Porsche Enthusiasts Club Forum

Hello everyone and hope you're all well .
I've owned a 968 Cab 94 reg since Nov.17 and only just got round to use it but I've run into a couple of problems , the car starts and drives ok but the odometer/speedo and rev counter don't work .
Odometer
I've checked all the fuses in the fuse board twice , alll ok.
Checked the two cogs inside the speedo and both look ok.
I understand the signal for the speedo comes from the NS front wheel ABS sensor via the Frequency converter relay at G16.
Is it just easier to buy a new relay ( very expensive ) or can the old one be tested ?
The ABS warning light isn't on
Rev counter
Which I think gets a signal from the sensor on top of the Flywheel/Clutch bell housing . My thought is if that sensor was faulty the car wouldn't start and run .
Do the speedo and rev counter both get a signal from the Frequecy converterat at the G16 position .
Hope this makes sense I'm no mechanic but like to try and I'd be grateful for any advice /help .
Thanks Ralph

I may be wrong, but i thought the 968 was the same as the 944 S2 where the speedo is driven by a sensor on the gearbox. This is the part I changed to fix mine last year.

Bear in mind they are £600 new - I got one from a scrapper on ebay for £70.

Speedo & Tach will be different issues. You really need a scope to see if you're getting a pulse from the gearbox at the dash end. Common issues are bad connections at the sensor and possibly bad sensors although that's rare.
The tach is fired from the DMU (I think) but yes the signal comes from the flywheel sensor to the DME. No flywheel sensor it doesn't run. Again I wonder if you have bad connection on the back of the dash.

Hello Ralph,

For the odometer/speedo issue, it's a good idea to check the Frequency Converter relay (G16) as you've mentioned. You can test the relay by swapping it with a known working relay of the same type, typically found in the fuse box. If the speedo starts working, then the relay was likely the issue.

As for the rev counter, if the sensor on top of the flywheel/clutch bell housing is faulty, it can indeed cause issues with the rev counter. While it may not prevent the car from starting, it can impact the accuracy of the rev counter.

In summary, checking and potentially replacing the Frequency Converter relay for the speedo issue and examining the sensor on the flywheel for the rev counter are good steps to take. If problems persist, it may be worthwhile to consult with a Porsche specialist or a qualified mechanic for a more in-depth diagnosis.

Best of luck with the troubleshooting!

Thanks for the help/advice , I did get some electrical contact cleaner and the speedo and rev counter are both working . As for the speedo sender unit I looked all over the gear box and diff and the only electrical connection I could find was for the reverse lights just above the off side drive shaft . While the rear of the car was off the floor I did start the car and go through the gears but no speedo , the car was then put back on 4 wheels and driven on the road and the speedo worked .On the Rennlist site , 968 forum , Speedometer signal output , goes on to say the signal for the speedo takes this route.
L H front wheel ABS senor into
ABS module into
Frequency Converter into
Speedo
It gives much more information than these few sentences but you can get an idea.
Hope this helps someone else and thanks again , Ralph