DTC P171

[SAUDILTZTAHOE]

I have the check engine light come on on my 08 Tahoe, took it to the dealer and said it was DTC P171 which is System Too Lean (Bank 1)

The dealer said its bad O2 sensor and they are going to replace it, but my question is: if it's a bad O2 sensor the light should be on all the time right? correct me if i am wrong, but the light in my car comes on then it would go off by it self the next day. By the way the car got about 4400 miles on the clock.

 

[emann_01]

if its still under warranty let the dealership do whatever they want ... no money out of your pocket

 

[Black Dog]

Not necessarily, I'm not certain but it could be either in the early stages of going bad, or maybe the system resets each start, and then has to cycle for a while to get an accurate result each session? I have no answer, just trying to provoke thought... What I find interesting is that you were complaining about bad fuel mileage a while back, and now too lean. Coincidence, related, did someone mess with the wrong thing to improve it, or is it just being inefficient? Hmmmm....

 

[SAUDILTZTAHOE]

Not necessarily, I'm not certain but it could be either in the early stages of going bad, or maybe the system resets each start, and then has to cycle for a while to get an accurate result each session? I have no answer, just trying to provoke thought... What I find interesting is that you were complaining about bad fuel mileage a while back, and now too lean. Coincidence, related, did someone mess with the wrong thing to improve it, or is it just being inefficient? Hmmmm....

Thanks for your reply BD and i think that might be the answer to my poor gas mileage. I was reading about the P171 on the net and here's what i found:

P0171 OBD-II Trouble Code
Technical Description
System Too Lean (Bank 1)

What does that mean?
Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.

Symptoms
You will more than likely not notice any driveability problems, although there may be symptoms such as a lack of power, detonation (spark knock), and/or a hesitation/surge on acceleration.

Causes
A code P0171 may mean that one or more of the following has happened:

The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters (K&N, etc.) can cause the MAF to become dirty if the filter is over-oiled
There could be a vacuum leak downstream of the MAF sensor.
Possible Solutions
Possible solutions include:

In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure

I have had noticed all of the symptoms that were noted above from day one but i thought that might be normal duo to our excessive heat, but the detonation (spark knock) i have noticed it two days ago. Should tell the dealer before they start changing parts?

 

[jackyshaikh]

Hi,
I guess there is vacuum leaking problem,check pcv hose which is on left side valve cover end side on that pipe small rubber hose must have torn.that is why there is lean code.

 

[jneal]

i once got this code on another vehicle and it ended up being an intake gasket.

 

[SAUDILTZTAHOE]

The car is going in for service next week or so and will tell them to check for that.

 

[Norris83]

have you had the engine tuned?? I'm just north of you and get hotter temps here... tuned the truck almost 3* more Spark Advance with minimal signs of knock... :/

 

[SAUDILTZTAHOE]

have you had the engine tuned?? I'm just north of you and get hotter temps here... tuned the truck almost 3* more Spark Advance with minimal signs of knock... :/

Nope it's all stock.

 

[SAUDILTZTAHOE]

Well took the car to the dealer on Sun and they replaced the O2 sensors for the driver and passenger side. Today i took it in for 10,000KM service and i went to pick it up, got in the car didn't even move it and guess what? The light was on again, i went back in talked to the advisor and told him about every thing cause the sensors were changed at dealers second branch and they don't know $hit. So the car is going to stay with them for at least 3 days so can figure it out. Stay tuned till i get some more info.

 

[Power_Pusher]

Di you ever get it fixed? If so what was it.

 

[SAUDILTZTAHOE]

Yes it got fixed and the fix was a new fuel pump. Now a put about 5000Miles on it with the new pump and it has been a problem free.

 

[Power_Pusher]

Thanks for your reply

I have both codes P0171 and P0174. I changed the intake manifold gaskets to today and I think it fixed the problem. Prior to replacing the gaskets the Mass Flow Air sensor was reading 3.5 at idle now it is reading 5.2! I will drive it for a few days and see if the codes come back.

Thanks!

 

[SAUDILTZTAHOE]

Good luck.

 

[TJ-Frank]

Thanks for your reply

I have both codes P0171 and P0174. I changed the intake manifold gaskets to today and I think it fixed the problem. Prior to replacing the gaskets the Mass Flow Air sensor was reading 3.5 at idle now it is reading 5.2! I will drive it for a few days and see if the codes come back.

Thanks!

Hi,
have the same and find the problem!
A little hose from the valve-cover at the end of the engine was broken!
I hope you understand me - my english isn´t so good!

 

[brodg]

xTooltipElement
Service Information 2008 Chevrolet Tahoe - 4WD | Avalanche, Escalade, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 2075937
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#08-06-04-016: Diagnostic Information on MIL/SES with DTC P0171 (Fuel Trim System Lean Bank 1) and/or P0174 (Fuel Trim System Lean Bank 2) After Brake Master Cylinder Replacement - (Mar 6, 2008)


Subject: Diagnostic Information on MIL/SES with DTC P0171 (Fuel Trim System Lean Bank 1) and/or P0174 (Fuel Trim System Lean Bank 2) After Brake Master Cylinder Replacement


Models: 2007-2008 Cadillac Escalade, Escalade ESV, Escalade EXT

2005-2007 Chevrolet Silverado Classic

2007-2008 Chevrolet Avalanche, Silverado, Suburban, Tahoe

2005-2007 GMC Sierra Classic

2007-2008 GMC Sierra, Yukon, Yukon XL, Yukon Denali, Yukon Denali XL

with Vacuum Power Brakes (RPOs JD9, JF3, JF7)




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The purpose of this bulletin is to inform dealer technicians to inspect the brake master cylinder seal anytime the brake master cylinder is removed from the vacuum brake booster.





A vehicle may encounter an MIL/SES light set with DTC P0171 (Fuel Trim System Lean Bank 1) and/or P0174 (Fuel Trim System Lean Bank 2) if the seal (1) is damaged or missing. To aid in diagnosis, a technician may monitor the Long Term Fuel Trims with a scan tool. If a lean condition exists, block off the vacuum supply line or hose to the brake booster. If the fuel trims return to normal, the seal may be damaged or missing.

Prior to removing the brake master cylinder, the brake pedal should be applied several times with the engine OFF, until the vacuum is depleted from the brake booster. It is possible that the seal could be sucked into the brake booster if the reserve vacuum is not depleted first. Remove the master cylinder and inspect the seal. Refer to Master Cylinder Replacement (JD9, JF3, JF7) in SI.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

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