speedomitor and all wheel sterring not working

[idaho32z]

alright so my twin turbo 300zx is haveing problems. My speedomitor is going crazy. It randomly jumps all over the place but stabalizes when the speed is held long enough.Also the all wheel steering isnt working right. The back wheels will twich randomly at times so i have it disconected. Checked the speed sensor and its fine. Any ideas???

[A Paratroopers 300zx]

Not sure about the speedo, but the HICAS (four wheel steering) system is prone to failure. You can go ahead and delete the whole system. It's significantly cheaper than fixing it. There is a piece that is required to lock the rear end up and remove the factory hydraulic rack... it's called a HICAS eliminator bar and looks like this:

[Ace2cool]

The HICAS is actually dependent on speed. If you're not going fast enough, your HICAS will either not engage, or will output incorrect motions. That, coupled with the speedometer issue, leads me to believe that you have a failing speed sensor.

How did you go about testing it and verifying that the speed sensor works? Is your steering wheel hard to turn at low speeds or really easy to turn at high speeds? The steering resistance should feel uniform throughout any speed, as the car has speed sensitive power assist.

Also, what do you mean "have it disconnected?" Are you '94+, and have the electric HICAS as opposed to the Hydraulic? That's the only thing I can think of. That can also be dangerous, as having free back wheels will let the wheels do as they please (vibrations, ect) and the vibrations could wear and possibly break a tie rod/end link and you will have a very scary ride when the back decides it wants to go one way, and you're telling the car to go the other.

[marty1mc]

Is your cruise control working when the speedometer screws up? If not, and the combination of the other items, I would say speed sensor as well. If your cruise control is working all the time, then you probably have two different problems, speedo and HICAS.

[idaho32z]

No my cruise control insnt working. Do you know of any way to test 100% if the speed sensor works without getting a new one.

[marty1mc]

ok, it's extremely likely it's your speed sensor. But, you may not have to replace it. Go under the car, and pull down the connector, pull it apart and clean both sides of it well. Put it back together and try it again. I fixed mine that way.