Question about 1999 Land Rover Discovery
Sounds like a faulty Diff Lock switch to me.
Most of the D2 models till late 03 model year use a version of firmware on the SLABS ECU that when diff-lock is detected puts the ABS and Traction Control systems into a lower response mode. Late model vehicles came with factory fit diff-lock linkages as a option, and the firmware was revised to allow this to operate in conjunction with the traction control.
Therefore ABS and TC illuminating (but with no HDC) means your TC/ABS is in the lower performing mode, and your diff-lock may be in, but more likely the £12 switch has broken, and needs replacing. It's a bugger of a job, and can be done from underneath the vehicle (did mine this way) the switch is p/no PRC2911, and just unscrews. It's located just behind the diff-lock stud above where the front prop fits.
Your options are thus:
1) Remove the front prop. Work blind and try and change it by feel alone. Helps if you can clean the area off before too, don't want any rubbish falling in the box! Unplug & Undo the switch, IIRC it's a 12mm head, and a stubby spanner is the tool for the job. Remove, swap the lower nut from the old switch to the new one (important for the length) and put back in. Don't do up too tight, or it may shear off (as my friend did 2 days after I did mine! He kept tightening it...) Pop the connections on and the front prop and the fault should go away. You could also just disconnect the switch if you want. IIRC open circuit is no-diff lock anyway, but if that's not correct then make up a link with some spade connectors and link it out then.
2) Remove the centre console, drill the rivets and attack from above. Same tools needed, just you can see what you're doing.
I favoured Option 1. YMMV!
Your whirring noise and loss of power may indicate the diff-lock is engaging occasionally and may indicate damage to the transfer box.
Posted on Feb 25, 2010
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Posted on Jan 02, 2017
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