Nissan Altima 2004 2.5 S CVT Transmission 172,000 miles will not engage

Have you performed the scheduled maintenance service on the CVT? It's recommended every 60k miles. If so, Check the fluid LEVEL in the CVT. If its more than a quart low, simply adding a quart *might* resolve the problem. BE SURE TO USE NISSAN CVT FLUID!! Read your owners manual for the correct TYPE of Nissan CVT fluid. To check the fluid level, the engine must be running, and the selector in PARK. If you have never performed the scheduled CVT maintenance, and the fluid is dark yellow or brown (it should appear nearly clear on the dipstick), the fluid is spent, and has lost all lubricating properties. The CVT is likely damaged, and will probably need replacement - these CVT transmissions are not rebuildable.