this truck is equipped with a lift limit switch it is a proximity switch mounted close to the lift motor pointing at the links on top of the lift cylinders, if it goes bad and gets stuck closed your not going to lift. there is an indicator light on it to show you when it is closed (lift disabled) unfortunatley the light being off will not guarantee the switch is good.

someone might be able to correct me if i am wrong but i am sure if you un-plug the switch the truck will still let you lift, so unplug it. if you now lift replace the lift limit switch.

the hpd code you are seeing is unrelated to the no lift problem, you may have turned the key on with the handle down.