speedometer / tachometer stopped working, downshifting

[formasfunction]

So yesterday when I drove to work my 94 altima (automatic) was working just fine. We had a huge rain storm, but nothing absurd, and when I got in to leave work I noticed that the speedometer and tachometer were no longer working. I figured I might have blown a fuse or something and didn't think too much about it until I got on the expressway. Now when I'm on the expressway the car will only shift into 5th while I'm excelorating otherwise it defaults to what feels like 3rd which is crazy when you're doing around 65, though I wouldn't know since my speedometer isn't working. Any ideas? HELP!

--Greg

[wonword]

I have no clue . . . but that doesnt sound too safe for you or the car.

[JustSayGo]

The speed sensor in the transmission runs the speedometer and the Reed switch that is also in the dash. The Reed switch translates the signal from the speed sensor into a signal that the transmission computer can understand. The translated message tells the transmission computer how fast the car is going. The message that the computer is receiving is that the car isn't moving, so it tells the transmission to downshift as it normally would when you are slowing down. Hopefully the rain caused a bad connection at the speed sensor connecting plug. Check the plug at the speed sensor and wiring for damage. Several people on other forums report the same condition is often intermittent. How the missing speed sensor signal effects the tachometer is unusual. I read more than one report saying the water temp gauge is also effected. If the plug and wires look good remove the speed sensor and test it. The instructions are in the Haynes Repair Manual. If you don't have a DVOM I think AutoZone will test your speed sensor after you take it out. Repairing the bad connection or replacing the sensor fixes the other gauges too.