TealCivic115

I replaced my heater core and cleaned up a few things behind my dash and come to find that my speedo doesnt work when i finished, or it jumps all over the place while driving. worked great before, but now this. I have a good feeling that its the connection, because it wiggles a little when i plug it in. My guess was that my hasport motor mounts are causing it to vibrate so much, because when i rev it up to about 4,500-5,500 RPM, it flutters to differing speeds. Even while im completely stopped, or moving. I also disconnected the yellow SRS plug because the red SRS dash light would stay on for some reason. (pretty sure it does not need to be plugged in for speedo operation, but not 100 % sure.

Any input would help for this situation because safety is a concern.

Thanks HT

TealCivic115

has anybody ran into this issue or something similar? possibly the mounts too, or transmission speed sensor?

Thanks HT

dem0nk1d

i have changed out the circuit behind the cluster and fixed the issue.

Hasport

the mounts arent the cause of the problem

its 1 of 3 things

speedo itself went bad
speed sensor went bad
connection at the speed sensor is bad

TealCivic115

I was guessing that it was the mounts due to the poor connection between the sensor and the plug. I pulled it out yesterday and noticed some of the plastic guides in the plug were broken and therefore the middle pins (male and female) were not making direct contact with each other. And thought that they did make contact, but very few times when the motor was revving higher, possibly causing vibration. Anyways I found it to be the plug and sensor connection. Must have gotten bumped while removing the heater core nipple hoses.

kaiana

OK. This is fairly simple.

There are only 4 things that can cause speedo problems. (After checking fuses)

Faulty Speed Sensor
Faulty Speedo Head
Dead short on the wiring harness
Poor earth.

So first you must start with the obvious. Remove the speedo cluster. Leave it connected to the wiring. Car jacked up un stands, running in 1st gear. With a multimeter place the black lead on the screw head on the rear of the cluster marked "-" Place the red lead on the screw marked "SP" (Speed Pulse) you should receive a voltage pulse.

If yes
then your problem is with the speedometer. dis-assemble the speed cluster and remove the speedometer by removing the 3 screws. Unclip the circuit board from the rear. Now re-solder every solder joint. 99% of all faulty speedos are caused by dry solder joints.

If no
The next most common cause of the problem is poor earth. Usually this is cause because one or all 3 of the earth leads located on the inlet manifold behind the distributor is loose, Not screwed on at all or broken.

It is also common that the wiring harness (Alternator harness) rubs through the insulation and causes a dead short. This can be checked by moving the harness whilst watching the speedo.

The last place to check is the speed sensor located on the Gearbox. These are usually the first thing people replace and is rarely the problem. If these are good go back to the If yes above.

Final note. The speedo is a closed circuit system. It does not rely on the CPU for pulse. The pulse drives the odometer and the speedo. (Not the Taco) If either the Odometer or the speedo work and the other does not the problem is the speedometer. If you have no taco, no speedo, and no odometer......Check your fuses.

Former User

Decomposed thread closed.