fless1 wrote:easy to install myself?
If you feel comfortable doing pads yourself (and/or have done that before), swapping/testing the sensors is a walk in the park...
There's one sensor per axle (LH front, RH rear from memory), they're 'embedded' into the brake pad.
Basically, the sensor consists of two wires that act like a switch when the wire insulation wears off with pad wear.
You can test sensor wear or malfunction by disconnecting the sensor: just follow the wire from the caliper and you'll find the plastic connector that hooks it up to the wiring loom. Disconnecting the sensor (again: from memory) suppresses any 'pads worn' signal from the sensor.
This google search retrieves some pics that may be helpful: https://www.google.co.uk/search?q=xj40+ ... ear+sensor