2002 Chevy throwing codes P0171 & P0174

[Aldon73]

My 2002 Chevy Silverado 1500 with a 5.3 keeps giving P0171 & P0174 codes. It says bank 1 and bank 2 running lean. How can I fix this problem?

[davester]

There are all kinds of things that can cause this.

 

Maybe first check that all the bolts are present in both exhaust manifolds, as they tend to break off.

[Jsdirt]

Could be intake manifold gaskets, bad fuel pump,  a MAF problem, or a large vacuum leak, like a ruptured brake booster, or the hose going to it. Those codes mean it's affecting both banks, whatever it is, so that should give you some direction. Chances of both o2 sensors failing at the same time are slim, but it's worth a visual inspection to be sure the wires of both aren't melted to the exhaust anywhere.

 

A spray bottle of water is pretty good for finding intake gasket leaks - you'll hear the water getting sucked into the break in the gasket. Best time to check that is early in the morning when the engine is ice cold - it will leak worse when cold -expansion from heat can sometimes completely seal it back up.

 

Watching your short term fuel trims on a scan tool will help as you're spraying - any downward (numerically) change means you've found the leak. I suspect your trims will be around 15% or higher. If they are high at idle, cold, and improve with RPM or  heat, that's probably intake gaskets. If they're good at idle, and get worse with RPM, that's a MAF problem.

 

Some good tests: At wide open throttle (have a buddy hold and read the scan tool) the o2 sensors should be pegged rich (.8v or so) - if they're lean, you've got a fuel problem, or MAF problem (dirty, possibly). 

 

First thing I would do is hook up a fuel pressure gauge - should be around 55 psi, and the needle should spike upward on a snap throttle. If it's low, or spikes downward, you've got a clogged fuel filter or weak pump.

[muddkatt]

To add to the comments above, if you have a fuel pressure issue, be sure to change the in-line fuel filter before  changing out a fuel pump.

[Armo325]

As several folks have mentioned, there are a number of possibilities that could be the culprit.  That said, I had the EXACT same problem on my 2005 Tahoe with the 4.8.  I cleaned everything but that didn't do it.

 

I didn't do a great job with the troubleshooting and started swapping the hard-to-get-to parts parts first.  I figured since I had cleaned the MAF sensor and checked for leaks, it must have been deeper in the motor.  I changed the intake gasket and knock sensors (only because they're easy to get to with the intake manifold removed) but still had the problem.

 

In the end, the problem was the Mass Air Flow Sensor.  I bought a new one from Amazon (reminder: I had the 4.8L motor. The 5.3 might have a different part) and the problem was fixed.  It turns out cleaning the MAF sensor wasn't enough.  There was a problem internal to the sensor that was causing the codes.  A new one did the trick.

 

Good luck and keep us posted.

[Aldon73]

It turned out to be upper intake gasket leak. Thanks for all your advice on my problem.

 

[Jsdirt]

Glad you got it figured out. Thanks for the update!