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2009 VW Caddy Van 1.9 PDf – Lack of Power.

This vehicle was in for a number of items, one of them being a lack of power noticed when coming off the motorway, slowing down but then no power when back on the accelerator. After a code read we found a low boost pressure fault P0229 boost regulation. The customer had some knowledge of these vehicles having problems with the variable vanes in the turbo, this is where i’d have looked anyway with this fault, because it was easy to test I did this first. Vanes were free and turbo held the vacuum. I then road tested with the diagnostic reading the boost pressure data, on boost gets up to 2200 mbar which was expected on a good example. Happy that the turbo and vanes were operating correctly I checked for boost leaks, I used the smoke tester in the intake, no leaks present. Thinking to myself what could affect boost pressure I looked along the lines of vacuum control for the turbo. From the turbo actuator to the turbo held vacuum, so I checked the vacuum at the actuator, it seemed pretty good at first glance.

With the fault occurrence in mind I depressed the brake pedal a couple of times, the pressure then dropped and took a few seconds to stabilise:

At this point I’d invested a little too much time into this fault, so before I went any further I secured another hour diagnosis to play with. I explained I thought there was a vacuum supply issue and either there was a leak or the vacuum pump wasn’t supplying sufficient vacuum. The fault occurs when slowing because the brake servo is using all of the vacuum so when the turbo requests boost straight after braking it can’t ‘pull’ enough vacuum thus under boosting the turbo.

I smoke tested the vacuum system. There was an obvious leak from the breather in the cam cover along a seam. For this test we used a smoke tester which allows us to carry out incredibly accurate leak tests on turbo systems enabling fast and efficient diagnostics.

To prove this was the fault I removed the feed pipe and blanked it off and re checked the vacuum at the turbo actuator. The difference was obvious, vacuum was instant.

We have had authorisation to replace the cam cover and will confirm the repair once it has been done.

Very happy with the diagnosis on this, could have easily been overlooked as the fault wasn’t present on road test, shows the thought process and elimination work. I look forward to showing and explaining the customer as he is quite mechanically minded and interested in the fault.

It’s these sort of jobs we absolutely love getting to the bottom of as it breaks the mould and proves that a good diagnostic process is essential to accurate diagnosing and repairing cars.

Here at Cheltenham and Gloucester Autocentre we pride ourselves in good Diagnostics process and have invested heavily not only expert diagnostic training but in specialist diagnostic equipment enabling us to accurately diagnose and repair your car getting you back on the road with the piece of mind the job as been done properly.