How do you fix a speedo sender on a fiat punto speedo reads 0 all times changed the sender on top of the gearbox power is getting to the sender but speedo registers 0 at all times?

Answer 1

The symptoms suggest that the speedo sender drive shaft has sheared. If you have changed just the sender unit on top of the gearbox, it's possible that you have not noticed that the residual piece of the drive shaft remaining in the support tube -on to which the gland nut normally retaining the sensor engages- freely rotates (which it should not do when the engine is not running) or the broken end of the shaft has fallen away unnoticed when you removed the original, apparently defective sender unit -or possibly left attached to the discarded sender and, again, gone unnoticed. A replacement serviceable sender will still install on to the support sleeve but there will be something like a 12 mm gap in the drive shaft where it should engage in the internal sender drive coupling. A new sender will also engage onto the sheared end of the drive shaft but the sender armature will not rotate and your speedo will remain inoperative. (Check the sender itself by turning the sender internal drive with e.g. a screw driver and watch to see if the speedo "kicks" - the ignition has to be on) You will need to remove a small 10 mm a/f hex headed fastener from the engine block immediately below where the sender is located. The sender drive shaft with its integral drive helical gear/sleeve can then be readily extracted together with the support sleeve with its threaded end (onto to which the actual sender is retained by the above mentioned gland nut). It will be obvious if the drive has sheared if the sender has already been seprated from the helical gear drive shaft/sleeve assembly or will immediately become so when the sender and helical gear/sleeve are dismantled....good luck.