So, one of the perennial items on my "to-do" list has been to check out the ABS system. Not sure if this is common across other generations, but the 964 is known to have issues where because the ABS is never tested or used in anger, the actuators seize. First time you get to find out about this, is when you need to really stand on the brakes. Skid skid bang.
A number of years ago, a Rennlister called Michael aka "cajonfan" sat down and designed an ABS test unit for the 964 C2 (same system as used on the 964 Turbo). It uses an old ABS control unit housing into which he's build the test rig. It's brilliant, but it's been sat on my toolbox for 7 years now. I did exchange some PM's with him at the time, lovely guy and I know he was also working on a similar test rig for C4's, clearly a far more complex system with it's diffs and 4wd....but I've not kept abreast of what's available now, so if you are in the market for either, then maybe reach out to him over on that forum.
Cajonfans 964 C2 ABS Tester
Cajonfans 964 C4 ABS Tester thread
Along with the test unit is a document with a full suite of tests to perform. The tests include things like checking the resistance of each ABS wheel sensor, simulation/activation of ABS scenarios, various voltage measurements to be taken under these conditions, and so on. Clearly you need to jack up each corner multiple times in order to check whether the valves are actuating and either locking the wheel or pumping and still allowing rotation. The one thing it doesn't do, is run a diagnostic against the ABS control unit itself.
(Photo's courtesy of cajonfan)
Once I was underway, all 7 major tests (with their sub-tests) were done inside an hour. Thankfully my system passed each test with measurements that were spot-on in the middle of the anticipated ranges. I did note than on one particular corner, the valve seems to be reluctant and "sticky" to start with but after being exercised for a minute or so, it sounded like the other corners. If you did come across erroneous readings or malfunctioning sensors, there's also a full fault-tracing and diagnostic section in the documentation. I think I'll be adding this test routine to the annual servicing activities, knowing that the ABS can silently go AWOL.