P0171 - System To Lean (bank 1 )
Posted 10 March 2009 - 11:49 PM
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Posted 03 May 2009 - 08:32 PM
I bought my 2005 Toyota Corolla a little more then a year ago from the dealership with only 57,000 miles on it. Within about 3 months from the time I bought the car the check engine light came on. I took the car to Autozone to have them pull the code and found out it was p0171 running lean bank 1. The employee for Autozone said it was my o2 sensor in the front of the car on the exhaust manifold. There are 2 o2 sensors on my car (1 on the manifold and 1 on the exhaust itself by the catalytic convertor)he also said it could be the fuel injectors were clogged. He erased the CEL and I decided to go with the cheap possible fix of a fuel injector cleaner called Lucas. Within 3 weeks or so the CEL came back on. I have been told over and over to drive the car with the CEL on and don't worry about it till the car starts running bad but since I worry a lot I decided to get a price on a o2 sensor. For my particular model it's anywhere from $175 to $210. Being the this item is so expensive I decided to keep driving the car the way it was untill I could afford a new one. I told a friend of mine who owns his own shop what was going on and the code p0171. He latter called me to tell me the his mechanics all said that it's not my o2 sensor bit a MAF sensor that's giving that code and that pulling it out and cleaning it would cure the problem. I bought some MAF sensor cleaner and pulled the sensor and cleaned it. I first watched a Youtube video on where it was and how to clean it. One again within 3 to 4 weeks the CEL was on again. I read that if cleaning it didn't do the job then to replace it. The MAF sensor cost $80 so I tried to clean it again first. Within 3 to 4 weeks the CEL came on again. This has got to the point it's driving me crazy! Once again I asked several mechanics and auto part stores what they thought only to get the answer it's my o2 or my MAF. Finally I decided to but a new MAF sensor and pray that took care of the problem. The night before I went to buy one I ran upon this site and noticed one guy who works for Toyota say it was almost always the MAF sensor that caused this code. Another guy put up pictures of what the MAF sensor looks like and what wires to clean. Another guy wrote that cleaning the IAT wires would do nothing and only when I cleaned the sensor wires would it make the CEL from coming back on. I saw the pictures that were on this site of where my sensor wires are on my MAF sensor and realized I've never cleaned those wires and every time I've only cleaned the IAT wires. I pulled the MAF again and have now cleaned those sensor wires and my fingers are crossed again. My thought is that if the CEL doesn't come on within a month or so that I finally fixed it. Remember the MAF sensor is on the air flow box around the air filter housing and has 2 screws in it and a plug. Pull this and clean those wires deep indide it and hopefully you'll solve your problem.
Posted 08 May 2009 - 05:31 PM
This is my first post. I'd like to share with you some of my experiences with the infamous P0171 code.
My 2001 corolla with 70k miles was running beautiflly, but roughly 6 months ago everything started to go downhill.
- First, I noticed was my fuel efficiency, it went from consistent a 37+mpg highway to low 30s.
- Then, I noticed that my engine had a hard time accelerating. When I hit about 2500 rpm, I would hear engine rattle/ping. The noise become so loud that I am afraid to go over 75mph, but as soon as I slow down my car was back to normal.
- The biggest problem started about a month ago, when the engine fails to cold start properly. Instead of starting and shooting up to 2000rpm and settling down to 1500rpm, it starts and immediately drops to 500-800 rpm, making a sound as if it is having trouble turning the crank. It would take a long time before engine get over 1200rpm. Hot start wasn't as big of an issue, but it definitely wasn't right.
- The last straw came when the engine light came on, and boom, the infamous P0171 code.
Here are the steps I took to diagnose my problem.
- First, I tried changing gas stations(ARCO, Valero, Shell, Chevron, 76). I even tried premium gas as part of my experiment. I don't think it was the cause of the problem, but Arco/Valero gas station were definitely giving me some funky noises and *****ty fuel efficiency. This is confirmed with a local mechanic who told me of bad gas station practices, so I'd avoid those Arco/Valero gas stations from now on.
- Second, just to rule out possible problems. I changed my spark plugs to new OEM plugs. The old ones came out to be a bit white(temperature too high), but it wasn't damaged at all. Obviously this didn't fix the problem either.
- Third, I read on many many forums that the air intake path could be a problem. P0171 code further confirmed it. I swapped out my old air filter and cleaned the MAF. Maybe I experienced a 5% improvement, but it definitely wasn't a life changing experience like some of other readers.
- But I kept on looking, and this is when I stumbled acorss this forum. It caught my eyes that some of you guys had improperly cleaned the MAF. Thank you GEORGEINCANADA so much for your posted pictures. I wouldn't have caught these mistakes myself.
After I correctly cleaned my MAF, the first time I stepped on the engine my car JUMPED. I haven't experienced this much power for so long, this is going to require me to change my style of driving(okay, maybe a bit exaggerated). I'm also happy to report that cold start problem is completely gone, and I easily sped up to 80 on the highway without any issues.
As my final words, I'd like to thank everyone for sharing your expertise and experiences. This would have been a $500 job at the dealers, but thanks to all of you I did it for practically nothing and got a huge sense of accomplishment out of it. Hopefully my experiences would help someone else in return.
Keep up the great work gearheads. Good luck on your next projects!
Posted 22 May 2009 - 07:13 PM
P.S. Does my Toyota have a timing chain or a belt, Iím 95% sure itís a chain but the dealer confused me by saying it was a belt?? As I can gather from this site diesels have the belt and petrol have the chain, is this correct?
Posted 12 January 2010 - 10:00 PM
I own a 2001 Toyota Celica GT with about 114,000 miles, and the check engine light came on about 3 months ago. I never took it into the shop because I was still able to drive it and nothing seems to be wrong with it. Then about a month ago, I started to notice my car would shake and appears to want to turn off when I'm idling at the stop light. The RPM would drop and the car shakes then it goes back up. That's when I realize maybe it has something to do with the check engine light. I purchased a hand held code reader and it indicated a P0171 code (fuel too lean). So I went online to see if anyone else have this same experience and found that most people think it's the MAF sensor - mostly needed cleaning. So I checked under the hood for the MAF sensor that is located right after the air filter. Well, what happened next was I guess you can say "by accident". I noticed the air filter cover was not installed properly by the people who last serviced my car - one of the quick oil change places. This Celica has a really tight air filter area, and in the past the service techs don't know how to put cover back properly. (Lately I've been telling them NOT to check my air filter since I can check and change the air filter myself. Well looks like they went ahead and tried to look at the air filter and couldn't spend the time to reinstall it properly.) So I opened it up the cover and while I was in there I changed the air filter. Then I reinstalled the air filter cover securely as it should. Then I turned OFF the check engine light. I didn't do anything with the MAF sensor at this point.
It's been a week now and the check engine light hasn't come back and the car does NOT shake or drop the RPM during a stop light or at idle anymore. I might have been lucky that this problem (P0171 code) was resolved this easily, but I think it's a fast check to make sure your air filter cover is on securely if you have the same issues as my car. Good luck.
Posted 20 January 2010 - 04:32 AM
Posted 21 February 2010 - 05:59 PM
I cleared the error code with my code reader. A couple of days later I get a gas smell, look at the dash and the check engine light is back on.
The car can go into periods of poor acceleration, hesitation, lurching acceleration, seeming like it wants to stall, etc.
Posted 01 March 2010 - 05:33 AM
My truck was doing that too. One thing I discovered is that usually if your system is too lean it's the O2 sensor and something else. The first thing I would check is a leak in a vacuum seal somewhere. You can usually hear it if it's bad enough to trigger the light.
Do you have any other codes too? If you get something about your cylinders / valve clearance and a blinking check engine light I would recommend checking the intake hose. And if you have something about the throttle, I would recommend the PCV, assuming it's spring-loaded. These are some things that could make it too lean if the O2 sensor is broken.
Posted 04 March 2010 - 08:38 PM
Posted 12 March 2010 - 10:56 PM
The code cleared immediately and it has since passed an emissions check.
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