unstable reading of speedometer

romette · Post by **romette** » 21 Nov 2011, 08:39

The speedometer of my volvo 960 summum, 3l,24v, 1991 is occasionally unstable. While running at 120 KM/h, the reading may vary from 0 to 160 very erratically.
Do you have some clue about the origin of this problem: wiring, sensor, electronic?
Thanks for your help

Billc1015 · Post by **Billc1015** » 21 Nov 2011, 09:36

Your symptom sounds like a speedometer cable that is binding. I do not know if a 91 960 uses a cable or if it is an electronic speed sensor. If it does use a cable, I would start there.

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Post by **billofdurham** » 21 Nov 2011, 11:25

Welcome to Matthew's Volvo Site.

The 960 does not have a speedo cable. It works from a sensor in the differential housing about 3" above the filler plug. Check the connection at the speedo sensor. Be sure it's secure and check the connector and sensor for signs of corrosion or oxidation. If there is, spray with electronic deoxidizer and clean it. As much as possible, examine the harness for any signs of a break or tear, or for signs the wire might have been cut. If it's not wiring, then it's either the sensor or the electronic speedometer head. Also check the connector on the back of the speedo head for possible intermittent contact.

Bill.

romette · Post by **romette** » 25 Nov 2011, 09:02

Hi Bill, from Durham
Effectively my speedometer as an electronic connection to a sensor located on the differencial cover. However I obtained an exploded view of the differencial and it seems that the sensor is on the back cover of the differencial (back side of the car on the opposite side of the filling plug). Is that the right one? How to access to the device, the place is full of supports of all kind?
Thanks for your help
JL

Post by **billofdurham** » 25 Nov 2011, 11:26

My apologies. On the 960 the filler plug is on the front of the differential case. The speedo sensor is on the rear plate. Access is easy as it is only held in by one hex socket screw. Remove the screw and the sensor pulls out.

Bill.