Q: whats the difference between an upstream front and a upstream rear?

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I have an 2002 Toyota Camry V6 that has a error code p1150. I was told that its my bank 2 sensor 1 and it needs to be replaced. Now because its a sensor 1 its a heat sensor, so they're more expensive. I've been shopping around looking for the cheapest piece. Theres this one website that sells it for cheap but the language they use is different and its confusing me. I thought that upstream and downstream describes whether its before or after the catalytic converter. But It lists the sensors as upstream front and upstream rear. Could you tell me what front and rear is referencing exactly?

My car has 130000 miles.
My car has an automatic transmission.

Hi there - your understanding and terminology oxygen sensors - "upstream" and "downstream" are correct - upstream is between the engine and (before) the catalytic converter. Downstream is after the catalytic converter. I would be suspicious enough of a parts website that doesn’t have clear language to NOT buy from them. I would recommend an oxygen sensor replacement by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.

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