D24T getting persistent overboost?

[armalite]

Hi all, newbie here so hope this isn't a dumb question.

I've got a d24T 740 auto that I've had for about 2 years. It's always been fine, but recently the turbo seems to overboosting where it never used to. Up till about 3 months back I'd get no more than about 9lbs even at max revs/throttle (5k r/min) and the overboost light never came on. Suddenly, for no apparent reason (I've not done anything) the boost started climbing all the way to 15lbs as I rev'd up (and always when I use the kickdown), the bypass valve cuts in (you can hear it) dropping the boost to about 5lbs and the turbo warning light comes on. Apart from making overtaking very 'interesting', I'm worried that I may blow something up. The car certainly doesn't seem any quicker than before, and is a lot slower once the bypass comes in, so I'm confused.

Can anyone help?

Thanks in advance,

Adman.

[Kmaniac in California USA]

Sounds like the wastegate on your turbo has ceased to function. The wastegate is a pressure regulating device that prevents overboost. I am not familar with Volvo turbo's but I do have another brand car with a turbo. The wastegate is either vacuum or mechanically operated. Read up on your specific system and check it out.