Speedo not working - not the usual (I think)

[jammy_basturd]

The speedo was never great under 20mph, but after an extended period for the car sat on the sidelines, during which the diff was replaced, the speedo doesn't work at all!

To begin with I tried closing up the clearance on the existing sender without any luck. I've now just fitted another sender, screwing it in so that it touched the toothed wheel and then backing it off not even 1/2 a turn. Span the wheels round to make sure there was no contact (which there wasn't), but still no joy on the speedo.

So, on to continuity checking.
From the black wire in the grey connector (by the diff) to the earth point in the boot - fine.
From the slate wire in the grey connector (by the diff) to the slate wire connector for the door/window ECU - fine.
From the slate wire in the black connector (J33) under the helmet holder to the black connector under the dash - fine.
From the slate wire in the black connector under the dash to the connector (yellow) on the gauge - fine.

I realise there is a gap in my checking from the boot to the connector under the helmet holder. I plan to check this tomorrow.

So, it seems there could be three things wrong:
1) Broken gauge
2) Two duff senders
3) The missing link of continuity checking.

Can I put 12v onto the yellow connector on the guage where it is in situ to test the gauge?

Any other possibilities I've missed?

[ukkid35]

I was in the same position as you, thinking can I possibly have two duff sensors? So I bought a USB oscilloscope and connected it to the sensor to check with the engine running in gear on jack stands. Nothing.

Fitted a new sensor, checked again and got this



Connected it up and all good.

Let me know if you need a new sensor, I haven't renewed my ad in the classifieds, but will do eventually.



You're welcome to borrow the USB oscilloscope, but I'm away for a couple of weeks, I only paid £20 for it on eBay.

[jammy_basturd]

A USB oscilloscope?! I never even realised they existed! I've had a couple of occasions when I've thought it would be useful to have an oscilloscope so may invest in one myself.

Not sure which to go for:
http://www.amazon.co.uk/Hantek-Digital-Storage-Osc...

http://www.amazon.co.uk/1008C-Oscilloscope-Program...
I'll order it from Amazon as I have a Prime account, so I can get it tomorrow.

[ukkid35]

jammy_basturd said:

I'll order it from Amazon as I have a Prime account, so I can get it tomorrow.

If you weren't in a rush you could have gone for this for £16

http://www.ebay.co.uk/itm/121401801984

[jammy_basturd]

I'm rather keen to get it sorted so I can get the car MOT'd - it's been a long time coming!

Do you know your oscillators? I'm thinking about getting the second option as it has more features, but want to make sure it'll be suitable for this job first!

[GT6k]

That Hantek scope looks good, I use various Picoscope models at work which are more expensive (£150 vs £50) but still a fraction of the cost of the old time storage scopes.

http://www.maplin.co.uk/p/picoscope-2205a-dual-cha...
http://www.amazon.co.uk/PicoScope-Channel-Oscillos...

[Supateg]

I have the

Dso nano v2

http://www.seeedstudio.com/depot/DSO-Nano-v2-p-681...

Version 3 out now.

[jammy_basturd]

Thanks guys, I've gone for the more expensive Hantek device. I doubt I'll get so much use out of such equipment to warrant spending £100+.

Does anyone know if I can stick 12V through the speedo gauge to test if it still works?

[Tarmacshredder]

You don't need a speedo for the mot so it won't stop you getting it mot'd, use a sat navigation for the speed until you can get it fixed. Sorry doesn't help work out what's wrong but at least you can use it and enjoy it before the summer is over.

[jammy_basturd]

Tarmacshredder said:

You don't need a speedo for the mot so it won't stop you getting it mot'd, use a sat navigation for the speed until you can get it fixed. Sorry doesn't help work out what's wrong but at least you can use it and enjoy it before the summer is over.

By golly you're right! I had Googled and found this page from The AA: http://www.theaa.com/motoring_advice/car-servicing... which suggests the MOT was changed to make sure the speedo works.

However checking the MOT manual itself, it makes no mention of the speedo working, just that the glass can't be cracked and it must be able to be illuminated: http://www.motinfo.gov.uk/htdocs/m4s06000801.htm

[Tarmacshredder]

There are lots of things you would not believe for the mot! Lol the mot station has no way of testing the speedo unless they were to take it down the road which isn't part of the mot. I have been taking 1 vehicle for over 4 years with the same mileage as the cable has snapped for the speedo head, the vehicle does very few miles but they never question it.
Other oddities of the mot include if you took a vehicle with a missing wheel nut or bolt it would fail. If you took the vehicle back with a hub cap fitted it would pass as they would not be able to inspect if the wheel nut was present and they are not allowed to remove any item to test at the mot! If you had a cracking in the windscreen in section A it would fail but if you took the vehicle without the windscreen and wipers fitted it would pass as the windscreen would not be able to be tested as not fitted! And believe me the are plenty more.

[jammy_basturd]

Got the Oscillator through, took a while to get installed properly due to Hantek not knowing how to package drivers for Windows.

For anyone else wanting to know how to installed the Hantek 1008C I had to download the drivers from here, then follow these instructions: http://www.hantek.org/asken/iaskdetail.aspx?id=201....

Anyway, clipped the oscillator on to the back of the connections on the speedo and it was pretty cool to see the waveform on the laptop! However the speedo was also working now!

Definitely a dodgy connection behind the dash as it sometimes takes a minute for the speedo to start working and now the rev counter doesn't work!

I'll shove it through the MOT and then rewire the dash.

[N7GTX]

jammy_basturd said:

and now the rev counter doesn't work!

Big fuse???

[jammy_basturd]

It was working prior to me taking the dash off, so I suspect I've disturbed a wire by one nanometre which is enough to stop it working!