[size=3]I have a 2002 Blazer LS 4.3L 4wd 65k miles.....

Check engine light has been on for a 6 weeks.
Disconnected battery overnight twice but does not clear.
Advance Auto Parts Global OBDII scan says P0155- O2 sensor heater circuit malfunction (Bank 2 Sensor 1)
Bought sensor from Advance Auto but connector was wrong (Bosch).
Which sensor is bad?

Please help!

Tom

 

Do yourself a favor and purchase an AC Delco sensor. Bosch sensors are JUNK!

B2S1 is the passenger side O2 sensor directly before the 'Y' in the y-pipe.