Bank 1 = Right side of the exhaust Sensor 1 = the first 02 in line before cat. Sensor 2 = the last 02 in line after the cat. Bank 2 = Left side of the exhaust Sensor 1 = the first 02 in line before cat. Sensor 2 = the last 02 in line after the cat.
P0140 code means the rear 02 sensor behind the catalytic convertor has an open circuit. It says no communication from the rear 02 sensor. The rear 02 sensor is also called sensor 2, whether it be bank 1 or bank 2. Hope this helps.
Depending on the year of the Monte Carlo the 02 sensor could be installed in several places on the exhaust. The 02 sensor screws in. You may need a special socket to remove it, just unscrew the sensor and screw the new one in.
LOCATE THE SENSOR IN QUESTION THEN WARM THE ENGINE SLIGHTLY TO MAKE REMOVAL OF THE 92 SENSOR EASIER THEN USING A 02 SOCKET OR 7/8 WRENCH LOOSEN THE 02 SENSOR AND REMOVE IT ALSO DISCONNECT THE WIRING CONNECTOR.