I'm leaving on a 800 mile trip tomorrow and check engine light came on. Took it to autozone and computer said it was the o2 sensor. Is this something that should be replaced prior to the trip or can it wait?
I agree with the others it's hard to start anywhere without knowing the exact code that was set.
Even it was an O2 sensor code that doesn't always mean the O2 sensor is faulty, often there are other issues that affect the O2 sensor performance which cause O2 sensor codes which are often misdiagnosed.
If it was an O2 sensor code relating to range/performance you would then test the sensors under different conditions to see if they are actually faulty and also read the live data in the engine to identify any other potential issues.
Without known the exact code you got, it is impossible for us to gauge if this is an issue or not. For example, if its the heater circuit, then you will probably be OK. If the sensor is measuring rich the whole time, then you will probably not be OK (the catalytic converter could overheat and internally melt/get plugged).
Given that typically cars these days have two O2 sensors, there is some level of redundancy. Also, do note that the car when warming up operates in an open loop mode. The absolutely worst that could happen is that your car continues to operate in an open loop mode even when warmed up. It may mean worse fuel economy and possibly higher emissions.
So, if you ask from Greenpeace, they will probably say that the car should not be driven. But my opinion is that you can perfectly well take the trip and replace the sensor when you have time for that.
The O2 sensors do a couple of things each. The one above the exhaust is there to tell the CPU, that the air/fuel mixture is perfect and can only work with the ambian temp from the sensor in the water jacket and the Mass air flow sensor in the intake. The MAF tells the CPU how much air is coming thru, the ambiant temp sensor tells the CPU that the engine is warm enough to run in normal mode the crank sensor tells the CPU when to inject fuel for a maximum imput and the camshaft sensor tells the CPU when to set off the spark. Now the O2 sensors tell the CPU that the mixture is perfect and the one after the exhaust checks the amount of co2 and when the ambiant temp sensor tells the CPU it's warm enough then the O2 sensor tells the CPU to open the valve between the positive Crankcase Ventilator and the intake manifold to burn the excess gas. Until it's warm enough then the excess gas goes into a carbon filled tank which holds the gas until it's warm then the O2 sensor tells the CPU to open it up and the car... Runs great . I would not like to have my engine turned into a stationary engine, and that is basically what happens when the CPU doesn't get the signals it needs. It keeps putting the engine into start up mode. Then you get to take it to a dealership to get the CPU reset. $1,700.00 is about what it was when I worked for one. I was just a tow truck driver.