what is the approx cost of a computer module replacement? engine code p0604

I would be positive before replacing the computer often people jump to that conclusion. Not sure how far their information goes back but Kia as a car manufacturer put a lot of great technical information and work shop manuals on line for free for Kia owners. www.kiatechinfo.com I would check that the computer has good grounds and good power supplies. Check system charging voltage and output pattern to make sure it is not a charging system problem. ECM replacement is only .6 hour cost of ECU from Kia is $750. Call Fuel Injection Corporation in Livermore CA, or look on line at www.rockauto.com or just Google an ECU for your vehicle.