07 Chevy Malibu P0133 Code issue

P0133 is B1S1. Which is the upstream oxygen sensor on the cylinder #1 side of engine. That is if it is a V6. If it is a 4 cylinder, it is the only one on top of engine. Did you replace this one?

Thank you for your quick response. I am not sure that I understand when you state "on top of engine". The sensors I know of are upstream and downstream. Before and after Catalytic converter. Is there another sensor that I am missing? By the way this is a 4Cylinder 2.2L Ecotec engine.

Since it is a 4 cylinder, you only have 1 up top. Look on the exhaust pipe coming out of engine. You should see what looks like a spark plug with a wire on it. Did you replace this one?

I have replaced both sensors, the one closer to the engine and the one farther from the engine. As I understand this is upstream and downstream (before and after the catalytic converter) Is there another one that I am missing? Here is a pic of the whole thing.

Yep so you replaced both. Do you have a scanner that gives you live data? If so, see if both are online and if one is not reading then I would check wiring up to them. With the 133 code I would be suspecting wiring going to the one before the sensor. B1S1 on the scanner. The only other thing that rings a bell is what brand of 02 sensors did you put on? Some cars do not recognize some brands. Ohms are different.

With the wires that close to the exhaust, I would not be surprised if it didn't either burn through or break inside insulation. Seen it before

There is 12V going to the sensors. Scanner does show that both sensors are working but I can't tell if they are doing what they are supposed to. I have purchased the sensors at a local auto part store. Sensors are not of the same brand. Upstream is Denso and downstream is NTK. Is there a procedure that can be done using a scanner to find out more info about the sensors activity. I have an OBD2 to usb with a software which I use a laptop for.

At this point I do not see other options but to assume that the b1s1 sensor is either faulty or not compatible. Any suggestion on the brand I should replace it with?

I would seriously consider wiring to that sensor. I had this on an Avalon

That code is specific to that sensor so it is in that circuit.

I will focus on that sensor now. Will keep you posted.

I have checked the wires around the sensor and it looked OK. After doing couple of measurements this is what I got: 12V are coming to the sensor 5.2ohms across sensor heater software shows variable voltage maxed at .8V coming back from the sensor. I understand that this isn't enough to tell if the sensor itself is faulty but I believe it is enough to say that the wires to and from are OK

There are lots of YouTube videos that explain oxygen sensor values on scanners