From memory A04 is an anomaly in the manual, I think it says shunt wires on wrong way round but unless you have removed them in the first place then this cannot be the case.
What it normally is is bad connections on the multi plug on the controller, the pins are aluminium and the contacts in the plug are metal so you get a very thin layer of corrosion as they are dissimilar materials, you may not even be able to see it.
The best thing to do is remove the plug (make sure you disconnect the battery as it can blow the controller if still powered up) spray contact cleaner on the pins and in the plug and push in and out multiple times to clean off corrosion, then blow out with air, re connect and give it a try, came across this loads of times on LE , KE and JE Boss machines with Bosch LT controllers, not saying that its this 100% but worth checking.

can i please know what A04 is too please?
[email address removed]
many thanks

Hi, if you can help me, I am working on forklift Boss LE18HV and have following error code AR04. Thank you in advance!
Edit

mark, thanks for replying we will check it out

HELLO PETER, COULD IT BE THAT THERE ARE 3 CONTROLLERS MP1514? IF SO ERROR CODE 035 IS A PROBLEM WITH THE ACCELERATOR (NO ZERO POSTION)
REGARDS
MARCB