Thanks for the replies guys. I cleaned it just now, took under 1hr. The rears were definitely more gunked up, looked like more grease and dirt on there. The fronts were relatively clean with a bit more metal shavings on them than the rears appeared to have. I took it out for a spin and did maybe 1 mile roundtrip. I'm not sure if that's enough for the codes to clear but they didn't. Either way I'll be driving to work tomorrow anyway so we'll see.
I was really worried that it wouldn't pass the state safety inspection but lo-and-behold, the service advisor at the local place says the ABS and airbag lights being on will still pass a safety inspection (ironic?). So I've booked it in anyway and will continue to work on the prob. When I get the PA Soft i'll diagnose and post a resolution.