2002 Toyota Avalon 3.0L V6: Persistent P1135 & P1155 OBD2 Codes - Sensor 1 Issue Diagnosis

I own a 2002 Toyota Avalon XLS with a 3.0L V6 engine. I recently encountered persistent OBD2 fault codes P1135 and P1155, which indicate issues with the oxygen sensor heater circuit for Bank 1 Sensor 1 and Bank 2 Sensor 1. I was advised that the problem lies with Bank 1 Sensor 1, so I replaced the sensor with a Denso part number 234-9021. During replacement, I checked both the old and new sensor heater resistance — they both read approximately 1 ohm, which is within normal range. After installation and resetting the ECU, the check engine light reappeared with the same P1135 and P1155 codes. I verified that the AF sensor relay and fuse are functioning correctly and replaced the relay with an identical part number. Voltage testing at the heater circuit showed 9.5V on Bank 2 Sensor 1 — is this reading normal? Using ELM Scan 5, I observed no signal from Bank 1 Sensor 1 or Bank 2 Sensor 1 during diagnostics. Only Bank 1 Sensor 2 provided a reading. Additionally, when the codes are reset and the engine is cold, it takes between 5 to 10 minutes for the check engine light to illuminate. On some drives, after traveling about one mile, the light turns on. However, once the engine reaches operating temperature, it typically activates within about one minute. I'm seeking expert advice on whether this behavior indicates a faulty sensor, wiring issue, or potential ECU problem. Any insights would be greatly appreciated.