Unfortunately Chilton's Volvo book, like many of their others leave a lot of detail out. My 940T wagon check engine light came on, and the manual only indicates checking socket 2, & 6 for codes, but never mentions the "B" set of sockets on my model, and what's worse, is I can't find a match to the code in the book. Socket #2 in the "A" bank, which has the switch, show 111, which is an OK. Socket 6 on the same bank, gave me a 241 code, and no explanation in the book. On the "B" bank socket #2 gave me a 122 code, with again no explanation. I was able to reset the codes, but on a cold start up, the vehicle hunts for a moment trying to get to a flat idle. I have some suspicions on what the problem may be, but I'm not sure yet.