On January 7, 2006 company bougth a van costing $15,600 less trade-in at $5000, estimated life is 4 years, using the double declinig method I came with O book value and accumulated deprecition of $15,600 during the second year. The van was sold at $6500 at the beginning of the third year, January 9. I can't determine if there is a loss and does it continue to depreciate through the third year

DDM is twice the rate of SLM.
SLM rate is 25%, hence DDM is 50%
Cost 15,600
Year 1 7,800
Balance 7,800
Year 2 3,900
Balance 3,900
Hence gain on disposal 6,500 - 3,900 = 2,600

Your mistake was to calculate year 2 depreciation on cost instead of reduced balance as per DDM