Q: 02 nissan altima wont reverse

Check to see if the "manual lever" on the transmission actually moves into the reverse "detent" position. You might be able to indirectly determine that by checking to see if the reverse lights come on when you select for reverse. If the manual lever (on the transmission case) is selected for reverse, and you are sure of that, and yet the car does not move in reverse, there is a fault in the valve body and/or a mechanical/hydraulic fault within the transmission. To determine the exact issue requires, at minimum, testing hydraulic pressures with external gauges (at the pressure test port) and, of course possibly disassembly to locate the faulty component(s). Even if the transmission has to be re-built, such is no big deal and so I encourage you to seek a resolution, up to and including rebuilding it yourself. If you desire a professional diagnostic and an explanation of your full slate of repair options, please use YourMechanic’s shift diagnostic service request page and the responding certified mechanic will help you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.