Toyota Echo 2003 Check Engine Light Flashing: Pre-Cat O2 Sensor Issue?

Hello, I'm having a check engine light issue with my 2003 Toyota Echo. The yellow check engine light is on and occasionally flashes while driving, especially at low speeds. I've checked the engine but don't have much mechanical knowledge. I'm wondering if my pre-cat O2 sensor has failed or been damaged. Can anyone confirm whether a faulty pre-catalytic converter oxygen (O2) sensor could cause this symptom? Any advice on how to diagnose or replace it would be greatly appreciated. Thanks for your help!