oxygen sensor

I went to autozone today and had my SES light scanned. I got back 2 codes saying i had a lean condition in my left and right bank. Now I am guessing this is caused by my old spark plugs but what are the chances that an O2 sensor is causing this? Would it be both sides? The SES light is intermittent. My truck is a 2002 z71 with the 5.3. My next question is how hard are these to change? I have heard horror stories about them being terrible to get loose. How many are there on my truck? Should I change them all as I have noticed a decline in my fuel ecomony? Thanks!

I went to autozone today and had my SES light scanned. I got back 2 codes saying i had a lean condition in my left and right bank. Now I am guessing this is caused by my old spark plugs but what are the chances that an O2 sensor is causing this? Would it be both sides? The SES light is intermittent. My truck is a 2002 z71 with the 5.3. My next question is how hard are these to change? I have heard horror stories about them being terrible to get loose. How many are there on my truck? Should I change them all as I have noticed a decline in my fuel ecomony? Thanks!
you have 4 o2 sensors 2 before cat and 2 after cat. the before or upsteam o2 sensors control PCM.because both read lean my guess is fuel delivery problems have fuel pressure checked.if you what to change some parts start at fuel filter if its been over 30,000miles it could be that simple or it could be more complicated and very expensive.mileage and maintenence history is very helpful when these questions are asked.........

The truck has 217000 miles on it. I do not know the maint. history before 200000. It does have the dreaded check valve problem with the fuel pump. I was thinking it was spark knock that was causing a lean condition reading. I will start with a fuel filter and then spark plugs as those are things i should change anyway as i do not know when they were put in. thanks

The truck has 217000 miles on it. I do not know the maint. history before 200000. It does have the dreaded check valve problem with the fuel pump. I was thinking it was spark knock that was causing a lean condition reading. I will start with a fuel filter and then spark plugs as those are things i should change anyway as i do not know when they were put in. thanks
fuel pressure is critical need 55psi approx. cut open gas filter if dirty and metal particles fuel pump probably bad but fuel pressure test will show that, and don't forget the fuel rail regulator as it has many miles on it. when engine shuts down should hold pressure if not most likely internal fuel pump check valve. don't run vehicle with less than 1/4 tank of gas as this damages pump...........

Gotcha, I have been saying since I bought the truck 20000 miles ago that I would wait until the fuel pump died before I would change it. Maybe this is my sign... sounds like i need to do some fuel pressure testing. Also one thing I forgot is that when it idles sometimes it is rough and drops to maybe 300rpms, then kicks back up to 500. I attributed this to the SES light problem. the code I got was P0171 by the way. Thanks for the help, I really appreciate it!

another issue i have found was the intake manifold gaskets shrink a bit in cold weather causing this. once engine warms up all is fine, but on cold start in cold weather. for both banks to be running lean, this is one thing to check. get some throttle body cleaner and spray a bit along the intake where it meets the head on a cold start. if engine stumbles a little bit, then start with the gaskets. easy job to do.

Well I finally replaced the fuel filter and it seems to have fixed the rough idle problem. It got so bad on 2 occasions where the truck died and had to be restarted. So far so good though with the new filter. Thanks for all of the help!