Oh, you have TCS too!
Yep, that's not in the main manual and no-one's been able to find a supplement that covers it either
I'd interpret it to be the same code.
Looking at the manual, some of the fault finding for that code does get pretty involved.
If it only fails when chucking it around, it could still be a wiring fault or one of the grounds it mentions though? (The vibration/motion could cause the intermittent break to occur).
Does the 4WS light always go out every time from start up?
If it sometimes fails on start up, then I'd definitely suggest it's worth trying the re-solder trick on the ECU as a possible quick win, before looking to chase out all the wiring or investing in an analogue meter. I say that because on the fault tree for code 20 each of the branches does end in fault ECU if everything else checks out, so it would still fit with that. If it is the ECU though, I would expect it to sometimes fail on start up
Even if it doesn't always fail on start up, it probably is still worth trying re-soldering, because it's pretty straight forward to do and it is a common problem on them now they've aged. Trying this could still avoid the more involved fault finding.
The guide to re-soldering is here btw:
Written guide;
http://honda-tech.com/showthread.php?t=886363
Pictures;
http://honda-tech.com/showthread.php?t=886363&page=3
Personally I re-soldered a few more joints than just the ones they've highlighted.
Keep us updated how you get on and we'll be happy to help further where we can!