I have a 1996 Nissan 240SX SE, I've been having the check engine light P0500 for a long time, I was told its not my speed sensor since my speedometer works. Also the error code P1445 my EVAP volume pu

It won't pass smog in California because the 1st thing a smog tech does it check for fault codes on the vehicle's computer with a scanner.

link with some info about faulty speedometer.
https://wheelzine.com/speedometer-not-working-properly

https://maxima.org/forums/4th-generation-maxima-1995-1999/311797-fixing-speedometer-odometer-work-sporadically.html

This may not be of any help but I had a 94 and the speedometer kept messing up. One day my wife was in it and she was stopped at a red light and it was bouncing around 30 MPH. She took it to the dealer we bought it from. They told me it is run off electrical signal and the alternator was bad. They changed the alternator and we never had the problem again. Just a thought check your alternator see if voltage is good are bouncing around. You can check it at the battery while it is running. I have never heard of anyone else where the alternator effected the speedometer but it is what I was told and they did change the alternator.
I will say I do not remember the MPH being 0 while running.

fault code is p0500
symptoms
loss of anti-lock brakes the "anti-lock" or "brake" warning lamps on the dash may be lit the speedometer or odometer may not work properly (or at all) your vehicle's RPM limiter may be decreased the shifting of an automatic transmission may become erratic other symptoms may also be present

Read more at: https://www.obd-codes.com/p0500
Copyright OBD-Codes.com

if the engine check light is on
the engine computer has fault codes to be read

this is the speed sensor on a 2003 nissan frontier

According to http://repairpal.com/OBD-II-Code-P0500:

Vehicle Speed Sensor Malfunction
Symptoms

• Check Engine Light will illuminate
• Vehicle may not shift properly
• Speedometer may not operate correctly
• In some cases, there are no adverse conditions noticed by the driver
• In some cases, there may be performance problems and/or shifting problems.
• Other warning lights may come on such as the ABS light and Traction Control light.

Common Problems That Trigger the P0500 Code

• Defective Vehicle Speed Sensor
• Defective Speedometer
• Vehicle Speed Sensor wiring or connector
• Communication (CAN) bus problems
• Defective transmission or differential Vehicle Speed Sensor drive gear

Common Misdiagnoses

• Speedomter problem
• Internal Transmission problem
• ABS/Traction Control probelm
• Driveline problem

You could have a faulty speedometer/odometer combination meter causing a false Vehicle Speed Sensor error.
My 1998 Sienna had the following symptoms:
- Speedometer and odometer failed intermittently
- The check engine light would come on and I would get a p0500 code in the OBDII.
- The cruise control would stop working at the same time the speedometer failed.
There is a speed sensor in each one of the tires and they feed the speed information to the ABS ECU. From the ABS ECU the speed signal goes to the speedometer/odometer combination meter, and from there it goes to the Engine Control Module and to the Cruise Control ECU. I could see a signal coming into the speedometer/odometer, but no signal going out. Replacing the speedometer/odometer combination meter fixed the problem.

you'll need a systems check to see which speed sensor is acting up they can be intermittant

I too be live first thing to check oxygen sensor, possibly fuel filter . Hope this helps some.

you need a new speedo head/speedometer assembly

Firstly, the code p1445 is actually an EVAP Canister Purge Control Valve...The most common problem is a failure of the valve itself, which is located at the top of the plenum chamber. Nissan offers a replacement valve with new bracket and hoses. It is around the $150-$200.00 mark.

But, remember to test the component (valve) first as this suggestion is just to the common problem, but in rare cases, it might be PCM related (water entry, shock etc)

Secondly, the p0500 code is a speed sensor and you can pick these up from autozone.....it provides the road speed for the speedometer and odometer..........if these are working fine, then you might have a wiring issue.

As these are 2 seperate systems, I doubt that they are related.

I hope this helps

yes your ecm is going or i could even be the computer nissan is a good car but it will be expensive to fix