ASE Practice Test (E1: Truck Equipment Installation & Repair) 3

Question 1

What does GVWR stand for, and why is it critical when upfitting a commercial truck?

Accepted Answer

Gross Vehicle Weight Rating — the maximum permissible loaded weight of the vehicle including the truck, body, equipment, cargo, and passengers

Answer

GVWR (Gross Vehicle Weight Rating) is the maximum safe operational weight of a fully loaded vehicle as rated by the manufacturer. When upfitting, the weight of the body, equipment, tools, and cargo plus the base vehicle weight must not exceed the GVWR. Exceeding GVWR is illegal (overweight violations), unsafe (reduced braking, structural overload), and voids warranty. Upfitters must calculate the curb weight plus the upfit weight to determine available payload capacity.

Question 2

A crane mounted on a truck body develops hydraulic drift (the crane boom slowly lowers when the control valve is in the neutral position). What component is MOST likely causing this?

Accepted Answer

Internal leakage past the control valve spool or cylinder piston seals

Answer

Hydraulic drift occurs when pressurized fluid bypasses the load-holding mechanism and returns to the reservoir or opposite side of the cylinder. In the neutral position, the control valve should block all fluid flow. Internal leakage past a worn or contaminated control valve spool, or past the cylinder piston seal, allows the load to push the cylinder down slowly. A counterbalance valve or load check valve, if present and malfunctioning, can also cause drift.

Question 3

When installing a flat-bed body on a pickup or cab-chassis, what must be done to ensure the body is level?

Accepted Answer

Shim the body mounting locations to achieve a level flatbed, measuring both side-to-side and front-to-back with a precision level

Answer

Truck frame rails are not always perfectly level side-to-side or front-to-back due to manufacturing tolerances and frame design. Shimming body mounting blocks adjusts the height at each mounting point to achieve a level flatbed surface. A precision level placed at multiple locations on the bed confirms levelness. This is important for load containment, tail-lift operation, and professional appearance. An unlevel flatbed can cause cargo shifts during transport.

Question 4

What is the purpose of a multiplexed wiring system (CAN bus or SAE J1939) in a modern commercial upfitted truck?

Accepted Answer

To allow multiple electronic modules and body equipment to communicate over a shared data network using low-current signal wires, reducing wiring complexity

Answer

Modern commercial trucks use CAN bus (J1939 for heavy trucks) multiplexed wiring. Instead of a separate wire for every function, multiple modules share a two-wire data bus and communicate digitally. Body builders and upfitters must interface their equipment through the truck's body builder module or via approved connections to this bus. Improper CAN bus interference can disable critical vehicle systems including ABS, engine control, and instrument clusters.

Question 5

A telescoping aerial lift on a utility truck will not extend beyond a certain point and has a warning light on the control panel. What should the technician check FIRST?

Accepted Answer

Check the load moment indicator (LMI) or overload sensor system — the lift may be preventing extension due to a sensed overload condition

Answer

Aerial lifts and cranes are equipped with load moment indicators (LMI) or overload protection systems that prevent operation beyond rated capacity. If the system senses that extending further would exceed the rated load moment (load × radius), it locks out further extension and activates a warning. The technician must verify the load, boom angle, and extension against the load chart. If not overloaded, the LMI sensor or system itself may require calibration or diagnosis.