Running Lean

[gr82bCanadian]

2004 Silverado 2500 6.0L
My check engine light has been coming on and off for the last year, thought it was the gas cap, bought a new one and still having the issue, had code read recently and coming up 'running lean', to my knowledge that means its getting too much air, correct? Where do I start to find the problem?

The truck runs like a dream otherwise, only 87000KM on her, all maintenance a fluids always kept up.

What I have noticed now that we are driving it more because the Trailblazer is in the shop is the light will go out (on its own) after driving around town but as soon as we get back on the highway to come home (30 mile trip), about half way the light comes on and will stay on till we are back to city driving.
Please please help
If I can't get this fixed myself it will be the next one to the shop

 

[bore_pig]

Check your o2 sensors.

 

[gr82bCanadian]

Check your o2 sensors.

Thanks, from some other searching that was a thought too but wouldn't the code come up saying o2 sensor? Or that would be too simple for a GM vehicle lol

From my further researching, I am finding out that with a bad o2 sensor the truck will run/idle rough due to a rich (not lean) air/fuel mixture causing emissions trouble, correct me if I'm wrong please.
My truck is running great other than this light coming on (and bad fuel economy only when light is on).

 

[ScarabEpic22]

What exactly is the code?

Ive never had my TBs throw an O2 code yet when I swapped the sensors out on my 02 I gained .5-1mpg back and the fuel trims were more consistent.

 

[gr82bCanadian]

They didn't tell me the actual code # sorry

Just said it means running lean.

And does fuel economy suck (worse than usual) when the engine lights on.

 

[MAY03LT]

They didn't tell me the actual code # sorry

Just said it means running lean.

Well they're no help

There can be two lean codes, one of for each bank (Bank = side of the engine), P0171 and P0174. When I have one with a single bank running lean the diagnostics are much different then if both banks are running lean. That's why it's kinda important to know what the code is/codes are.

For DIY troubleshooting, you're limited to inspecting the vac lines/looking/listening for an obvious leak. Outside of that, diagnostic equipment is needed. Then again, I saw some guy on youtube smoke test an intake using a cigar.

And yeah, a lean condition causes the pcm to dump more fuel as a means of correction, so mpgs tank.

 

[jimmyjam]

Vaccuum leak. Look on YouTube for tips on how to hunt them down.

 

[tricguy007]

Let the truck sit overnite, then have a can of carb clean and fire the truck up and spray around the base of the plastic intake if the truck runs bad when this is done u have an intake leak and will require new gaskets

 

[gr82bCanadian]

Well an a update.....
Finally took the truck in for the check engine light, was P0174B--Fuel Trim System Lean-Bank code, but it also had a old history code for P0101B--the Mass Air Flow Sensor Performance, so the cleaned the Mass Air Flow Sensor and we are good so far fairly cheap fix so hope it was the problem

 

[The_Roadie]

Finally took the truck in for the check engine light,

Just curious - what did that cost ya? If you don't have a free service like from a parts store, most mechanics charge more for one code read than a low-end reader would be. Then you own one and can charge your buddies! (Beer or bourbon - whatever currency your wife can't spend...)

 

[gr82bCanadian]

The shop I take both our trucks to has done a few free scans for us, they did charge for the scan/diagnose/re-learn/road test/etc this time but the truck was in for more than just this issue....and....remember we pay a lot more in Canada for parts and service than you guys do in the U.S, this shop charges a flat $120 (like all shops here) for the diagnosis(s), which is basically an hour labor rate.....and then 1/2 hr labor charge to remove, clean and replace the Mass Air Flow Sensor.

We are looking into getting a code reader of our own, just not sure what to get, but when we do get one and I charge my "buddies" beer or bourbon to read.....hubby would drink it all....then I'm left with a code reader and a drunk husband not sure how that benefits me

 

[The_Roadie]

... we do get one and I charge my "buddies" beer or bourbon to read.....hubby would drink it all....then I'm left with a code reader and a drunk husband not sure how that benefits me

Wicked sorry. It totally flew over my head that you were not the beer or bourbon drinker in the family, or the wife. 1000 apologies.

Your question DOES give me an idea for a multi-purpose product, however. But it shall not be discussed in the public sections of the forum, as they are (for the most part) kid-friendly.

 

[RayVoy]

but it also had a old history code for P0101B--the Mass Air Flow Sensor Performance, so the cleaned the Mass Air Flow Sensor and we are good so far fairly cheap fix so hope it was the problem

Hi Karen, the problem is usually an air leak after the MAF, but, it could be as close as to be the seal at the MAF, maybe removing and cleaning resealed the MAF and fixed the leak.

Let the truck sit overnite, then have a can of carb clean and fire the truck up and spray around the base of the plastic intake if the truck runs bad when this is done u have an intake leak and will require new gaskets

If the leak returns, this is a good suggestion; but, a can is not always available around the house. A lot more homes will have a small propane tack, like a propane torch. Let a little gas from the torch nozzle spray around the intake, if the engine changes speed, or sound, you probably have an intake leak.

The problem can also be caused by air getting into the exhaust system, a little un-burned air hitting the O2 sensor will cause it to read lean.

 

[gr82bCanadian]

Well the dreaded engine light came back on seems more likely when there is less than 3/4 fuel in the tank. I'm going to do the carb cleaner spray test and see what happens....

Why can't vehicles be easier diagnosis, like back in the day (not that I'm THAT old) you knew what the problem was by just a funny sound

 

[The_Roadie]

Why can't vehicles be easier diagnosis, like back in the day (not that I'm THAT old) you knew what the problem was by just a funny sound

And there were few enough trouble codes that you could make the dashboard flash it at you.

 

[mshoda79]

I'm having a very similar issue with my truck. Check engine is throwing that both o2 banks are faulty, replaced the o2 sensors, all 4, and the truck ran like crap. The check engine light came back on and it ran great. Reset the computer and again it ran bad until the check engine came back on. Any thoughts?

 

[The_Roadie]

What was the specific code, and do you have a scan tool that can look at the O2 sensor data?

 

[mshoda79]

I don't have a scan tool or know the exact code. The autozone dude checked it out and told me it was two codes, one for each side of the engine. He also tested the o2 sensors after I put them in and it ran bad. I'm getting 16 to 18 mpg with the light on. I can break my tires looses at a 5 to 10 mph roll, so it has plenty of power.

 

[RayVoy]

When an engine is operating at "normal" operating temps, the PCM places the O2 sensors into "closed loop" mode. In this mode, the front O2 sensor(s) relay mixture info to the PCM.

While the engine is "warming up", the PCM ignores the O2 sensors, keeping the system in "open loop" mode. While in this mode, the PCM controls the fuel mix without O2 info.

When the system is in "closed loop" and the driver pushes the right foot (WOT), the PCM drops into "open loop" because the engine requires a richer fuel mix.

When the PCM see conditions, in the O2 circuits, that it does not like, it will switch to "open loop" and set some codes.

Sounds like you are going into "open loop" when you should be in "closed loop".

You have good sensors, but is the wiring to the sensors good?

These sensors have an internal heater to speed up the flip to "closed loop", perhaps one, or more, heater circuits is not working.

 

[gr82bCanadian]

Hopefully last update from me on this topic LOL

Took the truck back to the shop, they scanned for code and came up same MAF sensor again, so they replaced it, we have now went a complete tank of gas and still no SES light YAY!!!!!
So glad this is finally fixed, we have decided to park the TB for the winter and use the Silverado as our Daily drive for the winter, glad to know it will be running tip top for me now with optimum fuel economy