My check engine light came on and I took my 07 Si down to the local parts store to have the code scanned, which came back as the secondary O2 sensor heater. The guy at the parts store says that he THINKS it s the O2 sensor on the downstream side but he wasn't 100%. Anyone had this issue? Why is there a heater on an O2 sensor?

 

The secondary oxygen sensor is the one past the cat, the primary is the one before the cat. The heater is there to heat up the oxygen sensor so that it gets working as fast as possible. Normally when it throws a heater code that just means the oxygen sensor is bad so replace the secondary oxygen sensor after the cat which is also called the downstream sensor, clear the code and see if it comes back. If not then you're good.

 

Awesome thank you.