Some creative googling (search term "code 9016 forklift") brought me to the following website > https://forkliftcodes.com/hyster-sitdown-electric/

Search "9016" within that, you get "DTC 9016 - Forward Relay"

I've never worked on a hyster but find the electrical compartment, you should see a bunch of solenoid contacts. Have a buddy function test all the controls, and try driving forward and backward. For each control he actuates that is working correctly, you should see a contactor "pull in" and let voltage flow. It is likely that the contactor responsible for driving forward will not pull in when he tries it, and there is your problem.

The coil will have small 2 control wires supplying voltage for when the contactor is to be actuated. It will also have two or more heavy guage cables that carry the actual voltage powering the motor.

Using a voltage meter, check each control wire when your buddy tries driving it again (this part is safest to do with the drive wheels up on blocks). You should see a change in voltage when he throttles up. If you don't, your problem lies farther up the line.

If your getting control voltage but the contactor won't pull in you likley just have a bad coil. Check resistance across the coils terminals, it should be around 50 ohms.

What i've done before to kind of 'cheat' and prove it's a bad coil, is swap some parts around, find a coil in there that's the same, move the wires, just kind of experiment until you can throttle forward without the alarm. Alot of times the forward and reverse coils are the same and you can just swap wires around to test things, but bottom line, if you replace the bad coil that alarm should clear and you can drive it forward some more.