I'm not sure how relevant this will be to OPs problem as it's on a different generation Volvo & model type however... I had the very same message randomly come up on my '09 XC60 D5 AWD and you won't believe what was causing it
Answer: Intermittent misfire on injector No.: 3 which turned out to be worn out / faulty injector electrical connector. I'd never have guessed that would effect the DSTC.