Catalysis of the reaction: abieta-7,13-dien-18-ol + NADPH + H+ + O2 = abieta-7,13-dien-18-al + NADP+ + 2 H2O. This is a two step reaction. The first step is: abieta-7,13-dien-18-ol + NADPH + H+ + O2 = abieta-7,13-dien-18,18-diol + + NADP+ + H2O. The second step is a spontaneous reaction: abieta-7,13-dien-18,18-diol = abieta-7,13-dien-18-al + H2O.