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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?
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A defective cat is unlikely to damage an 02 sensor.
Did you fit an OEM (original equipment) sensor or an aftermarket one? Some cars are fussy about brands.
A bank 1 lean code means just that – the system is running too lean according to the O2 sensor. It could be a bad sensor, or any number of things, including low fuel pressure, clogged injectors, vacuum leak etc. You’d really need a mechanic to analyse the fuel trim data amongst other things to know for sure.
If you’re dead set on replacing the sensor, get a good hydraulic jack and a couple of jack stands – if you have a mechanic friend why not get him to show you how? Otherwise, Eric’s channel has good advice. You’l find removing the sensor easier with an O2 sensor socket – borrow one.
The car relies on feedback from the O2 sensors to regulate the fuel delivery, as well as keep the cat running right, so I recommend you get this sorted.
It sounds like the o2 is telling you that you are lean.
Don’t throw parts at it here. With a scan tool what is
the o2 voltage doing and what is the stft and ltft doing?Yes, I buy the cheapest O2 sensors I could find from the brands APWI or Ultrapower. Maybe that’s the reason? The products never said OE. Should I go for the brand that has OE labeled onto it? Or “OE style” is another option as well. What would happen if I neglect replacing this O2 sensor? I was driving the car with a bad O2 sensor before for about 2 years, I used those same brands at least 4x already.
Well here is the problem. We don’t know that the o2 is the problem.
OE style means it supposed to be like OE. If you keep driving the car
without doing anything You will just keep having issues. We would like
to help you solve the problem but need help from you to do some diagnostic
work to help locate the issue.[quote=”college man” post=118627]Well here is the problem. We don’t know that the o2 is the problem.
OE style means it supposed to be like OE. If you keep driving the car
without doing anything You will just keep having issues. We would like
to help you solve the problem but need help from you to do some diagnostic
work to help locate the issue.[/quote]Indeed. A lean code means the ECU is trying desperately to compensate, so if the o2 is faulty for example your car could be running very rich, meaning poor fuel economy and possibly a shorter life for your expensive cat.
you mean to tell me the machine to check codes can check the O2 voltage and what the stft and ltft is doing? I had no idea. I thought the machine simply reads codes. I usually get my free check engine light at Advance Auto. So what do I do next? Ask for another free checkup or what?
[quote=”college man” post=118614]It sounds like the o2 is telling you that you are lean.
Don’t throw parts at it here. With a scan tool what is
the o2 voltage doing and what is the stft and ltft doing?[/quote]Are you saying ECU is the problem? I’ve looked for parts and it only gave me 2 products: alternator and starter.
[quote=”LandRover” post=118658][quote=”college man” post=118627]Well here is the problem. We don’t know that the o2 is the problem.
OE style means it supposed to be like OE. If you keep driving the car
without doing anything You will just keep having issues. We would like
to help you solve the problem but need help from you to do some diagnostic
work to help locate the issue.[/quote]Indeed. A lean code means the ECU is trying desperately to compensate, so if the o2 is faulty for example your car could be running very rich, meaning poor fuel economy and possibly a shorter life for your expensive cat.[/quote]
No, I’m not saying the ECU is the problem. That would be an expensive thing to replace!
The ECU, or engine computer, tells the fuel injectors how much fuel to put in based on its factory ‘engine map’ and what the o2 sensor is saying about the mixture. If the o2 says the mixture is too lean in the exhaust (it senses too much o2, or oxygen) then the ECU compensates by adding extra fuel to each injector pulse (an increase in short term fuel trim). It can add up to about 20-30% more fuel than the settings stored in its permanent memory. If this change works then the long term fuel trim increases, allowing the short term value to fall back to 0% and oscillate around that zero point (this makes the cat work better)
If the short term and long term fuel trims are maxed out and the mixture is still too lean, you get a code. This should give you some idea of what’s happening to your car but both Eric and ScannerDanner have excellent vids on reading fuel trim data.
As for the scan tool, the more expensive the code reader, the more data you can read with it. Most will tell you what the o2 sensors are saying as the engine runs, as well as the ECU’s fuel trim response. A free check at the local auto parts store will probably not include reading this live data. I’m not sure, as in the UK we don’t seem to have reached the heights of customer service the US has, and I don’t know of any auto parts store that will read your codes, check your battery, or even hire you a ball joint separator for free, at least up here in Scotland.
I see. Usually the bigger reading equipment can read such things. The free readings at auto parts stores they tend to use the small machines. I’ll try to ask if they can use the big ones. What is it that I need to ask them to get a reading on exactly? Also, if the O2 sensor is not the direct problem, what could it be and how do I go on about getting it fixed?
[quote=”LandRover” post=118738]No, I’m not saying the ECU is the problem. That would be an expensive thing to replace!
The ECU, or engine computer, tells the fuel injectors how much fuel to put in based on its factory ‘engine map’ and what the o2 sensor is saying about the mixture. If the o2 says the mixture is too lean in the exhaust (it senses too much o2, or oxygen) then the ECU compensates by adding extra fuel to each injector pulse (an increase in short term fuel trim). It can add up to about 20-30% more fuel than the settings stored in its permanent memory. If this change works then the long term fuel trim increases, allowing the short term value to fall back to 0% and oscillate around that zero point (this makes the cat work better)
If the short term and long term fuel trims are maxed out and the mixture is still too lean, you get a code. This should give you some idea of what’s happening to your car but both Eric and ScannerDanner have excellent vids on reading fuel trim data.
As for the scan tool, the more expensive the code reader, the more data you can read with it. Most will tell you what the o2 sensors are saying as the engine runs, as well as the ECU’s fuel trim response. A free check at the local auto parts store will probably not include reading this live data. I’m not sure, as in the UK we don’t seem to have reached the heights of customer service the US has, and I don’t know of any auto parts store that will read your codes, check your battery, or even hire you a ball joint separator for free, at least up here in Scotland.[/quote]
[quote=”college man” post=118614]It sounds like the o2 is telling you that you are lean.
Don’t throw parts at it here. With a scan tool what is
the o2 voltage doing and what is the stft and ltft doing?[/quote]ok so what I need to do is borrow or buy the big scan tool and read what the O2 voltage is doing? What does stft and ltft stand for? Are you saying if this isn’t an O2 sensor problem it’s something else that the O2 sensor “senses” what the problem is?
[quote=”college man” post=118980][quote=”college man” post=118614]It sounds like the o2 is telling you that you are lean.
Don’t throw parts at it here. With a scan tool what is
the o2 voltage doing and what is the stft and ltft doing?[/quote][/quote][quote=”bananaspree” post=119070]ok so what I need to do is borrow or buy the big scan tool and read what the O2 voltage is doing? What does stft and ltft stand for? Are you saying if this isn’t an O2 sensor problem it’s something else that the O2 sensor “senses” what the problem is?
[quote=”college man” post=118980][quote=”college man” post=118614]It sounds like the o2 is telling you that you are lean.
Don’t throw parts at it here. With a scan tool what is
the o2 voltage doing and what is the stft and ltft doing?[/quote][/quote][/quote]short term fuel trim and long term fuel trim correct if the o2 is switching
right there is another problem.I see. How does one correct the problem then so the code disappears? You’re saying replacing the O2 sensor may not solve the “lean” problem? So in this case, it’s not an O2 sensor problem. What should I expect to replace if not the O2 sensor then?
Hi Bananaspree,
Please don’t take this the wrong way, but if you don’t understand how fuel trims and o2 sensors work then you are unlikely to be able to read live engine data with a scan tool effectively, and will end up wasting your money on the tool and by throwing parts at the car. If you need the car fixed quickly then get a reliable mechanic to examine the car. If you can wait to fix it then by all means watch some ScannerDanner vids on the subject before committing yourself.
Causes of a lean code include: vacuum leak, bad fuel injectors, pump or regulator, bad MAF sensor, bad o2 sensor, bad ECU.
To reiderate don’t throw more parts at it please. Most of the time a lean code is caused by something like a vacuum leak or a loose connection in the intake tubing. Not saying that’s what it is, but it’s worth a check. Or there could be an exhaust leak before the first O2 sensor.
Quick look on identifix suggests you should look at the MAF, for restricted fuel injector(s) or an intake manifold leak.
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