Trouble code P0171

It sounds like the fuel pump is weak but to be sure this guide will help us fix it


https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers


Please run down this guide and report back.

Hi, I recently took my truck to get a smog check an it failed. The code came up PO171. It's running to lean. How can I fix this problem. The guy at the check smog told me that he can fix it for 400 to 500 dollars. He doesn't even gurantee me that the truck will pass check smog. It sound like this guy is trying to cheat me out of money. I'm not sure what to do.
I have a friend that fix Toyota cars and he said that: it usually is the master air flow sensor on the intake. I haven't change that but I really need a professional answer. Please help.

Thank you

Roger C.

Hi there, the mass air flow sensor can cause this code but so can vacuum leaks and exhaust leaks up stream of the 02 sensor, i would be checking these first.

Mark (mhpautos)

Freeze frame. .....
Cal load 10.1%
STFT 5.4%
LTFT 34.3%
Rpm 905
Ect 194f
IAT 89f

I replace bank1 o2senor
New spark plug
Check voltage and ohm on mass air flow.... Good in range
Check for intake, vaccum leak
Replace fuel filter
..... I don't have have tool to check fuel pressure, my guest the problem might be fuel pressure regulator but I want to see what you think it might be just by looking at the freeze fame,

o2 is not the issue. 34% long term is the issue.

you have a vacuum leak somewhere.

the causes could be vacuum leak, pcv valve, mass air flow sensor or low fuel pressure. one of these will the cause. after you repair it, clear the memory so it starts the long term count over again.

Roy

My 4runner 2000 used to have p171 code at ~90k in 2008 ago and I found the fix online but my technician do not listen to me in the beginning. After he failed to fix it for two times, instead he replaced O2 sensor according to the repair manual. Every time he reset the memory, the check engine will come back after 50-100 miles. The fix on the third time was simply by removing mass air filter MAF sensor and we found a thin hair short cross the two metal wire inside of it. Clean it by a blowing airgun and put it back. Now it has 137k on it without further problem. Be careful when removing MAF filter because two screws are easy to be damaged and we actually drill one off- this was also pin pointed by that original post maybe from yoto-tech BBS.

I just solve the problem, .... Problem was the vacum line from fuel pressure Reg, I pull out the vacuum line from the fuel pressure regulator and find out that the line was sucking so much air, so I check on vacuum diagram and found it was the line was route it wrong