Speedometer/odometer issue

Bob Mazzi · Post by **Bob Mazzi** » 30 Sep 2021, 10:24

I am working on a 96 850 wagon. I have a strange, intermittent problem. Over the last few years I've occasionally had the odometer and speedometer not work. But, if I stop and power off the car and restart it, 99% of the time they come back. So, I'm thinking it's electrical. Perhaps a relay that's not latching when the car starts? Over the last few days, it's happened more often, and has worked for a while and then stopped while in motion. But, a shutdown and restart cures it. I'm starting to wonder if Microsoft was involved in the design. <G>

When this happens, the computer also does not register the miles and the displayed MPG goes down as if the car is not moving. But the other gauges seem to work fine. No ABS light, trans light or check engine light. Trans shifts normally, so I'm assuming the speed sensor is still working.

Has anyone else run into this? Am I right in thinking it's likely a relay? And if so, which one?

Teddy1975 · Post by **Teddy1975** » 30 Sep 2021, 12:17

Hey Bob.

The speedo/odometer gets the signal from the ABS module. Do you know if your ABS module has been resoldered? It can cause all kinds of problems when it starts to go bad.

Bob Mazzi · Post by **Bob Mazzi** » 30 Sep 2021, 12:58

I have no idea. Car has 300 plus k on it now, but I don't know what happened before 230k. ABS light is currently off so I assume that it's currently working. Only light on is the traction control and I've never looked into that one.

Post by **misha** » 01 Oct 2021, 03:17

Tracs & abs share the same module.
Time to rebuild abs/tracs unit.

Usually...abs/tracs lights turns ON at the same time when fault code is stored in abs/tracs unit.
Never seen them turn ON separately on cars equipped with abs/tracs unit...unless tracs is disabled manually on the switch.

Bob Mazzi · Post by **Bob Mazzi** » 01 Oct 2021, 18:16

Well, I could have a bad switch. I've tried the switch, but not tested it.