Dpf might need replacing if the cleaning doesn't work.
Regarding the power steering, how old is the car battery? I ask because if it's over 5-7 years old then it could be failing. This can cause the car to throw up all sorts of electrical issues.
I'd recommend a diagnostic check to see if any fault codes flag up.
If you've bought it from a dealer then they have to fix it foc in the first 30 days from sale as you're still entitled to a full refund within that time.
Get it back to the supplying dealer for them to sort. It should be free of charge if you live in the UK as under consumer you have 30 days for a full refund.