My car is throwing the following code:

P0037 Bank 1 Sen 2 Heater Circuit Low

I am aware that this is a bad O2 sensor.

Does anyone know if this is the sensor located prior to the cat or post cat.? My understanding is that if it is post cat I am OK to run a while. If it is pre-cat it may cause the car to run too rich.

 

It is the bad one.
That may affect the way the car runs as well.

 

I have not noticed the car running badly at present. My mechanic suggested running the car until I noticed a decline in fuel mileage. Is this good advice?

 

That will be fine.