Regarding your answer - fuel consumption and oxigen sensor

Tuning and setting of air and fuel ratio are crucial to mileage. Another thing is brake adjustments. If brakes are partially getting applied due to faulty adjustments even if you have not applied it, then it could be a reason for high fuel consumption.

p 0300 code is for random misfires
random misfires are more from dirty /faulty injectors or low fuel pressure than anything else
have a pressure test done to check pressure regulator , filter and pump operation
use a can of quality injector cleaner or remove and clean the injectors

Under the chassis. Just near to connecting rod.

Spark plugs
Air Filter
O2 Sensors
Dirty MAF Sensor

Have you done any preventative maintenance
in regards to thoses,start there

Check the air filter and or the intake tube since I have found rags and or varmints nests built in the air intakes. Hope you find your problems. harry

If you have to ask... bring it to a mechanic. there are more than 1. some are hard to get to .

Replace the thermostat and air filter and clean the MAF sensor and throttle body. These things will help you get your car's engine running 100% again with better gas mileage, if the car's engine is running too cold, the engine will run richer "more fuel" and also a dirt air filter and MAF sensor will run the engine richer too. These are the simplest things to, to get the best gas mileage and don't for get to make sure your tire is inflated to 32 PSI. Good luck

THE FUEL MILAGE ON THAT PARTICULAR VEHICLE SHOULD BE SOMEWHERE AROUND 17MPG IF IT IS EQUIPED WITH THE 4.0L V6. ONE THING YOU MIGHT WANT TO TRY IS TO RESET THE K.A.M. ON THE VEHICLE. THIS WILL RESET ALL OF THE FUEL CURVES AND OXYGEN SENSOR PARAMETERS AND ALLOW THE SYSTEM TO RE-LEARN HOW MUCH FUEL IS NEEDED TO RUN PROPERLY. TO DO THIS YOU CAN SIMPLY DISCONNECT THE NEGITIVE AND POSITIVE BATTERY CABLES AND LET THE VEHICLE SET FOR ABOUT 10-15 MIN. AFTER THAT TIME TOUCH THE TWO CABLES TOGETHER FOR ABOUT 15 SEC. AND THEN REINSTALL BATTERY CABLES ON BATTERY. THIS MAY HELP IN YOUR CASE BACAUSE WITH A NEW OXGEN SENSOR, THE COMPUTER IS NOT USED TO SEEING THE CORRECT READING SO WHEN IT DOES GET THE READING THAT IT NEEDS, IT DOES NOT KNOW WHAT TO DO WITH THEM.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jonathan_3a3c556b4b17d1d2

Hi, your car may need a tune up, tire air presure, tire size,cloged injectors,dirty air filter, fuel filter,bad oxigen sensor, all those can affect your gas consumtion. (start by checking the easyst ones first) good luck......

Hi.
The Oxigen sensor are in diferent kind.
1 -- With a single wire. " is only oxigen sensor"
2 -- With 2 wires " is only oxigen sensor"
3 -- With 3 wires " Is oxigen and heater sensor"
4 -- With 4 wires " is oxigen sensor and heater sensor.
5 -- with 6 wires " is oxigen, heater A/F sensor" normally Nissan)

OK........Your question.
Depend of the year of your car.
But all the car they are Bank 1 or single bank. Engine in line
4 cyl . or 6 cyl. And are identified sensor 1 bank 1 and sensor 2 bank 1. S11 or S21.
But all the Engines in V are bank 1 and bank 2.
Sensor 1 bank 1, sensor 2 bank 1, S11 or S21.
Sensor 1 bank 2, sensor 2 bank 2, S12 or S22.
Sensor one is alway before catalystic.
Sensor two is alway after catalystic.

If you have problen with the oxigen sensor you need to put a scanner to see the number of code, The number of code will give the especific sensor that you need to replace.
The code can be heater or oxigen. and can be refer to a the same sensor.

I hope this information work for youu.
Thank you for use fixya.