I have a problem with the speedo in my '92 UK spec 300ZX auto, it suddenly dropped to zero shortly into my journey, flicked back up to show the correct speed a couple of times before dropping down to zero & staying there permanent. Without the speedo the power steering cuts out after a short time & the HICAS lamp comes on.

 

I have replaced the speed sensor on the auto gear box to no avail & tried a new speedo unit to no avial. Last weekend I jacked the rear of the car up & measured the ac voltage out of the sensor whilst in gear, ranged from about 1v rms to 3v rms depending on speed. Checked I was getting the same out of the 2 pins on the connector that goes in the back of the speedo unit. This was with the speedo disconnected.

 

Once plugged in this drops to a few tens of mV at idle to approx 200mV rms at speed. I measured across the rev counter & got a similar range so the speedo meter is loading the sensor OK I would assume?

 

I have been through the wiring diagram & the speed sensor appears to feed straight to the speedo, where one side of the sensor is grounded. The same connector sends speed information to the differential oil temp sensor & ECU, could it be a problem with one of these dragging something down on the speedo circuit?

 

Anyone have a circuit diagram of the speedo?

Call Jeff @ Z-world i think he know's this problem........

can you post your findings when you get an aswer coz mine does this and have to turn car off and on again then it works fine dont do it all the time like your one

cheers

rob

UK model mmmmm

Thanks to alexporsche for pointing me towards Jeff at Zedworld, & thanks to Jeff for the advice!

 

It appears to be due to a bad connection/cable between the speed sensor & speedo unit. Rather than try & find it I took Jeff's advice & ran new wires from the sensor to the speedo. I tried it with keeping the old wires still in place, i.e. in parallel but it still did not work. So I ended up disconnecting the old wires completely both ends & just using the new wires, & appears to work fine.

 

I had the turbos replaced a few months back so something probably got disturbed then...

how did you take out your clocks with out doing any harm ?wheres all the screws please so i can do mine because mine works when it wants to?cheers

There are 2 screws on the under side of the dials cover. remove these & you can take the cover off. Each side pod (a/c controls on left, light cruise cont etc on the right) has 2 screws at the bottom, remove these & they will pull out. 2 more screws on each side hold the sides pod in so remove these & you can remove the main facia panel. I think it was clipped in along the bottom above the sterring column so prize it off gently. At the top of the dials enclosure there are 2 screws, remove these. I also removed the cover from the steering column around the ignition switch. I think that was about it.

 

I ran the new wires throught the bonnet release cable hole in the drivers side footwell.

 

Good luck!

There are 2 screws on the under side of the dials cover. remove these & you can take the cover off. Each side pod (a/c controls on left, light cruise cont etc on the right) has 2 screws at the bottom, remove these & they will pull out. 2 more screws on each side hold the sides pod in so remove these & you can remove the main facia panel. I think it was clipped in along the bottom above the sterring column so prize it off gently. At the top of the dials enclosure there are 2 screws, remove these. I also removed the cover from the steering column around the ignition switch. I think that was about it.

 

I ran the new wires throught the bonnet release cable hole in the drivers side footwell.

 

Good luck!

cheers.