Intermittent Speedometer/odometer: 91 318is

[erik the red]

Symptoms:
1. Speedometer suddenly drops to zero, and the odometer stops working. Sometimes it just stops without warning, sometimes after I hit a bump. Usually happens when the air temperature is below 60 degrees or so. When the car's been sitting in the sun, the speedo/odo works fine--I can hit a bump and it (usually) doesn't affect operation.

2. When the speedo stops, the mpg gauge stops working also, and drops to zero.

3. The tach and temp gauge are unaffected.

4. The gas gauge may be slightly affected--hard to tell though.
It doesn't go to zero or full, just reads either a little low or a little high.

5. I recently (Dec) replaced the odometer gears; prior to the replacement, and for three months afterward the speedometer worked just fine.

Suggestions? Any known problem area here (bad circuit board, connector plug that works loose etc?

TIA
mike

[Gregs///M]

Leaking or dead SI board batteries usually have these symptoms. I had this same problem in my car until I replaced the batteries. Its also possible a bad solder joint can cause this but more likely dead batteries because they are over 20 years old.

You're options are to buy a new SI board, used SI board, or you can PM me and I can quote you on replacing your batteries. I have them in stock and also have a replacement board for sale in the classified section if your board is heavily damaged.

[jrobie79]

check the sensor in the diff...the plug from the harness was all corroded on mine, same symptoms... wired up a better connection, and boom

[Dirtboy]

I'm in the same boat as the OP. Same symptoms. My diff sensor is brand new and so is the wiring. It's funny how the speedo only works when it's warm; grumpy old car I guess...

I'll be taking the cluster out this weekend and reflow all the solder joints..

[nando]

my vote is the wiring to the diff sensor. even if the wires aren't broken, the pins get full of crud and don't make good contact.

a dead SI battery usually affects the tach, not the speedo. the MPG gauge needs speed input to work as well.

[Gregs///M]

my vote is the wiring to the diff sensor. even if the wires aren't broken, the pins get full of crud and don't make good contact.

a dead SI battery usually affects the tach, not the speedo. the MPG gauge needs speed input to work as well.

My speedo gauge in my late model cluster was doing the same thing. Usually on the freeway, it would suddenly drop out (not working) for a few minutes. Usually came back on after hitting bumps on the road. The OBC would also not work.

I replaced my SI board batteries and it has since not done it. I have not re-soldered my contacts..

I suppose the cheapest thing since you have a new sender, would be to pull the cluster out and inspect and re-solder. Then replace SI board batteries.