OBD Code P0171 and 0174

[jayshay]

I'm currently stuck in Iraq, when I was home on leave I bought a used 02 Silverado, 5.3 V-8, 4-wheel drive. I took it to a muffler shop and had them put on a set of flowmaster dual exhaust. Now, three months later my wife is having problems. She said she was driving the other day when the truck cut out and lost power, made some loud noises under the hood, sputtered, then kicked back in and continued driving. The check engine light came on. She took it to the shop and they told her it was these two codes, and said it is usually the O2 sensors. I looked at other posts on this subject talking about the ??knock sensors?? and a MAF sensor. Is the Mass air flow sensor different than the O2 sensor? Also is it possible that the new exhaust might have a leak that is causing the problem? I am going back home next month, will it be ok to continue to drive till I get home to fix, or does she need to take it to a shop? Any help on this would be great, I am not the best mechanic, but I like to try to fix things on my own.

[Airjer_]

Both sides lean usually indicate a significant vacuum leak. It is possible that the maf is dirty and registering less air flow than there is which can cause a lean condition as well. The O2's can be stuck lean as well. None of these conditions is unusual for these vehicles.

The MAF can be cleaned with some MAF sensor cleaner. It is the part right after the airfilter with 4 or five wires going to it. The sensors are in the air snorkel.

If the O2's are stuck lean they can be unplugged which will default a center value. This will usually significantly change engine performance wich lets you know you are on the right track. If there is no change it is likely not the sensors causing the fault.

If you suspect a vacuum leak they can be quickly found with a smoker. It is really common to have the intake plenum gaskets leak on these. The symptoms usually show up when the vehicle is cold and go away after the vehicle has warmed up.

[777stickman]

1st thing I would suggest is to clear the codes. It may have been just a glitch. If the codes come back then you'll have to look into it deeper as previously posted.

To answer a couple of your ?'s: NO the MAF and O2 sensors are not the same thing. The MAF, as stated, is in the intake system between the air cleaner and throttle body. The O2 sensors are in the exhaust system. YES an exhaust leak can cause one or both of these codes.

[j cAT]

with both O2 sensor codes bank 1/2,, I would suspect the intake leak as the engine has problems running correctly...

this should be repaired soon...

the chances of both sensors on each side of the engine failing at the same time would be not common...

exhaust leaks will cause dtc's but not these...

the MAF being defective is possible,,but on these vehicles the intake gasket is usually this failure with the lean condition...

[777stickman]

Originally Posted by j cAT

exhaust leaks will cause dtc's but not these...

Step 5 in the trouble shooting guide for both these codes has 10 items to check. The very 1st one is to visually and physically check for exhaust leaks.

[j cAT]

I forgot to mention fuel pressures low,,,restricted fuel filter,,,air hose to throttle body leaking after MAF....could be alot of things..

[j cAT]

Originally Posted by 777stickman

Step 5 in the trouble shooting guide for both these codes has 10 items to check. The very 1st one is to visually and physically check for exhaust leaks.

I would agree if this where 171 OR 174 DTC,,,,,IN this case he has both 171 AND 174,,,,IT WOULD BE VERY UNLIKELY THAT THE ENGINE HAS AT THE SAME TIME BOTH EXHAUST MANIFOLD'S LEAKING...ON EACH SIDE...

[kahjdh]

Warped plastic manifold, just replace one on an escalade today. Does it run noticeably rougher when cold or in the morning?

[Airjer_]

You've had them warp?

[kahjdh]

oh yea, We tried gaskets in the past but they warp. Dorman makes a set that comes with an updated manifold and all of the gaskets. We dont even replace the gaskets anymore, everthing gets an intake.

[Airjer_]

Interesting! I have not run into that yet but I won't second guess that possibility! Thanks for the tip.