What Controls the speedometer?

Hey Quick question what controls the speedometer? i notice with the ac running my speedometer is acting up its not showing the right speed, taking it sweet time going up and coming down, and it moves like if you would hold a pencil and try to make it bend by shaking it . only does this when the ac is running a soon as i turn the AC off it goes back to normal.

Quick question, what year car.

Whoops sorry left that info out it a 1994 chevy euro 3.1 with 22k miles and never mind about doing it only while ac on it did it today without it on i think it might be getting worst.

Holy crap, a 1994 with 22,000 miles?

Could be a bad cluster or VSS. VSS, or Vehicle Speed Sensor, is used to determine how fast, and how far, the car has been driven. It's essentially a small AC generator, so while it does have the possibility of going bad, I have only seen a handful come through the shop needing this part replaced.

I'm going to go with the wiring being culprit though, in my opinion. Because it's generating an electrical signal, if the wiring is trashed then you would get a bad or dirty signal on the receiving end. And a car that's been spending a lot of its life sitting around doing nothing is going to have problems...

Go to your nearest Pep Boys/Advance Auto and grab a Haynes or Chilton for your car. Excellent resource to have if you ever do any at-home work on a vehicle. Fifteen bucks is nothing compared to the cost of replacing every part you can find only to find out it was a six dollar wiring harness.

A basic scan will tell you if the pcm is recieving a signal from the speed sensor, if so, the head or wiring, if not, the sensor or wiring, this eliminates guess work.

LOL yeah it only has 22k on it bought it from an old lady in January.

i will test Vehicle Speed Sensor during the weekend. its kinda hot outside. where would i even start? how long will it take me? i have done at lot of work on my 1992 euro by myself but never wiring.

Start with a scan as I said, then where to go can be determined.

Start with a scan as I said, then where to go can be determined.

k Where to scan it? autzone? maybe there scanner will work this time since its a 94 i will pass by and see tomorrow after work

22k? holy schnikees!!!
a full scan will definately help. i went thru a ton of money before getting it done, could have saved a bundle. but then again, I drive a brand new car with 210k miles on it...

AZ cannot scan a 94 car.

well now its getting worst i guess due to the really bad heat I'm in. and you where right maxwedge AZ don't do it i forgot i thought they did 94 and up but it's 95 and up. well now this is what happen to me today after work. i started the car up drove for a bit and drop on of my co worker to his house stood outside to make a call. i had my foot on the break pedal and the car on D then the car turned off. i started it again look around on the gauges and notice it was getting hot. a soon as the fan kicked on the Volt meter dropped pass half way down and the speedometer and rpm both jumped up and came back down the car almost turned off but it recovered. i drove a bit more and came to a stop and it started to get hot again and a soon as the light turned green the fan kicked on again and i accelerated and it sort of wanted to turn of but it started to go. then i picked up my mom from the doctors office and i turned on the AC and the car started to go crazy with the gauges the rpm needle keep jumping down so i decided it to turn it off. after that every time i came to a stop the rpm needle would jumps.

Do you guys think it could be the alternator? i had a similar problem with my 1992 euro i think. the alternator does make a noise when i spin it

yes yer right, its 95 and up. my mechanic called a friend of his who works for GM, he brought the scanner they used on mine. said it runs near 7 grand. turned out to be the computer that was bad. I guess you'll have to go to the dealership and see if they will do it for you. as for the altenator, it cost me $225 to have one put in my 92 Z. I do know when they go, the bat light will stay lit, even while running. max will most likely have a better answer for that. btw max, i grew up in ny, i miss that brassy demeamor you have. people down here in the south are just too slow. noone done here gets directly "to the point"...

i think the Voltage Regulator went bad on my 92 euro and i got one but then realized it was inside the alternator so i returned it and got a new alternator because i did not have the time to open it up and change it.
Woot NY i grew up in Brooklyn move to NJ 3 years ago lol

Its usually called southern hospitality, aka manners. But more to the point of the problem...

You can take a voltmeter to the wiring for the sensor; jack the car, put the transaxle in neutral, and rotate the passenger wheel while watching the voltmeter. If you get a reasonable AC voltage, then the sensor is most likely good. Do a continuity check on the wiring, from the sensor harness to the dash connector. Finally, a continuity check on the gauge itself. Hope this helps out.

well guys i went with the feeling i had about the alternator and changed it. the alternator was black and everything around it was black like dust and the squeaking noise was worst than before. i changed it and took it for a test drive. i let it warm up and waited for the fan to kick in and when it did i had no needles jumping around or no jerking. then i tried it with the ac on and i notice no loud noise coming from the engine. i also notice more acceleration then before with and without the ac.

I could not really check the voltage regulator due to the fact that my uncles house is being taken down and that's the place i go to work on my car. i had to change the alternator in front of my house with just the few tools i had in my trunk and even better I got a nice sun burn on my neck.

Ty all who respond in my time of need you guys are great. Ive been coming to this site for the past 3 years looking for answers and always found them.

Holy crap, a 1994 with 22,000 miles?

Could be a bad cluster or VSS. VSS, or Vehicle Speed Sensor, is used to determine how fast, and how far, the car has been driven. It's essentially a small AC generator, so while it does have the possibility of going bad, I have only seen a handful come through the shop needing this part replaced.

I'm going to go with the wiring being culprit though, in my opinion. Because it's generating an electrical signal, if the wiring is trashed then you would get a bad or dirty signal on the receiving end. And a car that's been spending a lot of its life sitting around doing nothing is going to have problems...

Go to your nearest Pep Boys/Advance Auto and grab a Haynes or Chilton for your car. Excellent resource to have if you ever do any at-home work on a vehicle. Fifteen bucks is nothing compared to the cost of replacing every part you can find only to find out it was a six dollar wiring harness.

Hello-

I was having a similar issue with my 1990 Lumina where the speedometer was not showing the correct miles per hour. I tried replacing the speed sensor with a AZ part that did not fit correctly and the vehicle will now not shift out of 2nd gear and I get no miles per hour showing on the speedometer.

I since have bought an AC Delco Speed sensor that fits correctly but the car still exhibits the same no shifting and no miles per hour on the speedometer.

A mechanic at the dealer said that I should check the reluctor drive shaft gear for apple coring and that if the gear does not turn that it wont allow the signal to be transmitted to computer thus no shifting. What is your take on this problem?

I replaced the speed sensor with the correct AC Delco part and then replaced the speed sensor drive shaft, aka reluctor, condensor. I now assume it might be an electrical issue with the wiring but both the tachometer and the speedometer are showing incorrect data, mostly higher values. The vehicle shifts normally since replacing the speedometer drive shaft caused by the poorly made aftermarket, China made part that grabed the shaft. I guess I have ruled out the VSS the hard way. Now to check out the cluster and wiring. Maybe easier just to pull out a cluster and wiring harness at the bone yard!