Odometer roll-over 'fix'

[PhilipC]

For anyone who's suffered the odometer not rolling over on the 1000's (sounds like this might be everyone to some extent) the solution is as follows:

1) Remove dash top
2) There are three pairs of wires going into the back of the speedo unit - these are for the three bulbs (illumination, 2 x warning lights)
3) There are three separate wires that attach directly into the back of the unit (screw terminals)
4) The black wire is ground, the green is live, and the other (orange-ish?) is a pulse-feed
5) Disconnect the pulse-feed wire
6) Connect one end of a loose wire to the live feed, and repeatedly touch it to the terminal where the pulse-wire was connected
7) The speedo should show a small reading (I got about 5mph with rapid connectdisconnect) and the odometer will very slowly advance
8) Restore everything as it was

I did this with the engine running to ensure I got a good voltage, and ensured that I made contact to the pulse feed for the smallest possible time in case it didn't like it. Usual disclaimers apply: this might blow up your speedo, your car or your house. You never know...

PS: You'll probably need to undo the speedo retainers and pull it forward to get any access to the terminals at the back.

PPS: Yes, leaving it overnight and hoping is simpler, and driving over cobbles might fix it, but like this you can ensure you don't lose too many miles on the clock.

[simpo two]

PhilipC said:

like this you can ensure you don't lose too many miles on the clock.

Why would you want to keep them? Up to a point I would call it providence!

[julianhj]

The couple of times it's happened to mine it has cured itself within 20 - 30 miles of 'spirited' driving. Cheers for the tip though!

[shpub]

I wouldn't recommend this as the input to the speedo feeds a logic chip and this can be very susceptible to sparking caused by the technique you describe. Especially as the source is from a sensor which usually has some form of current limitation in it to prevent spikes and surges. Very easy to screw up the electronics inside the speedo unit itself.

[pbrettle]

Also spoken to a local dealer to me who is quoting £65 ish to get it fixed.... if you can fix them permanently then fine, but probably better in the longer term to get it fixed....

Mines currently 50% under what is should be saying... but it makes sussing out when the servicing is due a nightmare! Oh, and with that dodgy fuel gauge, playing with fire...

[PhilipC]

Stuck for a few thousand before last service, and dealer charged what seemed like arm + lower leg to remove, send to TVR and re-fit. Stopped again at next 1000, so took it back. Fixed on-site without charge by manually pulsing speedo (so I hope they are more cunning than I if these are the risks), and was fine for 42K and 43K (well, certainly under 50 miles). Decided not to take any chances at 44K. Agree that the main grief is needing to keep track for service reasons. Odd mile here or there doesn't matter too much, but if it's a % of service interval I'd rather get rid of the problem.

As soon as I can sort out a high-speed solid-state switch (I'm thinking high-speed transistor, since the current is low, or possibly a FET) I'll see about a proper solution. This was just a prototype ;-)

Has anyone else tried this kind of thing?

[phlap]

Mine stuck as it rolled over to 30K. Tried the 'spirited run' approach then some gentle persuasion without success.

Wasnt expensive to fix, it just took a couple of weeks to turnround the gauge. Main problem was using the tinbox to go to work every day. I suspect the BIB would take a dim view if having pulled you over they noticed a large hole in the dash where a speedo should be

[chimhunter]

Mine just did the 30k thing as well. Unfortunately it did it right before a track day. You would have thought that some 'spirited' driving on the track would have fixed it. Alas no, but a night left outside and a quick run the next day seems to have done the job. None of that dashboard malarky for me then.

Rob