E32-740il
02-04-2007, 07:13 PM
My check engine light came on with a code 1221, which corresponds to oxygen sensor for cylinder bank 1 according to the code list I reviewed. There is a different code, 1212, which is for cylinder bank 2. I received only the code 1221 for cyl. bank 1. I assumed that cylinder bank 1 is for cylinders number 1-4, or the passenger side of the V-8. Therefore, I assume the O2 sensor in the passenger side exhaust pipe is the one that generated the code. When I went to change that sensor, I noticed the sensor on the other side (driver's side exhaust) had a patched gray wire (the ground wire.) I changed the pass. side O2 sensor anyway, disconnected the battery for a while to reset the check engine light, and started the car. I let it warm up to full operating temperature so it was operating in closed loop at that point, and got no check engine light. I am not sure if I replaced the correct sensor - perhaps the patched ground wire on the driver's side got wet and caused the fault code - does anyone know whicn O2 sensor would be at fault - passenger or driver side exhaust pipe - to generate a code 1221? Am I right with my "logic" that cylinder bank 1 would be cylinders 1-4 or the passenger side of the car? Thanks!