P0155 - 2/1 O2 SENSOR HEATER FAILURE
The first oxygen sensor in cylinder bank #2 is numbered O2 Sensor 2/1.
So, to simplify it's location, bank #2 is the side of the #2 cylinder or in the case of your vehicle, passenger side.
Sensor #1, is the O2 sensor forward of the catalytic converter.
Check ALL fuses and wiring to the O2 sensors. Make sure the connectors are good and not damaged.
O2 sensor heater feed circuit open
O2 sensor heater ground circuit open
O2 sensor relay
Fused B+ output circuit open
O2 sensor heater relay output circuit open
Short to ground between relay and fuse
Wiring harness intermittent problem