On a Ford Expedition :
Bank 2 is the drivers side of the engine
Sensor 1 is between the engine and the catalytic converter ( upstream )
You did not specify which O2 sensor it is. Is it sensor 1 bank 1, sensor 2 bank 2, sensor 2 bank 1, or sensor 1 bank 2. There are four O2 sensors on a mazda 626
Is this bank 2 sensor 1 or sensor 2?
P0137 = O2 sensor circuit low volts (bank 1 sensor 2). Could be a faulty B1 S2 O2 sensor.
P0130 = O2 sensor circuit malfunction (bank 1 sensor 1) P0150 = O2 sensor circuit malfunction (bank 2 sensor 1)
Bank 2 is passenger side. O2 sensor 1 is threaded into the exhaust system between engine and catalytic converter.
Bank 1 sensor 2 would be the sensor after the behind the catalytic converter.
O2 sensor circuit bank 1 sensor 2 no activity. Check the wiring and connections to bank 1 sensor 2 O2 sensor, if all looks good replace the sensor.
Bank 1 is the side that cylinder 1 is on, sensor 1 is downstream and sensor 2 is upstream
That would be the O2 sensor after the catalytic converter.
P0155 = O2 sensor heater circuit malfunction (Bank 2 Sensor 1). All O2 sensors are threaded into the exhaust system at various points. Bank 2 would be the bank of cylinders that does not contain the #1 cylinder. Bank 2 Sensor 1 would be the first O2 sensor leading from bank 2 of the engine.
bank 1 is drivers side down stream o2 / bank 2 is drivers side down stream o2
Bank 1 is the bank that sits closest to the front of the vehicle. Bank one is the bank with cylinder # 1. You have 4 oxygen sensors, (bank 1 sensor 1, bank 1 sensor 2, bank 2 sensor 1 and bank 2 sensor2). Follow the exhaust from the head of bank 1. The first sensor you come to is sensor 1, the second is sensor 2.