2009 Toyota Matrix, 89K miles, AT. 

The A/F ratio sensor (B1S1 upstream)is constantly going up to 5V (stuck lean) then go back to normal around 3.3V. It is stuck lean only couple of seconds and go back to normal, so it doesn't always throw a CEL but it does cause the P2159 code (AFR stuck lean B1S1) once in a while ( maybe once every 1-2 weeks?). Once I clear the code manually without doing anything, the car runs about a week or two until the code comes back.   

It only happens while driving and during decel (throttle position closing) based on the scan tool live data. It stays around 3.3V when idles, which it should be. Whenever the AFR sensor stuck lean, it cause the fuel status to "open loop" instead of closed.  

I have not noticed any drivability issues yet other than the P2159 code comes back.

I checked the wiring and they seem to ok. I see 12V on the heater circuit and 3.3V and 3.0V on the sign port. 

I checked the AFR sensor responses to lean and rich condition but it seems to response to both fine. I did measure the resistance of the heater and this is what makes me confused. It varies from 2.8 to 6 ohms. The ohm spec is 1.8 to 3.4 ohms. 

Is it a bad AFR sensor? Can a bad heater cause the AFR sensor to stuck lean then go back to normal? 

Any insights would be apricated.