I also have this fault. diagnostics said it was the longitudinal sensor. There are two sensors that show as this fault, one is the longditudinal the other is the lateral.
One behind the glove box as has perviously been said. The other I believe is in the steering column.
Sadly they both show up as the same fault so you can't tell which one is the faulty one.
Anyway, like I said i've had both of them replaced. I still have the lights coming on tho. Totally at random, they come on and stay on. They clear once the engine is switch off and on.
It's very annoying to have these lights coming on and no clear answer.
I've had the car checked for faults again but nothing comes up. (it was checked when the lights were off)
My next line of thought was to get the garage to check the abs sensors when it's in for it's next service, could end up spending large sums on labour chasing this fault.