Trip computer inputs from ECU?

[mcandmar]

I remember Paul doing a write up about the speed sensor signal, i recall something odd about the gearbox sensor feeding the cluster which in turn cleans up the signal and feeds it into the ECU. So maybe the ECU isnt getting a valid speed signal which in turn is messing up its consumption output to the computer.

[newsh]

If it's not disengaging automatically either the wire going to the diff is cut, or you have no speed signal.

Did it use to disengage automatically before?

Yes, I'm pretty sure it did. I had the centre console out not long ago to fit the new carpet, I'm wondering if I've trapped the loom to the diff switch, I'll investigate further tonight. The thing that was misleading me was my assumption that the speedo signal and the speed signal on the blue/white wire were the same..

[newsh]

I remember Paul doing a write up about the speed sensor signal, i recall something odd about the gearbox sensor feeding the cluster which in turn cleans up the signal and feeds it into the ECU. So maybe the ECU isnt getting a valid speed signal which in turn is messing up its consumption output to the computer.

I'll have a look for that.

[Nuvo]

I'll have a look for that.

No need. Click here.

[newsh]

Ta Nuvo so I should be seeing a 2.5mSec pulse width VSS signal on the blue/white wire which increases frquency with speed. What I've got when driving along is 12volts and some noise.
The 12v goes away when the ignition is switched off but strangely I was sitting there looking at the scope when the courtesy lights switched off automatically and the 12v reappeared again! Could this be my current drain too! Looks like I've got a short between 12v and the blue/white wire somewhere! But where?

[newsh]

Ah!
I was sitting watching the 12v on the scope and switching the interior lights on and off a couple of times and the voltage suddenly disappeared. Went for a drive and it was all working, speed pulse visible on scope!

Then it stopped, then it was ok again

Interior light signal comes from Central locking pump, does the blue/white wire share the same loom?

[newsh]

No blue/white in the central locking loom.

The fault has not come back.

[newsh]

I hate intermittant faults

[newsh]

So everything is now working as normal, I have no idea what I did to make it ok but I must have disturbed a short between the 12 courtesy light circuit and the blue/white VSS wire. Possibly behind the radio.. If the issue comes back I will at least know where to start. I may well take out the centre console again and check that nothing is trapped. Also my loom has shed most of it's cotton tape covering so is a right rat's nest, it needs sorting out or more things will start to go wrong!

Thanks to all for the advice and input, it really helps!

[Tonks4x4]

Vehicle wiring products sells the original cloth tape....

http://www.vehicle-wiring-products.eu/VWP-onlinestore/sleeving/tape.php

Cloth tape, adhesive. Black
Rayon cloth harnessing tape.
Halogen free, self extinguishing. 19mm x 12metre
Ref: 3380 £2.47 each, £22.27 for 10. Quantity