I got the PO154 code flash up today which is the O2 sensor, but my question is how do I find out if it is the upstream or downstream sensor?

 

What does it say in the code description? Bank1 Sensor2 (B1S2)?

Bank 1 is the drivers side of the motor, bank 2 is passengers side. S1 or sensor 1 is upstream, while S2 sensor 2 is down stream, normally after the cat.

 

Thank you. I'll have another look.

 

Anytime. Keep us posted.

 

P0154 is bank 2 sensor 1, (B2S1). Upstream sensor on the right side of the vehicle. That would be the driver side of your RHD, (Right Hand Drive) Blazer.