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I had the P0171 and P0174 codes and my mechanic replaced the MAF sensor, car feels much more responsive now.
P0171 is for one bank lean, and P0174 is for the other cylinder bank lean. I wonder if you can assume that if you get both codes, the problem is upstream of the cylinders, like an AFM/MAF or resonator leak, and if its just one of those codes, its something thats on that cylinder head. In my case, the leak was in the PCV valve hose, which is only on the driver side cylinder bank. Any thoughts/experience narrowing it down this way?
I love it when I hear about people solving problems like this for next to nothing when the so called "expert" says it has to be something else.
My GS430 just started throwing codes p0442, p0446 & p0441. They said emmisions and I retighten the gas cap and a week later it came back on so I reset it again and a few days later it is back They said they need to do a smoke test on the emisions system to find the leak. I will troubleshoot myself first....
Update: The dreaded P0171 has not returned. To celebrate, I did lower ball joints, camber arms, tie rod ends. The party continued with new spark plugs, ac air filter, more hoses, and best of all, a serious cleaning, conditioning and re-dye of the leather. Had a new cover made for the console too. They recommended vinyl instead of leather and they did a perfect match and beautiful stitching. Leather Menders in Austin, TX. I highly recommend them if you're in the area and looking for the best. Also did daizen swaybar and rack bushings. Next is struts and then I'm done for a while.
Dont bother with maf or o2 sensors until you've made an exhaustive check for vacuum leaks to fix a P0171.
I still have the cracked pvc hose. If you still want to see a pic, PM me your email and I'll send it to you. I dont have a place to host the pics online.
You dont need a host. You can post "attachments" here on CL if you scroll down below where you're writing your post (in advanced mode) click "manage attachments"
Update: The dreaded P0171 has not returned. To celebrate, I did lower ball joints, camber arms, tie rod ends. The party continued with new spark plugs, ac air filter, more hoses, and best of all, a serious cleaning, conditioning and re-dye of the leather. Had a new cover made for the console too. They recommended vinyl instead of leather and they did a perfect match and beautiful stitching. Leather Menders in Austin, TX. I highly recommend them if you're in the area and looking for the best. Also did daizen swaybar and rack bushings. Next is struts and then I'm done for a while.
Dont bother with maf or o2 sensors until you've made an exhaustive check for vacuum leaks to fix a P0171.
I still have the cracked pvc hose. If you still want to see a pic, PM me your email and I'll send it to you. I dont have a place to host the pics online.
Yes, please send pic, my check engine has gone on and off with this code, hoping it stays off, but...
Update: The dreaded P0171 has not returned. To celebrate, I did lower ball joints, camber arms, tie rod ends. The party continued with new spark plugs, ac air filter, more hoses, and best of all, a serious cleaning, conditioning and re-dye of the leather. Had a new cover made for the console too. They recommended vinyl instead of leather and they did a perfect match and beautiful stitching. Leather Menders in Austin, TX. I highly recommend them if you're in the area and looking for the best. Also did daizen swaybar and rack bushings. Next is struts and then I'm done for a while.
Dont bother with maf or o2 sensors until you've made an exhaustive check for vacuum leaks to fix a P0171.
I still have the cracked pvc hose. If you still want to see a pic, PM me your email and I'll send it to you. I dont have a place to host the pics online.
Thanks for that leather repair. I'm in Austin, I'm going to check it out. Thanks again. I've replaced my evap and air hoses. I'm going to replace the PCV and the grommet. My evap and air hoses are the OG's from1999, so yeah they are hard as a rock and brittle. Hopefully all these new hoses and that new PVC/grommet will fix my leak.
Thanks for that leather repair. I'm in Austin, I'm going to check it out. Thanks again. I've replaced my evap and air hoses. I'm going to replace the PCV and the grommet. My evap and air hoses are the OG's from1999, so yeah they are hard as a rock and brittle. Hopefully all these new hoses and that new PVC/grommet will fix my leak.
I've cruised for 100 miles and the cel light has not come back on (knock on wood).
I changed the pvc hose coming from the air intake box 📦 because the codes p0171 and p0174 kept coming up.
The pvc hose had a big gash which I’m sure was the reason for a vacuum leak resulting in the codes reoccurring.
That will do it. Looks like mine did when I found the leak. Mine was underside of the hose between the cylinder banks. Dealer cracked it (along with other collateral damage) when they replaced the starter. BTW, if you crack a nipple on any of the air boxes, just get a brass plumbing nipple, thread and expoxy it in place. I had to do it years ago and it has never leaked.
I'm new to this thread but have also been dealing with this p0171 code on my 2000 LS400. It's got only 130k miles. I've replaced PCV and hose, all 4 o2 sensors, MAF sensor, ECT sensor, and a used ECU (had it reflashed).
Check engine light stayed off for exactly 399.3 miles (the longest it has ever stayed off) and came back on last night. I'm ready to hang myself.. Any one got any other ideas?
The car has been smoke tested both hot and cold but I'm tempted to check for leaks again.. HELP!
If you ever get stuck with a 0171 code, and you have done all the obvious investigating. Before you spend a dime on hoses or sensors that don’t show any obvious defects. Or in the case of sensors, a corresponding code. Simply locate all your vacuum ports on the intake and block them off. There will usually just be a few of them. I got a few pieces of new hose, and just connected it from one port to another. Eliminating things like the evap system and power steering adjustment entirely. I was able to completely isolate the motor from any possible vacuum leaks. The corresponding systems would kick on their CEL’s as I went. But it left me with only one possible cause of a lean motor. Which would be low fuel pressure. I had been assuming that the obvious symptom of a bad fuel pump, would be failure to start and run. Turns out I was wrong, after I threw a fuel pump in, the code never returned.
I got cel p0171 and it turned out to be oxygen sensor 1 bank 1. Initially i tried to test cacuum leak, replaced MAF sensor, fuel injection cleaning ... etc
.. none of them work. I finally brought my 2007 ls460 to lexus dealer to replace oxygen sensor bank1 and it fixed the problem. My problem was intermittent and it turned out that sometimes O2 sensor is unresponsive ! Just my 2 cents.
If you ever get stuck with a 0171 code, and you have done all the obvious investigating. Before you spend a dime on hoses or sensors that don’t show any obvious defects. Or in the case of sensors, a corresponding code. Simply locate all your vacuum ports on the intake and block them off. There will usually just be a few of them. I got a few pieces of new hose, and just connected it from one port to another. Eliminating things like the evap system and power steering adjustment entirely. I was able to completely isolate the motor from any possible vacuum leaks. The corresponding systems would kick on their CEL’s as I went. But it left me with only one possible cause of a lean motor. Which would be low fuel pressure. I had been assuming that the obvious symptom of a bad fuel pump, would be failure to start and run. Turns out I was wrong, after I threw a fuel pump in, the code never returned.
03-03-10, 11:50 AM
They said they need to do a smoke test on the emisions system to find the leak. I will troubleshoot myself first....
