Check Engine Light - Lean Mixture

[mccullionj]

Ok, so i just got a check engine light on yesterday and had it checked at advanced and they said it had three trouble codes all stating "lean mixture". They suggested that it may be a bad 02 sensor.

I just want to know if this seems to be a viable cause and how I determine which sensor is bad. Also, as a side note the truck tends to idle roughly which it has done for some time now.

 

[chevytech03]

not a bad o2 sensor, probley has a intake gskt leaking air past the gskt. were they codes p0171 and p0174? if so, take some chemtool b12 and spray around the intake gkts while at idle, see if it changes.

 

[dye4metal]

im pretty sure there isnt a code that just says "lean mixture" usually they group the numbers of the codes to findout what is i easier

 

[mary900]

Took hubby's '08 Silverado into Dealer today for the P0171 and P0174 codes (the check engine light has been sporadically coming on/off for the past month or so). They replaced the seal around the fuel tank sending unit.

So far so good.

 

[radkon]

Took hubby's '08 Silverado into Dealer today for the P0171 and P0174 codes (the check engine light has been sporadically coming on/off for the past month or so). They replaced the seal around the fuel tank sending unit.

So far so good.

hmm those codes indicate Fuel Trim System Lean Bank 1 and Fuel Trim System Lean Bank 2. Not sure how a seal around the fuel tank sensor would cause those. Since both banks are lean I would think its not an O2 sensor issue either since the odds of both sensors failing at the same time are slim. I'm thinking an intake leak. The codes probably haven't popped up again due to the dealership disconnecting the battery. I'm willing to bet they will appear again shortly.

Ok, so i just got a check engine light on yesterday and had it checked at advanced and they said it had three trouble codes all stating "lean mixture". They suggested that it may be a bad 02 sensor.

I just want to know if this seems to be a viable cause and how I determine which sensor is bad. Also, as a side note the truck tends to idle roughly which it has done for some time now.

Did you get the codes?

 

[chevytech03]

Radkon is correct. After 25+ years working at a GM dealer, i think i might know what codes are what. A seal leak at the fuel tank would set p0442/p0455, evap system small/large leak. I have never seen a seal at the fuel tank sending unit leak unless someone installed it wrong before, also would smell fuel/poss have a leak when full.Are you sure they didnt put in a new pump assy, i have has many bad fuel pumps causing codes p0171 and p0174 due to low fuel pressure on 07 and 08 c/k trucks.

 

[mary900]

Not that I don't trust dealers (but I don't trust dealers) -- but that's why we waited so long to take truck into dealer. We read about the two "lean" codes and we checked everything we could possible check without tearing into something (the truck is still under warranty).

If the check engine light does NOT come back on, it will surprise me. I just wanted to share the info that was written on our service order.

 

[chevytech03]

I can understant not trusting a dealer, there are some that don't know what they are doing, it's a luck of the draw if the tech that works on your vehicle has any experience and is trust worthy. On the other hand, i can't tell you how many vehicles i get that have been to general repair shops and spent hundreds, if not thousands of $$'s on repairs only to have not been fixed, then brought to me, only to find out that it was a minor repair that was an easy fix for me. Some times you get what you paid for. Then there are the ones that go to Auto zone, Oreilly's etc, have codes read and then replace all kinds or parts that weren't needed.Sometimes knowing the product and having inside training specifically of that product goes a long way in doing a proper diagnosis and repair.That is why i decided to get on this forum so i could possibly help those doityourselfers and maybe save them some headaches and money.Not saying i know everything, if I don't i will tell, but if i do, i will hopefully give some help.

 

[vetteluver96]

lean mixture fix

McCullionj,

What was the outcome to the lean mixture, was it your fuel pump or did you have a intake leak?

Cliff

 

[withac]

I am in the middle of getting my Black Bear tune. After looking at my data Justin told me I have an unmetered air leak at idle and I'm close to throwing a lean mix code. He said the likely cause was a leak in the intake manifold gasket, but he also said it could be as easy as a leaky vacuum hose somewhere. YOu'd check that the same way as the intake, spray the vacuum hoses, especially where they connect and see if the idle changes. I haven't been able to find my leak, my mechanic is going to take a look at it tomorrow. Wish me luck, good luck with yours.


So tech03, what happens if I don't fix the leak, what would an unemetered air leak under vaccum do if left unresolved?

Thanks.