Do your reverse lights work? If they don't, the pnp switch isn't lined up exactly right, and the code will stay. If they do, you probably just haven't reset it. I've modified Volvo's way because it didn't work for me, this is what I do.

Key in on position, A1, button down for three seconds, read the code, button down for three seconds again, read the code. If you got the same code on the second read, that is the only code you have in the system. If you got another code, hold the button down for three seconds again, read the code. You do this until you repeat the first code you started with. After doing this, hold the button down for seven seconds, let up, when the light comes back on, quickly hold the button down for another count of seven. Now check the code...hold the button down for three seconds...you should get 1-1-1. Now, stick the probe into A2 because sometimes the code will also show up here, do the same read and erase thing. Let us know,

Chris