the P0171 code, lean fuel mixture

[JimP]

I get this code randomly now. I clear it and it goes away for a week or so but comes back. Seems coincident with a cold start.
I borrowed my friends scanner which exposed PO171 lean fuel mixture. Long term mixture advises limits of +/- 25%. I think this implies a ratio. My engine reads 14% idling. If I step on the gas it drops to around 0%.
The question I have is what is in the denominator vs the numerator. Is it fuel/air or air/fuel?
Considering the percentage drops when I rev the engine and (give it more gas) I would assume it is air/fuel. Apparently the amount of gas equals the amount of air when stomping on the accelerator pedal. Lotso air and little fuel at idle means it's lean and is illustrated by a bigger percentage.
Am I thinking about this correctly and is 14% on the high side?
I think I should be checking for air leaks at the intake and fuel pressure overall.
BTW a service guy changed the fuel filter because he observed it was leaking about two months ago back when I didn't have the problem ironically.

 

[02LTD2.0]

Yep....probably some vacuum leaks.

 

[silverbullet04]

Also check your orange rubber seal on your map sensor, they tend to break apart and can cause a vacuum leak. Here is mine before I replaced the rubber seal.

 

[JimP]

Interesting - yesterday I put the scanner back on. Now the long term and short term fuel air mixture reads 4% and under.
In the words of John Cleese from Monty Python after telling his fellows during the parody of the Salem witch hunt "She turned me into a Newt......I got better".
It may be intermittent so I will be keeping an eye on it.
There are no misfires BTW.
I did notice some chewed injector wires. Inches of bare copper were exposed but intac. I retaped them. The car sat for quite a while before I purchased it. I found quite the rodent nest under the engine cover in that area which I blew out before leaving the sellers place. There was a curious gray squirrel in an oak tree in front of the seller's garage. We found many acorns shells around the engine.
I noticed many of the wire bundles appear to be brittle in general though.
Know of any liquid treatment I can apply that might extend the life?

 

[JimP]

Problems that go away mysteriously come back mysteriously". said Confucius.
It's definitely coincident with the ambient temperature being low, real low, like less than 10degF.
I'll get the code immediately on startup on a cold day. Watching the scanner long term fuel mixture in real time reveals the mixture reads high, 14%, which is approaching the 25% limit. If I run the car for 15mins the value begins to come down into the correct territory of 0%.
This make me think that the Heated Oxygen sensor is not being heated. Fuse 20 is good. Perhaps it's an open wire.
I have perused my Buick Service Manual, and for the life of me cannot find the schematic for the Heated Oxygen Sensors.
Are there a pair of wires dedicated to the heating element or does the heating element share a ground return with the sensor element?
If anyone has a diagram kindly post it in response here.

 

[DrivenDaily]

Wiring diagrams at this link:

Thread '2000-2005 Buick Lesabre Wiring Diagrams'

Nov 18, 2023

If you need A wiring diagram for your 2000-2005 Lesabre I have more than likely every diagram you could need for it found a site for 15 bucks that seems like it covers everything on that car you can message me with a email and I can send the entire catalog to you in zip file or I will leave the link I got them from and you can get them that way up you but figured no since in everyone having to buy them when I already paid for them and can send a copy to you here is link if it pops up black screen saying verifying your connection just wait till it give you the check box it and it will take...

• BossHog39

• 

 

[JimP]

Thanks Drive, Daily,
I have to say I'm disappointed with the "Buick Lesabre Service and Repair Manual I bought on line as a PDF for $30.00.
There's no index!
I spent the morning scrolling through all 4750 pages. I gave up on page 3000.

 

[BuickGirlFromMars]

2004 lesabre HO2S diagram, not factory diagram but its color coded and its 1 of 4 diagrams that pan left-to-right and its the 4th one so this is the right most of a large wide diagram