We're getting "check engine" messages more frequently now that read "O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)." I assume this means (a) time to replace the sensor, and (b) it's the before-catalyst sensor. Yes?

Some questions:

1. There's a $65 difference between the OEM from eEuroparts and the generic Bosch sensor from "alloemvolvoparts.com". I've used generic sensors for a while on my 1987 740 and 1982 240, and they've been fine. I will admit the four-wire sensor's looking a bit more intimidating, though. How easy is it wiring a generic one?

2. The eEuroparts listing says, "Must also use updated harnesses 9202714 (x1), and 9202715 (x1)."

3. When I look down from the top, there's a sensor visible sticking out of the exhaust pipe right down there the pipe disappears under the body. Is this the front one?