P0155 indicates a malfunction in the electrical heater circuit of the upstream oxygen sensor on Bank 2 (the engine bank opposite cylinder number one). The heater element brings the sensor to operating temperature quickly so the powertrain control module can enter closed-loop fuel control. When the sensor heater element, its wiring, or the control signal fails, this code is stored.
The internal heater inside Bank 2 Sensor 1 has burned open or shorted, preventing the sensor from reaching operating temperature quickly.
The power or control wires to the sensor heater may be broken, chafed, or shorted to ground or battery voltage between the sensor and the control module.
Moisture, oxidation, or spread terminals in the sensor electrical connector can increase resistance or interrupt current flow to the heater.
A blown fuse supplying voltage to the oxygen sensor heater circuit will disable the heater; this may affect one or multiple sensors depending on circuit layout.
In rare cases the powertrain control module may fail to provide the heater ground or control signal, but this should only be considered after the sensor and wiring have been thoroughly tested and ruled out.
Generally yes. The heater circuit fault does not typically cause drivability problems, though the engine may run slightly richer during cold starts and emissions will be higher until the sensor reaches temperature.
The sensor itself is the most common failure, but inspect the wiring and connector first because a harness fault can mimic a bad sensor and will ruin a replacement.
No. PCM failure causing this specific code is uncommon. Most P0155 cases are resolved by replacing the sensor or repairing wiring. The control module should only be suspected after the sensor, fuse, and entire heater circuit have been electrically verified.
Bank 2 is the engine cylinder bank that does not contain cylinder number one. Sensor 1 is the oxygen sensor located upstream, before the catalytic converter on that bank.