Vehicle & Technical > Discovery

300tdi speedo????

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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.

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