Dodgy Speedo?

[Bowlerwell]

I drove into work on Friday and all was well, but when I drove home the needle on the speedo was reading 0!
The odometer had also stopped turning.
To check it wasn't just a dodgy connection on the back of the instrument cluster, I put on the Diff Lock, and it didn't disengage (I'm assuming the VSS to the diff lock is not routed through the instrument cluster...?).
I presumed it was a sensor(reed switch?) failure, but when I restarted 10 mins later, it worked fine, and has been working all weekend.

Is it possible this switch is on the way out?
Is it a big job to replace?
How likely is it that the failure is correlated with the MASSIVELY warm temperatures in Edinburgh last friday?

[S2central.net]

VSS comes from speedo module in dashboard... You only get a good signal there if the speedo is working and the speedo sender in gearbox is good.

I would have to dig out some old findings I did on the speedo sender - you should check it first rather than condemning the speedo. It should be possible to see pulses on that with an LED type tester - but I cannot remember the voltage range.

I have never tried to replace the circuit on the back of the speedo module - looks darn fiddly but I do know the part number for the speedo chip that drives the clocks and VSS. Anyway - check the gearbox sender first - maybe you just have a bad contact or friction damage thru the loom or something.

[johne]

Mine's been doing the same occasionally for the last 6 months - find a big pothole and it'll start working again

The VSS for diff lock and everything else is routed via the instrument cluster as it's the speedo chip that turns the gearbox sensor signal into the VSS signal whilst buffering it at the same time to drive all the other electronics VSS can go to.

I assume we've both got a dodgy connection between the gearbox sensor and the back of the speedo but I haven't been able to track mine down.

Can't see that it has anything to do with it being warm your way last week.

John

[Bowlerwell]

Great. Thanks Chaps.
Is the sensor on the gearbox easy to get to? Is it replacable by a novice such as me?

[prj]

Why do you insist on replacing the sensor, when it's likely it's just the connection that is bad?
If the connection is bad somewhere, and you replace the sensor nothing will change.

Except for the weight of your wallet that is.

[Bowlerwell]

You misunderstand my tone. I am not insistant.
Believe me, I would definitely prefer to fix an electrical connection than to replace a sensor. You jump to the wrong conclusion.

Nevertheless, I don't know where the sensor lives, and for that matter, hence, where the wiring goes...
I simply ask where it is, and if it is a easy job to replace or not.

[prj]

Okay, sorry...
I am sure someone will post a picture from ETKA shortly

[Bowlerwell]

No problem.
I hope so...

[simon20vq]

I have the same problem, speedo will work but then seems to stick or react slowely, on saturday I jet washed the whole engine area and down by the front drive shafts. Since then things have been alittle better is the sensor on the top or side of the gearbox (I've not looked yet)? Could road crap and grease cause a poor circuit? Anyone got a pic's of that area?
Thanks

[spink]

its childs play to change one of these,not even a screw or bolt to undo.Its kind of held in by itself,will post a pic later if no one else does.If you look slightly above the n/side inner cv joint you will see it

[Bowlerwell]

Nice one. A pic would be useful for if I ever have to change it...

[spink]

here

[Bowlerwell]

Great. Thanks!

[mcandmar]

Its just above the passenger side inner CV joint, as above it just clips into place. You can reach down to it from inside the engine bay.

First thing to do is test the sender, jack the passenger side front wheel of the ground, connect a multimeter to the sensor and measure continuity. Then just turn the wheel and listen for the beeps. If the sensors good then test at the plug going into the back of the instrument cluster.

[S2central.net]

I once had a bad connection from my cluster where the ecu was throwing up codes for
Bad/missing VSS. Worth checking things are nice and tightly plugged in before swapping sensors which can be utterly futile.