I bought a 1990 Nissan Maxima yesterday, and of course there a few things wrong with it. The main one that concerns me is the speedometer.
It’s not working right at all. Sometimes on the road it’ll sit at 0. Other times it will move, but not report the speed correctly. For example, it claimed I was doing 75 behind a funeral procession through a small town.
I had the car idling in the driveway yesterday, and noticed that the speedometer was moving. I sat there for 10 minutes, and watched as it went from 0 to 35 mph, while sitting in park.
Does anyone know what could be causing it to malfunction this way, and how to go about repairing it, or perhaps know of a better place to find out?
I only work on trucks so this might not relate. But, if the yoke on the tailshaft is loose the speedo gear can rotate or not rotate giving false readings. Tightenng the nut on the yoke will usually fix this.
This vehicle has an electronic vehicle speed sensor, not the old gear and cable type. There is a magnet inside the sensor that spins rather than a physical gear and the input goes to the speedo by wire.
Mr. Accident, does your odometer and trip set read correctly? How about cruise control, working as it should? The cruise control and the speedometer are not connected but both rely upon information from the VSS (vehicle speed sensor). If they are all acting up it may point to the VSS as the problem.
The two main possibilities are the VSS or the instrument cluster itself, but you want to find out which before you throw parts at it.
The trrucks also use a VSS which is basicaly just a pulse sensor, the pulse genertaor that I reffered to as a gear does have to rorate and if it is loose it can vibrate at idle generating a false number of pulses, or it will simply slip when traveling faster giving a false reading.
I would check for bad grounds at the instrument cluster.
I had an Altima, and the speedometer was totally whacked. I replaced the VSS, and that didn’t fix it, but smacking under the dashboard did (at least temporarily). I never got around to tearing the dash apart (I would just reset the check engine light, which this fault would set), and learned to drive without a speedo (when smacking didn’t fix it).
She didn’t mention it generating a warning light. A loose pulse wheel will not generate a light and will act exactly as the op indicated. Is also an easy quick fix or check. I have several decades experience dealing with this.
On most newer cars, the computer is smart enough to realize that erratic VSS readings like what the OP is describing aren’t normal and will throw a code. I’m not sure if that’d be the case on a Mazda of this vintage, though.
While a faulty vehicle speed sensor can certainly cause erroneous and/or erratic readings in a moving vehicle, I don’t see how it can do so when the car is sitting still, which means there is NO motion for the sensor to respond to. Look for a faulty speedometer head or instrument cluster connections.
Gary, I know you know your stuff as per a lot of your posts I have followed. On this particular issue I have witnessed it many times and in many cases found a loose tail shaft nut that holds the pulse wheel in place. It is easy and free to check and if it is not it no real money or much time has been invested. If the wheel is vibrating on the shaft when it gets into a certain position it can generate a pulse until it gets back out of that position just by vibration.
Thanks for all of the advice guys. I’ll check each suggestion until I get it fixed. Unfortunately can’t do anything today since it’s raining now, and it’ll be to dark when I get off work.
