Engine Builders: The AERA Technical Committee offers the following information on cylinder locations for Toyota engines. This information is provided as different locations are used for the number one cylinder. This service bulletin illustrates the proper identification of engine bank 1 and engine bank 2, and the correct location of air/fuel sensors and oxygen sensors for replacement.
Bank 1 (B1) refers to the bank that includes cylinder No. 1.
Bank 2 (B2) refers to the bank opposite bank 1.
Sensor 1 (S1) refers to the sensor that is located before the catalytic converters.
Sensor 2 (S2) refers to the sensor that is located after the catalytic converters.
Failure to obtain and install the correct sensor will alter the way the engine runs as components are calibrated differently for the specific locations.