Problems with Speedometer, 1996 Civic EX AT. PLEASE HELP!!?

Question

Hi,

I drive a 1996 Honda Civic Ex. Auto Trans. Huge problem, the speedometer keeps jumping from 0-120mph and sometimes it doesn't even work. Also, the cars lights and power seems to fluctuate at the first 5 minutes of running.

I have replaced the battery and the alternator and I'm hoping its not something big. I don't want to replace the VSS, trans, or the gauge cluster but... I'm probably going to get pulled over really soon without a proper mph gauge.. PLEASE HELP!!

Thanks,

Tony

Answer 1

the speedometer is not cable driven; it works off of an electrical sensor called a vehicle speed sensor that is mounted on the transmission.  if that signal is erratic then your speedometer needle will jump.  you need to replace the vehicle speed sensor to repair the speedometer problem in 99% of the cases.

As for the lights, the flickering or dimming happens when the battery is supplying most of the current for the electrical load instead of the alternator

Since the early ’90s, Honda vehicles have come with an electrical load detector (ELD) unit in the under-hood fuse/relay box. This unit allows the ECM/PCM to regulate the alternator (switch it between high output and low output) to provide the best combination of fuel economy and electrical system operation. The ELD sends a signal to the ECM/PCM that’s proportional to the electrical demand. The ECM/PCM switches the alternator between high output and low output depending on several factors, which include electrical demand, battery charge level, and the driving cycle. When the alternator is in low output, the engine load is reduced and fuel economy improves.

If the battery and alternator belt are okay, chances are the flickering or dimming isn’t an electrical problem but rather the switching altrnator output due to the operation of the ELD.

typically if the ELD goes "bad" there is a code that sets in the onboard diagnostic system and the check engine light is illuminated.  if that's not the case, the ELD is probably working as designed.

be sure the alternator belt is properly adjusted as that will affect output even though the alternator and battery are new a misadjsuted belt will cause a low output.

hope that helps

Answer 2

Sound like two problems. First, the speedometer, sound like a dirty cable. Remove the cable end from the dash board side a spray some cleaner in it, even WD 40 will work, not a lot, just enough to lube the dry cable. You can also drive with the cable unattached and have a friend ride and look at the cable, see if it turns smoothly or jumps and jerks. May need to replace the cable. Can also be the gear in the transmission or the speedometer itself. The cable is the easiest and least costly fix and you can diagnose that yourself. The other problem is electrical, most likely the alternator or voltage regulator. Both you can replace...alternator is more expensive than regulator, and regulator is usually easier to change. Both can be affected by heat, after car warms up, the regulator can intermittently fail. Have had this problem in the past and both times (two different cars) it was the regulator. Usually a simple and cost effective fix.  

Answer 3

Tony, even if  you have sent this question to the best technician in the world, he would ask you to bring the car in so he could see it. So take it to a specialist and relax.