300tdi speedo????

[mr_disco]

hi all my speedo aint working any ideas

so far i checks all fuses
took the clock out to check for loose conections
changed the little black box thing on the gearbox

im all out off ideas and dun fancy splashing out on a new clock just yet.. any trick out there please???

lol  :dance:

[mud knight]

it will be a loose conection on your alternater :doh:

[boss]

haha did you do what i did and forget to check the fuses under the dash?

[Range Rover Blues]

Try a secong hand dash binnacle then.  The sensor is pretty robust, on the RRC it serves the cruise, EAS, EFi and speedo.  You can check the input with a multimeter, with the ignition on the input should fluctuate between 12volts and 0 volts if you turn one back wheel.

[jnoshea]

Does the speedo sender unit on the transfer box dish out a voltage then? I've taken mine off to clean it, but when I measure across the terminals while turning the square drive, I don't read anything (although the resitance does change). I guess this is because it needs a power-supply from the car before it can function, or is it broken? When you test it on the car by turning the back wheel, are you measuring on the terminals of the sender unit itself or at the instrument binnacle? If at the sender, then this is no different to me turning it by hand (or drill) in my kitchen.

At the moment my speedo is bouncing between zero and around half the speed that I'm actually doing. The square drive on the sender unit is not excessively worn.

[jnoshea]

Actually, perhaps the sender unit just returns open or closed depending on the position of the shaft, so as it rotates you get pulses of voltage going to the electronic speedo, which then translates this into a speed based on the frequency of the pulses. This would explain why the resistance goes from 120 ohms to open circuit when I test the sender while rotating the shaft. Does anyone know if this is the right way to be thinking about this?  :?

[jnoshea]

Ok, I've worked it out now with the help of the workshop manual.
The speed sensor does indeed work by sending voltage pulses to the speedo. It does this by pulsing between 0 and battery voltage, apparantly 6 times per wheel revolution. The series of pulses is interpreted by the Vehicle speed sensor inside the speedometer instrument and translates into the needle position. I guess if my speed sensor at the transfer box is working i.e. open and closed circuits as it rotates, then the problem must lie at the speedo end. I'll let you know if it works.

[craig_midz]

quick way to heck ya speedo is undo ya speed transducer an spin it with ya fingers while someone watchs speedo with ignition on if speedo works then it will be the speedo gear in the transfer box which was what was wrong with mine the square hole had rounded an they are a piece of [throw it] 2 change an cheap 2

[jnoshea]

That is genius. Thanks.