My speedometer was functioning intermittently and most recently ceased to function at all. I replaced the differential cover-mounted speed impulse sensor and check the wiring from the sensor to the speedometer. Wiring was fine however, the speedometer was still not working. I checked the harness connection on the back of the speedometer and it too was fine. It appears to be the speedometer itself. Can anyone provide some detailed guidance on how to replace the speedometer on the instrument cluster? Any detailed guidance will be greatly appreciated.

Many thanks.

Only Volvo

Hi _?_,

>(1) I had the differential speed sensor replaced with a new one. (Polarity >wiring is correct.)

Did the connector fail before? Was it rewired?

>(2) Wiring from the speed sensor to the speedometer was checked for continuity >and was deemed o.k.

You can verify the connector with an ohmmeter by checking continuity with your
ohmmeter between 4-pin connector D, Pins 1 & 2. Brown/White & Green/White wires. With the VSS connector unplugged it should be open.
(above to check for possible short circuit at 2 pole female bullet connector)

>(3) I removed the entire instrument cluster and replaced the malfunctioning >speedometer with one that I know worked previously.

Now you must examine the female harness connectors for being damaged/ spread open. I had this problem with a fuel gauge connector.

8-pin connector A Pin #2 Check pin & Check for continuity to ground.
You can check to the ashtray ground. If it is open, then repair ground 31/6
just forward of drivers door down at floor level.

and 4-pin connector D
D1 Green White S+ to speedo
D2 Brown White S- via unspecified item- looks like a capacitor
D4 Brown Red +12V to instrument cluster onboard fuse 11/41
This fuse common for fuel speedo tach & temp gauges.

Give an e-mail and I'll send you the schematics for the speedo.

Bill

B.B.:

Thanks for the very prompt response... and thanks for sharing your detailed knowledge regarding this issue!

I drove the 940 this afternoon and the speedometer and odometer are now working. I suspect that the speedometer that I swapped in place of the bad one had not been in service for at least 2-3 years and may have needed a bit of 'rejuvenation' before functioning. I had only driven the car a very short distance (30 yards) when I concluded that it was not working immediately after installing the replacement speedo... I may have been too quick to declare defeat. I knew that I had installed all wiring and connectors properly as I had double-checked everything.

Fingers crossed that all will continue to function properly :)...

Thank you again for your response!

OnlyVolvo

Hi _?_,

Glad you got it working. Time to fix the old one!

Now use the info from my last post to check the printed circuit paths from connectors A2, D2, D1, and D4 to the speedo connections S-, S+, and + .
You are likely to find a flaky solder connection on the flex card.
If you follow a trace and it stops with a dotted line " ------ "
This means that the track continues on the other side of the flex card.
You cannot hope to reflow the back side solder connections from the top
of the flex card. Then you simply tack a jumper on the top to make the connection
reliable. Take a look at the traces and see if any tracks are like this.
If that doesn't fix the problem maybe the series capacitor hung on S- is no good.

Good luck, Bill

Thanks to all for responding to my request for help regarding my malfunctioning speedometer. That said however, the challenge still stands. I have since done the following but unfortunately, the problem still persists:

(1) I had the differential speed sensor replaced with a new one. (Polarity wiring is correct.)
(2) Wiring from the speed sensor to the speedometer was checked for continuity and was deemed o.k.
(3) I removed the entire instrument cluster and replaced the malfunctioning speedometer with one that I know worked previously.
(4) I checked the OBD for possible fault codes but only received 1-1-1 code indicating that no faults were recorded.

The speedometer and odometer are still not working. I am rapidly running out of ideas. Is there a primary fuse that protects the differential speed sensor circuitry? If so, can anyone advise me regarding its number and location?

Any further advice will be greatly appreciated!

Many thanks!

OnlyVolvo

Hi _?_,

Before you dig into the speedo, check OBD port A-2
see if you get a 3-1-1 code (missing VSS signal)

The VSS vehicle speed sensor is polarity sensitive.
There's a 50-50 chance that it's in backwards.
I found this out recently the hard way.

It's easy to correct by removing the VSS connector, and opening the connector shell and switching the two bullet connector wires.

Cheers, Bill

https://www.brickboard.com/FAQ/700-900/ElectricalSpeedometerRepair.htm
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now