2001 LS430.
Just changed both heads.
was getting code for engine not warming up fast enough.
using scanner:

Oxygen Sensors:
BANK/SENSOR. IDLE. 3K RPM
B1S1. 0v. 0v
B1S2. .915v. .835v
B2S1. .565v. .250v
B2S2. .800v. .740v

so obviously B1S1 is dead.
but I assumed that since it was showing zero volts vs any voltage, that a wire or 3 was disconnected.

first step, I removed the O2 sensor. Either by doing so, or previously, all wires were pulled out of the car-side plug.
So I extended the wiring and taped up the exposed wiring areas on the O2 sensor itself (new one on order)

I put it all back together and now I am getting:

B1S1. 1.275v
B1S2. 0 v

wtf?

anyone know what this means? Reving up the engine gives me 0.015v on Sensor 2 but only momentarily.