In my 1992 Volvo 240 wagon, we removed the rear ABS sensor on the final drive, which seems to share with the speedometer and odometer, to clean it. After that the speedometer doesn't work. After hitting a bump it seems it will fluctuate up to about 20 then drop. Just hoping that the sensor isn't in quite all the way or out of alignment perhaps. But what do you think I could do to try and fix it?
Any suggestions are greatly appreciated.
Thanks

 

you probably broke the wire, maybe inside the insulation near the sensor... surprised you're not getting ABS faults too.

 

Haha i was having ABS faults... that was the reason for removing the sensor... How should i go about seeing if wire is broken?

 

unplug it at the back of the speedometer, and use an ohmeter on the signal and ground wire, which are pins 1 and 2 of the 4 pin connector 'D' on the back of the instrument panel. spec says 1820 ohms +/- 180 ohm (so anything from 1640 to 2000 ohms is OK). the wires are brown-white and green-white, where the brown-white wire is normally grounded inside the instrument panel. from the instrument panel, the twisted pair of bn-w and gn-w goes through the large A pillar connector, down the drivers door sill, and through a 2 pin connector in the trunk area and on to the speedo/abs pickup. on the sensor end, the brown-white wire turns brown.

 

Figured it out... after reviewing the Bentley manual i noticed it said something about how tight the screw holding the sensor into place must be. After tightening it, worked like a champ.

 

It's been sometime, and lately if I hit bumps, my speedometer wobbles erratically. Today I tried tightening that same screw, and tightening it some more. Still wobbles when I hit bumps. Any suggestions?
Thanks!

 

might be an electrical connection at the speedo end?

 

Perhaps. The thing that connects it, if memory serves me correctly, is that ribbon type cable with the protective clip over it?

 

hmm. I think thats it, but I've not taken a 240 instrument panel apart, only my 1992 740's.

the late 240 wiring diagrams show 2 connectors in the middle, but not where they are located. it shows it goes a 3 wire right angle edge connector that goes into the back of the speedo cluster. the blue wire is switched power from the ignition key, the green-white wire and the black wire go to the sensor in the differential, with the black wire being grounded (probably at the front-left side of the gear shifter). it shows the wire is routed along the driver side door sills from behind the back seat, to near the fuse panel.

 

I checked the wire at the speedometer today. It was a little loose. I also noticed that the protective clip wasn't on it. (Add another thing to the list of things that a mechanic in Lincoln NE didn't do correctly when the blower motor and A/C was fixed.) It still wobbles a little on bumps. But no where near as bad it seems.

 

several HOWTO's I've read suggests cleaning all the electrical connectors on the instrument panel with deoxit cleaner, then putting a tiny dab (toothpick?) of deoxit gold on each connection. many are sensitive enough that any disruption in the Force brings out the Dark Side.

 

Thanks. I should be able to pick some up today.

 

Fixed the issue with the speedometer. Upon closer inspection of the wiring harness to the sensor of the differential, I noticed bare wiring. After separating the two, and wrapping some electrical tape around the two wires, my speedometer is normal once again.