The error code relates to the pump driver circuit and is relatively simple to fix.

Have you contacted a local Cat Lift Truck dealer for assitance?

The below is the brief overview of the problem, but unless you now what and how to test the components detailed it is not something you can do yourself.

Possible Cause: D4P (Diode) Shorted, Driver board defect, Logic Defect, Faulty Wiring, Poor Connection at P12-3 and/or P12-7; Poor connection of wire 79 and/or 80 to R322.

The above is self explanitory to anyone who has any sort of experience, but I guess it will not mean much to you.