96 voyager 3.0 - code 12 72 !!

96 voyager shows code 12 and then 72 ( and 55). Bought this van recently and changed plugs & pvc 3 weeks ago. The check engine light came 4 days ago. I noticed white smoke while accelerating from a stop light.( after idling for a while)... is this normal?. otherwise it is colorless.
I have to mention that I had changed the timing belt, water pump & rocker arm gasktes 2 months ago.
Could somebody tell me what could be the problem?