Have you made any progress with this? One thing to point out: the system should go into closed loop a minute or so after start up, as soon as the 02 sensor has warmed up due to its internal heater and the heat from the exhaust gases. The sooner you pull away, the quicker it heats up. And the ~0.49V is a bias voltage created by the ECU that it can use, when the ignition is turned on, to detect a short to ground in the sensor. I’m not 100% certain, but I don’t think that bias voltage allows the ECU to detect an open circuit; however, it does allow you to carefully probe at the 02 connector with the ignition on, engine off, to see if you detect that voltage - if not, you have an open circuit between the ECU and the connector. It won’t be 0.49V, your digital voltmeter will pull it down, depending on its input impedance. That 0.49V bias voltage drops away to zero as soon as the 02 sensor starts to warm up and switch between ~0.2V and ~0.8V, which it should do around once a second.

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