Ive got the 2005 nissan quest 3.5L se 128000 i have changed the plugs with Nissan plugs the fuel economy keeps getting worse there's no mil light on but have notice on my scanner that the two upstream afr sensors not responding normally with snap throttles and carb cleaner being in the air duct,the are both bios lean,long term fuel trim 9+ and short term fuel about 4+ meaning the pcm is adding fuel,but there are no vacuum leaks. Im going to purchase two new Nissan afr sensors they are bad.if anyone has done this procedure i would like to hear from you,for the b1s1 i have looked through the passanger side wheel well,but not good for the angle it is,please let me know thanks.

Check the rear O2 sensor first. This has be an issue on Altima, Frontier and some Rogues with the QR25DE 2.5L. I hear it throws a code for the AFR but it's actually the result of of an aft O2 sensor failure. Don't know if it could even be an issue with the 3.5 but may be worth a look.