I just bought a 94 accord and the speedometer wasn’t working. I read online that it was the vss so I replaced it & the plug & nothing happened. I thought maybe I had wired it wrong, so I flipped the wiring & then the check engine light came on and D4 started flashing. I switched the wiring back, and everything went back to normal but the speedometer still doesn’t work. Please help me.
also no cruise control doesn’t work

 

Does you speed sensor have a pair of hoses coming out of it? Have you electrically tested the speed sensor(old and new)? Your gauge could be out.

 

Check the connector. Seems that spilling antifreeze from the coolant hose above can harm that sensor. Intermittent problem I would think it’s the gauge

 

What could be the reason if the speedometer needle is jumping erratically and only settles at around 40 miles per hour?

 

More often than not, that's because of aged solder connections on the PCB that feeds the speedometer gauge. It's mostly a warm weather (hot day) problem, and goes away when temperature is moderate or cooler. I have a 93 that does it in summer. I'm not bothering to try to fix it by taking out the gauge and trying to resolder the weak joints. I just guess my speed based on decades of driving experience; my guesses are always right. It's even easier if there is a flow of traffic. Just fall in and run where the ones in the middle are.