Smoke from Exhaust only on warm days

[drkzaman]

I have 2004 XC 90. for the last 2 months I have noted that the exhaust releases alot of thick black smoke only when the day is warm and temp is over 15 C i had MOT only last wek which was Pass and also i have taken the car to one of the Local garage who says everything is fine but it only happens on warm day. can it be the diesal which i am using also the light for Engine Service required appears for few seconds to minutes now and again and disappears in few minutes.
any advice
many thanks