What does the P1155 code mean on a 2001 Toyota RAV4?

The P1155 code on a 2001 Toyota RAV4 indicates a problem with the air-fuel ratio sensor, specifically that the sensor signal is out of range or not functioning correctly. This sensor is responsible for monitoring the air-fuel mixture to optimize engine performance and emissions. Common causes for this code include a faulty sensor, wiring issues, or exhaust leaks. Addressing this code typically involves diagnosing the sensor and its related components to ensure proper operation.