Failure Discription：The display always shows the height limit alarm, the large and small hooks cannot be raised and the boom cannot be lowered.
Failure Analyce & Trouble shooting：1.The height limiter is damaged.
2.The SYMC controller on the bus is damaged.
3.The line from the height limiter to the control is open.
4.The cable reel is damaged.
2.After wiring directly from the height limiter to the input terminal of the onboard SYMC controller, check that all actions are normal and the alarm disappears. It can be judged that the controller is normal.
3.Checked that the connectors from the height limiter to the control circuit are connected properly. Open the cable reel and check that the conductive ring inside the circuit board is loose. Occasionally, the conductive ring works normally when you move the conductive ring by hand. The conductive ring inside the barrel is damaged, and this failure can be solved after replacing the cable reel assembly. 

Principle & Expierence Summary：For this kind of fault, you need to be familiar with the direction of the height limiter circuit, and then eliminate the fault location of the line in sections