Catalysis of the reactions: a 4,5-saturated-(2E)-enoyl-CoA + NADP+ = a (2E,4E)-dienoyl-CoA + H+ + NADPH, and a (2E,4Z)-dienoyl-CoA + H+ + NADPH = a 4,5-saturated-(2E)-enoyl-CoA + NADP+.
4-enoyl coenzyme A (reduced nicotinamide adenine dinucleotide phosphate) reductase activity