A few months ago I had to replace my O2 with a universal Bosch sensor. And it works perfectly.
The other day I was at Orileys and they had a sensor laying on the counter. I noticed the blue and black plug on the end of it. I knew it looked really familiar. So I carried it home and bingo.... I checked it against my original O2 sensor and it was a perfect match. It's a heated 4 wire O2 sensor. With the correct pinouts.
It is a Bosch 16746 and it fits a Cadillac SRX or CTS or STS 2005 and 2006.
And if you look on amazon I have found them for $31.40