Speed sensors

[Yomper]

My speedo doesn't work for the first 20.odd miles then the doors auto lock and speedo starts working.
Pretty sure its the speed sensors 
Its a 2011 1.6 hdi the. old shape.
Do I need new sensors or would a clean do it?
Also where are they haf a.look quickly but guess I need to jack up? The bottom engine cover has been removed already. 
If I need new ones I looked on ebay  but get bogged down as there are so many any cheap shops that will do a good price..tia

[brodfather11]

There are 4 speed sensors , connected to the ABS , one on each wheel if you have ABS fitted.
 
 The speedo drive sensor is on the back of the gearbox n/s above the drive shaft . Boilocks  

Seemily the speed data is from the engine ecm and the abs wheel sensors according to haynes manual 


 I would disable the autolocking and do a BSI reset , (instructions on the forum) then see what happens

[Yomper]

Thanks I will look for the bsi reset

[Sol]

The front sensors are inserted into the hub carrier and measure the magnetic wheel bearing in the hub. The rear magnetic bearings are built into the factory oem brake discs but the sensor is again embedded in a hole in the hub.