Code 0171 Check Eng light
 

Hi, My hummer H3, (2007) is displaying code 0171. We already change the oxygen sensor and the MAF sensor but the light is still on. What I can to to solve the problem. Just to let you know that I used AC Delco parts only.

I really appreciate all support with it

I am pretty sure there are 2 oxygen sensors, 1 on each side of the Cat. Someone correct me if I'm wrong. Maybe you changed the good one.

For the H3 a code P0171 may mean that one or more of the following has happened:

There could be a vacuum leak downstream of the MAF sensor, a possible cracked vacuum or PCV line/connection;

The MAF Sensor is dirty or faulty,
[The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.];

Failed or faulty oxygen sensor (bank 1 since I5s only have one, sensor 1=upstream);

Sticking/plugged or failed fuel injector;
Low fuel pressure (pump going bad);and,
Exhaust leak between engine and the upstream oxygen sensor (I5s are known to break exhaust manifold bolts).

Possible Fixes
Most of the time, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem, but not always.

So, other possible solutions include:

Clean the MAF sensor. It is best to invest in a can of MAF cleaner and use it. Make sure you are careful not to damage the MAF sensor so DO NOT TOUCH THE SENSOR ELEMENT, and make sure it's dry before re-installing for start up;

Inspect all vacuum and PCV hoses, replace/repair as required;

Inspect all hoses and connections in the air intake system, check that the clamps are snug and in proper position;
Inspect and/or test the intake manifold gasket for leakage, they too can have loose bolts causing a leak; and,
Check for proper fuel pressure.

Best way to figure out the problem is to monitor short and long term fuel trims using an advanced scan tool so you can see what the O2 sensors are doing.

Just got done dealing with the same code for two months.
Here are my two posts dealing with the issue and my findings:

Dealing with the same issue with my 06. But mine is to the point that it is not very drive-able. Did some messing with it yesterday. Pulled TB and inspected and cleaned (it was in great shape), checked the whole intake system for vacuum leaks all looked great. Reassembled and took her for a drive, same issues, runs fine if you can get it to go from the stop sign, but idle is rough and stumbles hard from a stop. Ran compression test after the short drive all 5 up over 200 psi. Fuel pressure good. New MAF. No codes. But I did notice when I pulled it in the garage a had a strong gas odor when I shut it down and re inspected the intake system. I am thinking a injector is bad in my case, node signal is good to all five, just think I might have one sticking. Other things that I have found: When running fuel injector cleaner (Techtron) she runs great, have not used it in the last few tanks. Also when I shut the vehicle off I get a little pop out of the intake (4 out of 5 times). I am going to put in a new set of injectors and plugs next weekend, along with reseal the intake and see what happens.
Will keep you a breast of the out come. Pete


Well pulled things down this weekend. 2 hours of pulling battery box, harness's, fuel lines, alternator, tire, wheel well and intake. Not that bad of a job. One thing I noticed after getting some stuff out of the way, I was able to wiggle my intake manifold (have not pulled any bolts yet). Further investigation I found the first 3 manifold bolt were half way out (gas smell on shutdown, lean bank one code?). Once I started to remove the remaining bolts it only took my socket in hand to do so, they were all loose. Pulled the intake, all seals were in place but very sooty. Figured I have new injectors in hand, so what the hell mine as well replace them, I am already there (plus I have 104,000 mile on it). Cleaned all ports lubed injectors and installed, then installed the rest all in the reverse order. The little truck never ran better and no codes!
Highly suggest that everyone go give your intake manifold a wiggle, it will move a little, but should not move excessively. Bolts are a little work to get at but a check on them would be a good idea if you are having any Bank One Lean Codes or hesitation of idle issues. Wish I took photos for you all but once I dug in I was committed. Pete

Today a 0171 appeared. Few things were done under the bonnet, so probably service spoil something.
MIL appeared only on idle RPM's.
I did about 2000 miles untill today, MIL never appeared, today after cancelling it, returned few times. For me it's unlikely coincidence that oxygen sensor died exacly during service procedures. I bet they messed up something with vacuum and did not admit to. Am i right? Where to start looking for leak?
H3 07 less than 35000miles

Make sure the lil black hose under resonator box for intake is not dry rotted or missing loose.

Chris