Check engine light still on a 2004 Silverado

[Hookmaster]

In another post I thought a loose gas cap was the cause but the check engine light is still on after a week. Pulled the codes and there were two.

P0171, System too Lean, bank 1

I googled it and one hit said to clean the mass air flow sensor. What do I clean it with and where is it. I'm sure I can do the work but don't know where it is. Never cleaned one before, do I need to treat it with a penetrating oil before taking it out?

P0131, O2 Sensor Circuit Low Voltage, Bank 1 sensor 1

Auto parts guy said to take out the O2 sensor ahead of the catalytic converter and clean it. Is this location correct? Clean it with what or just replace it? Never took one out before, do I need to treat it with a penetrating oil before taking it out?

Any other ideas?

[Jeremy airjer W]

Those two codes would lead me to believe the O2 sensor has gone bad. If it where lean on both banks than "cleaning the maf" might help but would be more inclined to think vacuum leak as a starting point. The O2 that is on the same side as the #1 cylinder is the bank 1 O2. The sensor before the cat is sensor 1.

****DO NOT GO ANYWHERE NEAR THE MAF SENSOR WITH PENETRATING LUBE!!!***

You should be able to get on the O2 with a 7/8" open end wrench and have it turn out without much effort.

[Macgyver55]

Those two codes would lead me to believe the O2 sensor has gone bad.

I agree.

[Hookmaster]

How do I tell which side the #1 cylinder is on? One of the google hits said the driver's side. Is that right or how do I find out?

[Macgyver55]

Drivers side front is #1 cylinder, passenger side front is #2

Drivers side second back is #3, passenger side second back is #4 and so on.

Also when you hear o2 sensors referred to as bank 1 or bank 2

Bank 1 is the drivers side bank 2 is the passenger side.

Also with o2 sensors they may be called sensor 1 or sensor 2. Sensor 1 would be the upstream and 2 would be the down stream. They may also be called or pre cat or post cat in some instances.

[Hookmaster]

I replaced the O2 sensor for bank 1 sensor 1 on Tuesday and the check engine light went out on Wednesday. Thanks for all the help guys. The sensor came out of the tail pipe fine, 7/8" just like airjer said. The more difficult part was getting to the wiring harness. Had to snake one arm around the tail pipe and something else to get at it. My forearm is still a little sore where it was rubbing against an edge.

[jwhjr]

Good to hear you got it taken care of. Thanks for the update.