Howo Mining Truck Cargo Box Fails to Lift – Causes & Troubleshooting
The failure of the cargo box of Howo off-highway mining truck to lift mainly falls into four categories: operation error, pneumatic/electrical fault, hydraulic system failure, and mechanical & working condition abnormality. Different from ordinary dump trucks, Howo mining trucks mostly adopt a power take-off (PTO) + hydraulic lifting system controlled by air. The faults have distinctive characteristics. Below are the detailed causes, fault symptoms and simple troubleshooting methods:
1. Incorrect Operation Settings (Most Common & Easily Overlooked)
Most minor lifting faults are not caused by vehicle damage but non-standard operating procedures. The lifting operation of Howo mining trucks follows a specific logic. Improper operation will directly result in no lifting movement.
Power Take-off (PTO) not engaged properly: No gear shift is required for lifting on Howo mining trucks. Start the engine and press the PTO switch in the cab. The PTO indicator light on the dashboard must turn on to connect power. If the PTO is not switched on or the switch has poor contact, the hydraulic pump will not work and the cargo box will have no lifting response at all.
Improper position of the control handle: The lifting handle is not pushed to the lifting position, staying in neutral or lowering position. A stuck or misaligned handle fails to trigger the hydraulic oil circuit reversing, so no lifting power is output.
Operation under invalid working conditions: Overloading, uneven cargo stacking, or parking on steep/inclined ground. The hydraulic system exceeds its load limit and cannot build enough pressure to lift the box. The built-in protection lock prohibits lifting if you attempt to operate the lifting function while driving.
2. Pneumatic and Electrical Faults (Power Switching Failure)
The lifting system of Howo mining truck relies on air pressure to control PTO engagement and hydraulic valve reversing. Faults in air and electric circuits will directly cut off the control signal for lifting, with no lifting action.
Insufficient air pressure of the system: When the air pressure of the air reservoir is lower than 0.6 MPa, the pneumatic control valve cannot open. The PTO cylinder fails to engage the PTO gear. Common causes: insufficient air supply from the air compressor, accumulated water/ice in the air reservoir, cracked/leaking air pipes, blocked or squeezed pipelines. Frozen pipe blockage often occurs in winter.
Faults of switches and wiring: Damaged PTO switch, blown fuse, loose or broken wires. The PTO solenoid valve has no power supply and cannot work. Malfunction of lifting limit switch and safety interlock switch makes the system misjudge working conditions and activate protection to block lifting.
Stuck pneumatic control valve: The spool of the pneumatic control valve is stuck or its seal fails. It cannot switch air and hydraulic signals. Even if air pressure and electric circuit are normal, the hydraulic system cannot receive the lifting command.
3. Hydraulic System Faults (Core Power Fault, High Incidence)
The hydraulic system is the core of lifting. Abnormalities in hydraulic oil, oil pump, valve assembly or oil cylinder will lead to no pressure or insufficient pressure, resulting in lifting failure, which can be divided into two types: no lifting at all and weak lifting force.
Abnormal hydraulic oil: Too low oil level in the hydraulic tank causes the system to suck air and build no pressure. Deteriorated hydraulic oil, improper viscosity, water emulsification cannot form effective oil pressure. Excessive impurities in oil block pipelines and filter elements.
Blockage and leakage in oil circuit: Severe blockage of suction filter and return filter of the hydraulic tank hinders oil circulation. Cracked hydraulic pipelines, loose joints and aging sealing rings cause serious internal and external leakage. System pressure keeps losing and cannot support lifting.
Hydraulic pump failure: If PTO is engaged normally but the pump generates no pressure, it is usually caused by pump wear, damaged gear or pump body failure so the pump cannot deliver hydraulic oil. Poor sealing of the pump inlet pipe sucks a large amount of air, leading to unstable system pressure and no lifting force.
Faults of valve assembly and oil cylinder: Stuck or worn reversing valve, check valve and overflow valve spool cause pressure relief and pressure cannot be maintained. Aging and damaged oil seals of the lifting cylinder produce internal oil leakage inside the cylinder. The cylinder has oil cross-flow; it may move slightly under no load but cannot lift under full load. If the setting pressure of the overflow valve is too low, the system releases pressure in advance and fails to reach the required lifting pressure.
4. Mechanical Transmission and Structural Faults
Abnormal engagement of PTO: Worn PTO gear, incomplete engagement, unbalanced shim thickness. Power cannot be transmitted to the hydraulic pump and the pump idles without power. Damaged or stuck PTO bearing makes the oil pump unable to rotate.
Mechanical jamming and deformation: Rust and lack of lubrication at the hinge points of the cargo box cause jamming. Deformation and sticking of lifting cylinders and brackets create excessive mechanical resistance exceeding the load capacity of the hydraulic system. Misaligned and stuck cargo box limit devices block the lifting movement.