1) Check for defective crimp connections on the main cable-harness leads between the Drive Handle Assembly and the J8 plug to the CPU Board. 2) Check for a defective CPU Board, Drive Control Board, and/or Drive Power Amplifier Board. 3) Recalibrate the Drive Handle with drive enable picked up. If the Drive Handle cannot be calibrated, replace the Drive Handle Assembly. 4) Check for a shorted diode on the brake assembly. 5) Check for defective handle-enable switch(es). 6) Check the CPU 10 V reference to the handle transducers; it may be missing or low. 7) Check for a possible tube-park latch problem (also applies to newer hall effect sensor board) 8) Check for drive-wheel problems, including drive-belt issues or foreign-material buildup on the axle. 9) Check the bumper switches for proper operation. 10) Check for worn or defective front casters. 11) Check for worn or defective motor brushes. 12) Check for a defective LVLE power supply. 13) Check R1 and R2 (dynamic brake resistors) for proper solder joints and secure connections 14) Recalibrate the drive handle 15) Check or replace bad CPU