 Tips to identify on O2 sensors bank location.
We are constantly getting Ford hotline calls about repeating oxygen (O2) sensor codes. Often, the technician has replaced the O2 sensor, sometimes more than once, only to have the code return.
Most of these calls revolve around identifying the location of the O2 sensor by the code. All OBD-II Ford 4-cylinder engines have two sensors: 1-1 and 1-2. On V engines, there will be two, three or four sensors: 1-1, 2-1, 1-2 and on some with dual exhaust, 2-2. The first digit in the number is the Bank ID: 1 = bank 1, 2 = bank 2. The second digit is its Location ID: 1 = close to the exhaust manifold, 2 = behind the CAT.
On all OBD-II Ford engines, Bank 1 is where cylinder No. 1 is located. On rear wheel drive, this is the passenger side of the vehicle, and on front wheel drive, it is the bulkhead (firewall) side of the engine. The driver's or radiator side of the engine is bank 2. So if you get a code for 2-1 on a V-8 pickup, that would be the driver's side front sensor. Or a 2-2 on a V-6 or V-8 Taurus would be the back sensor for the radiator side of the engine. Make sense? | 
