The thing with the zep is it is more sesitve to picking up fault codes than the standard ecu...i bet if u put the standard ecu in it will not detect a fault code.....trust me mate ive had 2 zep ecus in the past and im running one as we speak, When i had my 1st zep ecu it kept bringing up code 12 which realted to rpm signal so i put the stock ecu in and it was gone, i decided to clean up all the clips an connectors around my distributor as well cheking the connections....1 of the connections did not look so good so i had i soldered and re-installed the zep and the eml light dissapeared but this fault never came up on the stock ecu...hence the zep is more sensetive to picking up fault codes, My mate also had code 12 come up and he thinks it went away after changing his dumpvalve but it came on again after a few weeks...again it was a dodgy connection on the dizzy wiring