OK, so today I had a rare combination of time and motivation to get on with this fault, so I removed the ABS module and had another go at soldering the pins on the PCB.
Now here's an odd thing, normally I'm pretty observant and thorough when I do a job, but this time I noticed that the entire surface of the ABS PCB is covered in a kind of clear jelly stuff, and it was clear that when I'd been in there before I had not removed this from the part of the PCB that I want to work on. How on earth I thought that I'd be able to solder properly with this jel on I have no idea, I must have had my stupid hat on that time. So this time I removed the jelly stuff, made sure it was scrupulously clean with a stiff brush, and had another go at re-soldering. This time I used an illuminated magnifying glass on a stand (courtesy of my wife's sewing equipment - thanks love) which helped see exactly what I was doing. Now I'm not sure, but I do think that I could see small rings of cracked solder around some of the pins, and what's more they were in the vicinity of the rear sensor feeds which ties up with the codes I've been getting. I did them all anyway, with particular attention to the main power feed pins, and put it all back together again. By the way to answer a previous question, yes, the pins are clearly numbered in the black plastic socket, so quite easy to know where you are with them.
I also removed and cleaned the main battery to body earth point as it looked a bit crusty, but I'm not sure this will have had anything to do with my fault.
Took the car on a decent test drive, and no lights so far. It's way too early to tell of course, but at least I know I haven't introduced a fault with some cack-handed soldering or some other silliness, so that's all good.
Previously it was putting the light on every other journey or so, so hopefully in a few days I can build some confidence that it's fixed, I've still got this horrible feeling I'm going to be back on here before long saying the light's back on, but so far so good, time will tell - that's the problem with intermittent faults isn't it?
Not too hard a job to do by the way, slightly skinned knuckles getting the old unit out (removing the air box helps a lot). Important to have the correct Torx socket, and a tiny 1/4" ratchet head was invaluable too. Also useful was use of an LED head torch - mind you, that's useful for pretty much any job I reckon. The illuminated magnifying glass helped a lot too, plus the usual spadefuls of patience and time.
Thanks all - I'll post back with how it goes of course
