The code P0155 refers to a malfunction in the oxygen (O2) sensor heater circuit for Bank 2, Sensor 1. This particular sensor is usually located on the exhaust manifold or the front section of the exhaust system.

The oxygen sensor plays a crucial role in determining the air/fuel mixture in the engine. It measures the amount of oxygen in the exhaust gases and sends this information to the engine control unit (ECU). The ECU then adjusts the fuel mixture accordingly to ensure optimal combustion and reduce emissions.

The P0155 code indicates that there is an issue with the oxygen sensor's heater circuit, which is responsible for quickly bringing the sensor up to the correct operating temperature. The sensor's heater element helps it reach the proper temperature faster, especially during cold start-ups.

When the ECU detects a fault in the heater circuit, it will trigger the P0155 code and turn on the Check Engine Light. There could be several reasons for this code, including a faulty sensor, a problem with the wiring or connector, or a blown fuse.

To diagnose and repair the P0155 code, here are a few steps you can take:

1. Visually inspect the wiring and connector leading to the Bank 2, Sensor 1 oxygen sensor. Look for any signs of damage, loose connections, or corrosion. Repair or replace any damaged components as necessary.

2. Check the fuse related to the oxygen sensor heater circuit. If the fuse is blown, replace it and retest to see if the code returns.

3. If the wiring and fuse are in good condition, it may be necessary to replace the Bank 2, Sensor 1 oxygen sensor itself. Keep in mind that the specific location of this sensor can vary depending on the make and model of your vehicle.

Ensure that you select a high-quality replacement sensor that is compatible with your vehicle's engine and emissions system.

4. After replacing the oxygen sensor or making any necessary repairs, you will need to clear the trouble codes stored in the ECU using a diagnostic scanner. This will reset the Check Engine Light.

5. Test drive the vehicle to see if the code returns. If it does not, this indicates that the repair was successful. However, if the P0155 code comes back, further diagnosis may be needed to identify any additional problems.

It's important to note that troubleshooting and repairing automotive issues can be complex and may require professional expertise. If you are unsure or uncomfortable performing these steps on your own, it may be best to consult a qualified mechanic. They will have the necessary tools and experience to accurately diagnose and fix the problem.