I just recently bought a hummer h2. it was throwing a code for high voltage in bank 1 sensor 2. came to find out someone had cut the bank 1 sensor 2 wire. i spliced and hardwired it back into the connection and am getting proper voltage. the real issue is now that i have done this i’m getting a p0171 code. not once did it ever run this code before i wired it back in, and yes i did the wires correctly. i do have an exhaust leak before the upstream sensor. one at the manifold and one at the flange, but like i said it never threw the code even with that leak until after i wired the downstream o2 back in. what could be causing this? my MAF sensors reading correctly and ive checked every vaccum line i could check to no avail. i’m getting horrible HORRIBLE fuel economy which yes ik its a hummer with the 6.0, but its like 5-8 mpg. LTFT stat at 19.5 when idling, then drop to 11.5 under load. start stay around 2.5 then drop to 0 at idle. any advice or solutions would be greatly appreciate.

 

the manifold air leaks would probably trigger a cat inefficiency code. i would check your fuel pressure at the rail. should be about 45/50 psi. your LTF's indicate it needs fuel. maybe your intake gaskets are letting in air on the bank calling for more fuel try snugging the intake bolts on that side. if it is an 03 there is a replaceable fuel filter near the B pillar.
if the rail pressures are good and the intake does not have leaks then you need to further your search.... clogged injectors or maybe bad plugs, coils or an out of spec ignition wire. but most likely fuel delivery or bad intake gasket sealing.

 

Nice work getting the o2 back on line, now you need to repair the exhaust leak to eliminate the code!

 

did you look at the FT's prior to fixing the sensor and if so what were they, if not disconnect the sensor and see what they do.

Neal

 

I didn’t check them prior since it didn’t throw the code at all. whenever i unplug the 2nd 02 (the one i wired back in) it runs better and only throws a code for the o2 heater circuit. it honestly baffles me, with the 2nd 02 it throws lean code, without it it just throws code for heater circuit. fuel trims still stay high, but i have the battery disconnected right now to hopefully reset fuel trims.

 

that’s my next plan of action, i’m just resenting doing it because of how much of a pain they are, i don’t have access to a welder to get the ones that are snapped out.

 

just checked after resetting fuel trims with 2nd o2 unplugged still getting 25% at idle and goes down with acceleration.

 

According to Mitchel DIY, of over 60 reported repairs for the P0171 DTC, the 2 top causes are the Mass air flow sensor and the O2 sensor as long as there are no other DTC's.

I agree with HUMMERZ fix your exhaust leaks then re-evaluate, there is a list of possible causes with fuel injectors being number 3

do the O2 sensor MV's swing high and low while idling?

Check the air inlet tube and make sure the lip where it slides over the throttle body and the Mass air flow sensor is not folded under allowing the air inlet track to let unmetered air into the intake.

Neal

 

When I purchased my 08 a few years ago I was getting a code. I think it was a lean code, if I remember correctly. I was going over stuff and found the air filter was extremely dirty. I also had an exhaust leak in the exhaust manifold (broken bolt). I changed the filter and no more code. CRAZY. It worked tho. Good luck, lol, that's all I got, hope it helps someone.

 

do the O2 sensor MV's swing high and low while idling?


most i seen was 0.850 and lowest i seen was 0.090.