Help Please Turbo Underboost After EGR Delete


Registered User
Hey all,

I have an A4 B8 2.0 tdi (CJCB) which has been experiencing many issues recently. Initially, the car went in to limp mode because of the EGR becoming blocked. After failing to attempt to clean it due to the EGR valve for this particular engine being combined with the cooler, I resorted to getting it remapped out.

So on Saturday, I went to a mapper who performed the EGR delete and mapped the vehicle to stage 1. The car was running like a dream and the power increase was just what I was looking for. However, the issues began the next morning when I left for work. I started the car, and it idled fine. I started to drive for less than a mile, and then suddenly there was a loss of power. I noticed that any slight incline would make the power loss worse. The glow plug light would flash during this. Note that I was not over revving but just holding revs around 1,000-2,000. The car stuttered and hesitated, and there was a distinctive sound similar to when an engine is cold started in extreme cold temperatures.

This issue is only present in cold start. Once the engine is warm, everything is fine. I used an OBDII adapter to find out any fault codes, and the only code that appeared was "P0299 Turbocharger/Supercharger "A" Underboost Condition". I went back to the guy who mapped my vehicle, who checked it over and suggested to reduce the power to rectify the issue. He also advised that he believes the wastegate is not opening/closing properly which is causing the issue.

I searched the realms of Google and forums to find out any resolution to the fault code. Unfortunately, I couldn't find anyone with a similar experience. Does anyone have any advice on how to diagnose what is causing the issue? Any help would be much appreciated. Thanks.

A4 B8 2.0 tdi (CJCB). Had blocked EGR valve. Performed EGR delete and remap. Car now runs fine when warm. When cold however, engine stutter and hesitation. Fault code P0299 turbo underboost.

bobby singh

VCDS Map User
Gold Supporter
Firstly there is no wastegate on these cars, they have vanes.
Sticky vanes is not so common on the common rail cars.
Was the egr valve blanked off? mapping them out is not enough sometimes.
Faulty turbo actuators is very common on the 2.0 CR engine so I would check this first.


Registered User
Hi @bobby singh ,

Thanks for the reply. No the EGR was only deleted via software and no blanking plate was installed. I did purchase a plate just in case, so I think I'll install it first to see there is any difference.

I have in fact been reading about the turbo actuators being faulty but I am unsure of a way to test them. I understand you can perform vacuum tests, but I do not have the right equipment. Is there any other method to diagnose whether the actuator requires replacing?


Registered User
UPDATE: I had time yesterday to fit a blanking plate. For my engine (CJCB), the EGR valve is combined with the cooler as one unit, and there is a pipe which runs through the back of the engine before connecting inbetween the intake manifold and throttle body. I fitted the blanking plate inbetween this pipe and the port from the engine:

Plate fitted between part 10 and part 12:

The engine now runs fine and smooth, so I assume the EGR valve although deleted is most probably stuck in an open position, therefore restricting the turbo from gaining enough pressure to boost. Hence, the underboost fault code. Thanks to @bobby singh for the suggestion!

Also, one thing to note is that for the CJCB 2.0 litre engine, the blanking plate is not the same as for the other B8 2.0 litre engines. I ended up purchasing a blanking plate for a Golf MK6 1.6 litre and that is what I fitted to my vehicle.

Hope this helps anyone who experiences this issue.