Straight limit is when the order picker is up in the air past the third height switch. Your height switch has probably failed in the open position which is telling the machine it is up in the air. You're 3400 probably has height switches instead of a height encoder cable reel if it's still going up all the way. If you had a cable reel encoder and the cable broke or encoder failed the truck would only lift 36" then stop and code out.

For example, my SP's max height is 240", once they pass 218" the display shows STR LIMIT which means the third height switch has been released.

This limits the movement of the truck above 218", it will only move forward or reverse when the drive unit is directly for/aft.

There is no steer limit sensor on the 3400's only steer encoders, the tiller wheel encoder (steering wheel) and the steer feedback encoder(mounted infront of the drive motor on the motor baseplate this has a spur gear attached to the main steering gear which is how the encoder gets turned).

The steering feedback encoder is the one that always gives problems. You will need a handset to plug into the machine to set the position on the steering feedback encoder. The drive unit must be aligned for/aft via a line groved into the baseplate and the drive units transmission. Then the encoder must be set to I0 (center), the encoder goes to +800 or in the other direction -800 for left and right. If your drive unit is facing for/aft and the handset displays anything other than +1, I0, -1 then it is out of range. If you turn the encoder and the number doesn't change the encoder is bad.