Alright... I need some help, I'm clueless at this point... Here's the deal:

For a long time now, my speedometer has been bouncing around. 6 months ago, it would occasionally just lag at 0 for awhile before jumping up to the right speed. A couple months later, it still did that, and also started 'ticking' down a little every ocuple of seconds, so like bouncing... Now, things are far worse, it rarely ever even indicates a speed, and when it does, it just continuously bounces to the point that I have no idea what speed i'm going. Also, the Trip/Odometer don't count up when its stuck at 0 (so this makes me think its not the meter itself thats broken, but the signal going to it, since all 3 functions exhibit similar performance.)

I like trying to figure out how things work, and I don't like askin for help unless I need it, so this is what I've tried. My dad mentioned something about a loose speedometer cable... after attempting to remove mine to check, I realized that i don't have one (I don't think) My entire instrument cluster is electronic, the only connections into it is a little socket behind the cluster. So after more research, the cable is only on manual transmissions I think... So anyways, I'm ptretty sure I have a 'speed sensor' and its all just wires between... is that right? And if so, how does the speed sensor work? could it fail intermittently like this? Also, I looked at how much a new speed sensor would cost, and there's like 8 or 9 different options... I have no idea which one I need.

So, what I'm asking is... could the speed sensor be the problem? Is it likely the problem? And if so, where is it located, and how do I get it out? And one last thing, the socket/connections are pretty nastily gunked up, could that be causing it? Its only 3 of the pins, and it doesn't look bad enough to limit any current flow.

Thanks!

 

You are right, your car does not have a mechanical cable to drive the speedo.

I am having the same problem and from what I can gather there are two possible problems. First, the VSS (vehicle speed sensor) which bolts into the side of your tranny may be defective and not sending a signal to the speedo. Then there is another device associated with electronic speedos which could be at fault. I don't have much info on this piece. My ECM is throwing a VSS code but I haven't tracked down the problem yet.

 

Hmmm... I fixed my problem, I never had a code though, it just wouldn't work. In the '90, the VSS is just a permanent magnet generator which is spun by the gear in the back of the trans, and sends its generated AC signal straight to the ECM via 2 wires (purple/yellow), the ECM does what it will with it (I believe the code means its not connected properly (lack of input) or the ECM itself is jacked, and not doing its AC-DC conversion properly or something..

Anyways, the DC is used for quite a few things I think, but most importantly, the speedometer/odometer/trip are driven by a DC voltage proportional to speed... However, if all thats wrong is the that shaft of the VSS isn't spinning because the bearing gave out, causing enough play so the VSS gear won't engage the driveshaft gear, you don't get any code. All I had to do was take out my VSS and wiggle the shaft, its was obviously wobbly so I replaced it, and presto. Sounds like you may have a more serious problem. Might wanna have your ECM tested or something.