoses, the turbo has very little play, etc.).
"However, the turbocharger only builds up approximately 0.4 bar of boost pressure, while the target pressure should be 0.6 bar. The pressure sensor is not being activated, and I've connected a pressure gauge to the line leading to the pressure sensor, which shows no pressure. Normally, at 0.6 bar, there should be enough pressure to open the wastegate and regulate the boost pressure, but it's not reaching that level."
Best regards,
Chrisi

Hello Chrissi,

Have you checked the N75 solenoid valve? Is the resistance value within the range of 25-45 ohms? Is the valve working properly, or is it possibly stuck?

Did you check the wastegate valve using a vacuum pump?

Is the linkage moving freely? Or, is the linkage obstructed?


Best regards,

Michael.

Is the hose in the MSG (Manifold Absolute Pressure sensor) connected to the turbocharger pressure sensor in good condition, if it is installed there?

Chrisi60 wrote:

Hallo, Ich habe einen T4 2,5tdi AJT 2,5tdi, der seit kurzem fast keine Leistung mehr hat(fährt sich wie ein Sauger). Ich habe erstmals alle Unterdruckschläuche die zum n75 führen erneuert, hat aber nichts gebracht. Laut VCDS erreicht er den Soll- Ladedruck nicht. Wenn jemand eine Idee hat was das Problem sein könnte bitte antworten. Mfg. Chrisi

Is there a troubleshooting guide for performance issues? Is this always displayed while someone is new here, unless they specifically click it away?