Code p171 issue

KAISER23

MEMBER
2005 BUICK CENTURY
3.1L
6 CYL
2WD
AUTOMATIC
120,000 MILES

I am getting the the p171 code. Fuel mixture too lean. So far I have replaced the mass air flow sensor, fuel regulator and the upstream oxygen sensor. The light stayed off for about 150 miles then came back on. I started to look for a vacuum leak. I noticed that their is a hose that is below the fuel pressure regulator that isn't connected to anything. Did I maybe disconnect this when putting in the regulator? Before I remove parts I may be asking a dumb question but would there be any reason why that hose is not connected to anything? Thanks in advance. Also, is there anything else that you would have me check? I have the downstream oxygen sensor as well but haven't had time to put it in. I tried the other night but it was very stubborn and I had to work the next day. Also will be changing out the fuel filter this week.

2 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good afternoon,

Can you check the actual fuel pressure? That is the most common issue for the 171.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Do you have a scan tool to check the long term trim?

Also, check the PCV valve.

Roy

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Sunday, April 14th, 2019 AT 1:47 PM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

That is not a dumb question. I know no such thing. And the answer is no. If there is a hose there, it was made to go to something. And if it is a vacuum hose, which I am 99.9% sure it is, then, more than likely, you've found your problem. In the diagrams below I have included the Vacuum Hose Diagrams for your vehicle. The first is for the Emissions Systems and the second is for the Evaporative System of your vehicle.
Please use the diagrams and get the hose attaches. Erase the Direct Trouble Code with a code reader and get back to us with what you are able to find out, please.

Thanks,
Alex
2CarPros

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