P0171 code

[Adam]

My car is a 2001 Toyota Celica GT automatic. My buddy installed both O2 sensors first BEFORE changing the catalytic converter so I’m not sure if the defective catalytic converter somehow damaged the O2 sensor.

We just changed the catalytic converter, all codes disappeared, I passed my emission test, but the next day the code P0171 came up. It says bank 1 system too lean. I was informed the front O2 sensor is the problem. Hard to believe considering we just installed it. I’d probably want to try to install a new one on my own. I have never gone down under my car. How do I do this safely? Get a metal support (what’s the name of this?) and a jack, do not remove the tires but simply tilt the car slightly enough so I can get down under it? It’s one thing I’m hesitant in doing is going under my car. My mechanic buddy make it look easy since he has experience.

I already passed my emission test and I’m good for the next 2 years, is it even necessary to fix this P0171 code?

Topic

[Adam]

My MAF is brand new, I would probably use a MAF Cleaner again as well. I think Jiffy Lube checked on my air filter and maybe made it dirty, who knows. O2 sensors are new as well as I have mentioned. I’m still trying to pinpoint what the culprit is here. Catalytic converter is new. The car runs great.

[Andrew]

Why did you replace the MAF sensor? Was there an existing problem?

You’re still trying to pinpoint the culprit because, and I’m sticking my neck out here a little, no-one on this forum can help you make progress until you find out the reason for the lean code. This will involve running the engine with a scan tool connected and analysing the fuel trims, o2 sensors, MAF outout, etc. Sometimes blipping the thottle, forcing a vacuum leak or adding propane to the intake will tell you if the o2s are telling the truth, and help narrow down the suspects.

An ECU does not tell you what the problem is. It’s a dumb machine that sees electrical activity, compares it with reference maps inside, and throws a code if they don’t match. It’s saying to you, ‘I’m not happy with this system – you take it from here’. From the start of this thread you have been saying, ‘here’s the code. What part do I replace?’ and we have responded, ‘X or Y could be happening, but you need to analyse the engine data to know for sure’.

You keep responding with, ‘I see. So what part do I replace?’

To use a cliche, please help us to help you. Get the engine analysed and we can take it from there.

[Adam]

There was an existing MAF problem code. At first I tried to use MAF cleaner but the code came back so I replaced it.

I just went to Advance Auto Parts and asked if they can use the big machine to get a better reading, they said they don’t have the machine nor do they sell it. It’s $10,000 they said. I think that person was exaggerating a bit. Doesn’t these machines cost less than that? I’ll try if Auto Zone would have the big machine. I could probably post an ad on craigslist for someone to check the codes for me with a big machine, maybe for a better price than an auto shop. Most people wouldn’t have this big machine unless they owned the shop.

[Adam]

OK so the check engine light disappeared mysteriously without me doing anything. Not sure what’s up now if that code that popped up was simply a glitch? Not sure if type of gasoline or gas station choice had anything to do with the code disappearing? I used Shell’s V power premium gas.

[Adam]

OK so the code P0171 came back again after about 2 weeks when it disappeared without me doing anything. This time the message is different: misfire fuel comp. catalyst O2 sens. What’s up now?

[Andrew]

Just to clarify, do you have two codes now, or the same P0171 with a different message? If the latter, that sounds very odd.

[Kenneth]

[quote=”bananaspree” post=119356]There was an existing MAF problem code. At first I tried to use MAF cleaner but the code came back so I replaced it.

I just went to Advance Auto Parts and asked if they can use the big machine to get a better reading, they said they don’t have the machine nor do they sell it. It’s $10,000 they said. I think that person was exaggerating a bit. Doesn’t these machines cost less than that? I’ll try if Auto Zone would have the big machine. I could probably post an ad on craigslist for someone to check the codes for me with a big machine, maybe for a better price than an auto shop. Most people wouldn’t have this big machine unless they owned the shop.[/quote]

You don’t need the expensive, shop type scanner. All you need is a scanner that reads live data. That’s all you need to look for, in a scanner.
I bought mine at harbor freight for around ninety bucks, and it also reads ABS codes. It’s made by a company that makes some pretty decent scanners. Although the same unit that says Autel on it goes for slightly less than three hundred. It’s worth a look.

[Tri9SS]

I would see if the freeze frame data tells you when the code was set. If it was set at idle then I will look for a vacuum leak first. if it was set underload like say traveling at 30 MPH then I would check fuel pressure because something is causing you to get the lean condition under load, like low fuel pressure, cloged fuel filter, bad fuel pressure regulator, bad fuel injector, ETC.

[David]

I believe this is what was referred http://www.harborfreight.com/can-obd-ii-scan-tool-with-abs-60796.html

Hmmm, may have to get one myself. ABS and manufacture specific codes, yes please.

Anyways, Advance sells an Actron scanner than will display fuel trim info, RPM, and other various stuff, it runs $250 I think. Sometimes the stores will use that one, other times its the $50 one. Just various from store to store, I should know, I worked for Advance.

But that guy didn’t know what he was talking about, you don’t need a $10k scanner just to read a few things like O2 sensor voltage and fuel trim. Heck, he may be even using a scanner capable of doing so and not realizing it.

[Adam]

I think I have 2 different messages from the one code P0171. The lady that checked my engine light code said something about it. She was using a small scanning tool. She went back inside the Advance Auto store to get the bigger scanner but I think the manager may have said something to her. They probably do not like going through all the hassle of doing free work, so why offer it? LOL.

[quote=”LandRover” post=121181]Just to clarify, do you have two codes now, or the same P0171 with a different message? If the latter, that sounds very odd.[/quote]

[Adam]

The code came back while I was driving. I don’t remember if it was at highway speeds or not, if that matters.

I think I may have been traveling at heavy traffic so at about 30mph.

When I had a new fuel pump installed, the guy who installed it said my car didn’t come with a fuel filter and or it doesn’t need one. It was either on the fuel pump already, but I had asked him about a filter. I was able to buy a fuel filter at Rock Auto though. I’d have to look at the fuel pump if in fact it’s missing a fuel filter so I can install one.

I remember a time when I had been driving my car for years and decided to replace my cabin air filter and to my surprise there was no cabin air filter installed so I was breathing all those bad air all those years. If someone has a video on how to change my fuel filter let me know. Maybe it’s time to do it myself and check. It’s a pain in the ass considering it’s under the backseat.

[quote=”Tri9SS” post=121394]I would see if the freeze frame data tells you when the code was set. If it was set at idle then I will look for a vacuum leak first. if it was set underload like say traveling at 30 MPH then I would check fuel pressure because something is causing you to get the lean condition under load, like low fuel pressure, cloged fuel filter, bad fuel pressure regulator, bad fuel injector, ETC.[/quote]

[Adam]

as I mentioned before (on page 2 at the bottom of the thread), the code vanished for 2 weeks and came back on driving at 30mph. It has disappeared again driving at 50mph. My observation first was when it disappeared I had used Shell gas station using V-Power premium gasoline. When the code came back on, I had used a Hess gas station’s premium gasoline. Now, my code vanished again when I filled up my tank using Shell gas station’s V-Power premium gasoline. It took about 2 days after I had filled up my tank for the code to disappear. I’m only assuming the type of gasoline/gas brand may have something to do with the code coming on and off? What could this be telling me then? All I know is that the car seem to like Shell but it’s odd something like a gasoline would make check engine light codes pop up. Something in my car is rather “weak” which is probably why it’s picky with what type of gasoline or gas brand it uses?

[Author]

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