Hello all...I've just resolved this most written about fault on my 1999MY Defender TD5, but thought i would share my issue with all owners of similar year / model.
I had 2 lights ABS & TC both wouldn't go out stationary or above 5mph, my primitive code reader tells me "shuttle valve fault." Read plenty of other owners resolutions but decided to go the route of removing the ABS modulator entirely from the Landy. Took about an hour to get the unit out without undoing pedal box or anything else...I started by removing b/fluid from the reservoir (syringe) then undoing the 10mm nut at the front and lifted the unit up and pulled it forward out of the 2 rubber mountings at the back (don't bother trying to get a spanner down the back), with the unit free of the mounting plate i undid all the brake lines covering each line with small plastic bags to catch any residual brake fluid. Now the unit is free, it's tricky but i turned the unit upside down, pulled off the rubber hood seal near the windshield and with a lot of "Jiggling" it will come out the hole. The 3 allen screws holding the shuttle switch are locktited in so... i backed off a bit then did the screw up, then repeat several times to clear the thread lock so i didn't end up with a sheared bolt or head (as some have done). The replacement switch cost me £38.00 but i decided to do the MOD that the Disco owners have been doing, with bringing the wires out through the bottom in case the ABS internals were dry solder joints. Replaced the switch and then refitted the ABS module back in Landy (same direction i got it out). I completed the MOD wiring into the harness connected all the brake lines and pre-purged the ABS module by getting "her in doors" to press the brake pedal down and backing off each brake line until Brake fluid was seen. The brake pedal was ok (a bit spongy) so needed to have all 4 wheels bled before 100%, however i thought i would see of i could clear the 2 amigos.....NO...fault still there!!!!!!! Did some more research on here & elsewhere and used a tip from another owner who gave a good write up on readings using DMM. When i checked pin 9 & the earth pin below it on the modulator i was getting 0 ohms (it should be above 3K), so i decided to remove the Disco MOD and recheck...now i was getting 3.5K...plugged it all back in tried cycling the ignition and TC light went out. I then reversed out the drive (brakes did work!), the ABS light also went out so....all fixed !!!!!
Unless somebody wants to chip in here the Disco MOD didn't work for me? in fact it grounded the shuttle valve and caused the fault to persist. Hope this helps another Defender owner coz all you owners out there sure help me a lot with keeping my old girl on the road. TS

Well done on repairing it, much cheaper than a new ABS modulator.

l had a similar shuttle valve fault code, my local LR specialist said one issue is that the ABS rarely kicks in on a Defender driven on road.
He reset the fault and did a few emergency stops on a nearby gravel track. After that the ABS worked fine but he told me to try and use the ABS every so often, maybe by getting two wheels on to a verge and hitting the brakes.
He said it stops the shuttle valve from sticking.