Speedometer
 

Been looking at the faulty speedo, starting with cleaning up and reinsulating the sender unit connector. The speedo occasionally shows signs of life by snapping from zero to speed, but when you come to a halt it generally sits at zero after moving again.

Is an intermittent fault more likely to be the sensor (electro mechanical) than the speedo unit (electronic)?

The sender unit located in the differential is also the rear ABS sensor. If your ABS fault warning light extinguishes once the car is moving then the sender unit is probably OK. Most of the faults as you describe are caused by the instrument cluster PCB, it’s connections or the speedo. condensers or a combination of all those.
There are many useful threads regarding speedometer problems. Try searching in this section.
Questions, Year and model of your car, and
The make of your speedo. Yazaki or VDO.

As ^^ it all depends on car model and oem. For VDO see Dave Barton's website at:
https://www.prancingmoose.com/740-odometer-repair.html

Bob :)

i replaced the sensor hoping it would be that but to no avail...probably dry joint.

What model, year, ABS or no and what make speedo?

I had similar to this the other day and it was neither the speedo nor the sensor but is fixed now.

Just thought id give an update on this for any 91 & 92 940 owners with faulty speedos.

I recently purchased one from Volvo Recycled Relics via ebay. The way this works is focussed on domestic purchases, so in an ideal world you pay for the item, send the complete cluster and they rebuild with a rebuilt speedo set to your mileage and ship back to you fully tested.

I contacted Russell who helped me by dispatching a rebuilt speedo without me sending my cluster first. They are understandably cautious about this as they lose control of the build.

It took about ten days to arrive, there was no import tax to pay and it was securely packaged in another plastic cluster. This proved to be invaluable as there was a slight dimensional variation between my cluster opening and the american speedo, so i ended up using the american cluster and speedo.

As a bonus he sent a foc clock as mine was running slow. So dispite the car currently running like crap, i finally have a working speedo, odometer, tripmeter and clock.

https://www.ebay.co.uk/itm/Volvo-199...-127632-2357-0

Hope this helps another 91-92 owner.