1996 Nissan Maxima GXE Fail Smog Check Due To ECM System Failure

Your Nissan Dealer doesnt want to fix your car.
There are several vehicles in history that have extreme issues running monitors. 96-98 Hyundai and Mitsubishi cars among them.
The Smog test has addendums that exempt problem cars from monitors. If you have a car that is NOT on the list, and your mechanic cannot fix it, he isnt trying hard enough or isnt very good at his job.
NOW, there are several known issues that prevent monitors on pre-2002 vehicles that some technicians do not think of or know about. FUEL LEVEL is important. Not just what your gauge shows, but what the Engine Modules internal "gauge" shows. It uses the same sender as your instrument gauge, but it must read OVER 5% fuel to enable monitors on most vehicles, and over 10# to enable evap on most cars (misfire o2 and cat will often work up to 5% and at 5 or lower they suspend). Computed fuel level should be checked and will often never set a code. AIR TEMP and FUEL TEMP are both critical. If very far off they will code, but if only slightly off low or high, they can suspend monitors.
GEAR POSITION has been known to suspend monitors and not code on some vehicles. Some vehicles may shift, but the gear position shows 2nd gear when in drive. The computer suspends monitors in low gears.
MEMORY POWER is crucial. Many cars have a memory power circuit to the ECU, and if it blows its fuse, the car will run, but has no storage memory for codes or monitors. Its running them, but you will never see it because it erases every key cycle since the power for the memory is missing.

These are but a few. There are many many small detail items that can also play in (invalid vhicle speed sense, ABS issues on some cars, incorrect components installed) that allow cars to run and set no codes and not actually run right or perform monitors.

Try a different Dealership or seek out an independent nissan specialist who is smog certified...preferably one who can claim MASTER status, and likely the problem can be solved.

Working on one right now and hooked it up with a Snap On Solus scanner - It gives P0135 for 0/2 sensor bank 1 sensor 1. Check the 0/'2 sensor function and replace as necessary

There is no way to fix this issue according to my Nissan Dealer Service Manager. The monitors will not run and therefore the vehicle will not pass smog. If you need assistance from California's SMOG authority they are called "The Referee" and you can call them at 1-800-622-7733.