When I start up my 99 Disco II, the transmission oil cooler sensor light comes on and stays on. This happens immediately when I start up the vehicle, without having driven it or even warmed the engine up. So I suspect that it's the sensor that's the problem. Where is this sensor and how easy is it to replace it? I can see a sensor on the side of the transfer box. Is this it?

 

Yes you can replace the sensor, order a new one and then repalce the old one.
www.atlanticbritish.com
Also check with your local dealer, it might be cheaper once you include shipping from AB.
Unplug the sensor, clean the connections and the plug it back in and see if that fixes the problem before you order a new one.

 

Spikes advice is good and def worth a try,

but the sensors are known to be "iffY".

NAS D2's have 2 sensors, one in the transfer box and 1 in the Auto gearbox cooler both linked to the SAME dash warning light.

Autobox cooler one here, accesible from panel under front right wheel arch....common one to fail, I have replaced mine, although I did it by removing half the front end and taking the cooler right out, but Im pretty sure you can do it through this panel.





transfer box one here

 

Wow Nick, your radiator is all corroded mate, whats up with that?
Looks like youll be needing a new one soon.

 

The very front one is the aircon rad (which I assume your talking about), it "Looks" corroded, its actually dried mud / crap what ever after she swims muddy puddles

 

Ok, my mistake, I see it better now, yes it is the A/C condensor thyat I was refering to.