Bank 1 sensor 1 is closest to the firewall and located just below the exaust manifold.
Easiest to change from under car.
Mitsubishi Galant, 2002, 4-cyl, O2 sensor, bank 1 sensor 1 (upstream)... PART NUMBER: MR506364
There is no bank two on this van.
Bank 1 is the pass side.
Yes.
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 Sensor 2 is the sensor AFTER the catalytic converter. Causes could be,A faulty O2 sensor, Exhaust leak near the sensor, Damaged catalytic converter, Damaged wiring to O2 sensor,
The rear cylinders are 1-3-5 so that is bank 1. Front cylinders are 2-4-6 so that is bank 2. Follow the exhaust pipe from bank 2 and you will find the O2 sensor.
The bank 1, sensor 3, O2 sensor would be the O2 sensor post cat.
Passenger side and after the catalytic converter O2 sensor.
O2 sensor circuit low voltage (bank 2 sensor 1)
Passenger side exhaust pipe directly after the exhaust manifold.
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