Turbo Dean,
When the system goes nto the "display codes" mode, it lets you know what it's doing. First, it comes up P PCU, meaning it's checking codes in the powertrain control unit (PCU) computer. then it will either display the code(s) if present, followed by P Done. Next, it displays P ECU as it checks for codes in the engine control unit (ECU). Then, displays the code(s) present, then P Done again. It will then return to the odometer reading.
If all you see is P PCU, then ----------, then P Done, it meas there are no codes. Hope this helps!