I have a 1994 Honda Civic DX that is having a problem with either its
speedometer or some other part of its speed sensing circuit. The
speedometer shows speeds all over its gauge (and sometimes has even
pointed straight down). When it does move (and it doesn't always while
I am driving) the motion is not smooth but jittery. Sometimes it will
jump up and show I'm doing 100 or more mph but seeing as I'm the
slowest car on the road at the time I know the reading isn't even
close. I can set the cruise control and it will keep the car at an even
speed. When cruise is engaged the speedometer will sometimes hover
around a constant reading (which I can tell by the flow of traffic
isn't correct but the reading is more or less stable) but other times
the speedometer will fluctuate by 15 or more mph. I replaced the speed
sensor because most people I talked to (even the Honda dealership) said
that was most likely the source of the problem. When I took the old
speed sensor off it was filthy inside with what looked like some kind
of grease. When the new speed sensor went on the problem seemed to
disappear but by the next day the speedometer was back to being
erratic. I don't know if the new speed sensor fixed the problem
temporarily or I was just lucky. I can't even be sure it was accurate
during this time but it wasn't erratic like it often was before and is
again. I also haven't opened up the replacement speed sensor to see if
it is now filled with that thick "grease" too. Since I replaced the
speed sensor and the problem remains I am looking for some other ideas
before I change out more components. Yes, it could be a speed head gone
bad but are there any other possibilities that I should check out
before getting a replacement speed head. Everyone swore it was the
speed sensor so I replaced it but it would seem they were all wrong and
I would prefer not to just blindly continue replacing components.