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2000 Toyota Corolla PO125 and P0171


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MCheshier1
Novice

Jul 12, 2015, 1:42 PM

Post #1 of 11 (1564 views)
2000 Toyota Corolla PO125 and P0171 Sign In

I was reading through some of your posts about the P0125 code and thought maybe you could help as I have had 5 dif mechanics unable to fix the problem. I have a 2000 Toyota Corolla and it's getting the PO125 code and also P0171. We replaced the upstream 02 sensor and the light stayed off about 3000 miles, but it's back on again and getting terrible gas mileage in the city. Not so bad on the highway. Do you have any ideas about these two codes?


Hammer Time
Ultimate Carjunky / Moderator
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Jul 12, 2015, 1:54 PM

Post #2 of 11 (1561 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

Both of those codes are indicating a lean condition. The overall most common cause of that is a vacuum leak although there are numerous other things possible. Another common cause is a tear or hole in the intake snorkel between the MAF and the throttle body. A smoke test would be recommended to look for any vacuum leaks.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



MCheshier1
Novice

Jul 12, 2015, 4:45 PM

Post #3 of 11 (1551 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

Ok, I had to contact the guy who worked on it first and he said the first thing he checked was for vacuum leaks. I did a second inspection and every hose, clamp, etc. in that area including the one from the MAF is in perfect condition. No visible damage and not one crack. That guy change out some cooling thermostat and then suggested he go through my fuel system and that's where I told him to stop bc I already spent too much on trial and error. Another guy just told me to change out my MAF.


Hammer Time
Ultimate Carjunky / Moderator
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Jul 12, 2015, 4:49 PM

Post #4 of 11 (1549 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

The MAF is a possibility but not that common. I wouldn't disregard the vacuum leaks until a smoke test has been done. Other methods are not that reliable.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



MCheshier1
Novice

Jul 12, 2015, 4:55 PM

Post #5 of 11 (1547 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

Does it matter that it's not running badly? He said that he did the vacuum test at his shop, that and that the car isn't running roughly indicated to him there wasn't a leak. The biggest problem I am noticing is the horrible gas mileage. But if you think I should get someone else to run the smoke test, that's the next step I guess.


Hammer Time
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Jul 12, 2015, 4:58 PM

Post #6 of 11 (1545 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

yes, I do. That guy doesn't know what he is talking about. The computer has the ability to adapt to lean conditions to maintain a constant 14.7:1 air/fuel ratio so the vehicle will still run normal. The code is only set when the computer has reached it's adaptive limits so yes, you can have a leak and it will still run good.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Jul 12, 2015, 5:04 PM

Post #7 of 11 (1541 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

Need to look at freeze frame capture data for the P0171 to see what was going on when the code set. It also would be helpful to monitor fuel trim data and different engine loads to see if you should focus on vacuum leaks or fueling issues.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 12, 2015, 6:06 PM)


MCheshier1
Novice

Jul 16, 2015, 2:50 PM

Post #8 of 11 (1486 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

I have an update on the codes. I thought the 171 was still there but hadn't actually checked it again since it had come on in the past. The codes I am now getting are P0125, P0130 and P0133.


Discretesignals
Ultimate Carjunky / Moderator
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Jul 16, 2015, 4:27 PM

Post #9 of 11 (1481 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

What brand and part number O2 sensor did you install? Don't use Bosch in a Toyota cause you will end up with problems. Denso or NTK is preferred.

We need datastream information to see what is going on with the fuel trims and O2 voltages. Without testing and looking at scan tool data can't really give you any advice. Surprised five mechanics have not been able to figure this out.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 16, 2015, 4:27 PM)


MCheshier1
Novice

Jul 16, 2015, 4:34 PM

Post #10 of 11 (1478 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

It's a Denso. I usually replace my parts with whatever is already in there just to be safe. The light was off for about 3000 miles, then came back on. I didn't bother to check the codes then because I assumed they were the same. However, two auto techs since then have looked at it. I have a scanner, when it cools off I will go out there and run the freeze frame data and figure out how to copy and paste it if I can. Thanks for your help : )


Discretesignals
Ultimate Carjunky / Moderator
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Jul 16, 2015, 4:47 PM

Post #11 of 11 (1476 views)
Re: 2000 Toyota Corolla PO125 and P0171 Sign In

Freeze frame data will tell you what was going on when the code set. It is helpful in duplicating a concern to figure out what is going wrong. The problem is you also need to view live data, so you can analyze what exactly is going on with how the O2 sensor is outputting and how the computer is reacting with fuel trims. Seeing one frame of data really isn't going to help.

For some reason the O2 sensor has a circuit issue and a slow response problem. The sensor needs to be tested by watching when happens to the O2 voltage when you induce rich and lean conditions. It also needs to be monitored while your driving and putting the engine under different loads. Monitoring the rear O2 sensor helps is see if the front sensor is responding properly. Of course, sometimes these problems can be intermittent or temp related. To diagnose this you really have to understand how the O2 sensor functions and how the computer uses this information to control the fuel to air mixture, so the catalyst is operating in the right environment. This is not something you can learn overnight and be proficient at.

Do a good visual of the sensor, its harness, and connector. Make sure the harness or connector hasn't found itself melting on the exhaust or chaffing on something. Be sure there is no oil leaking onto the connector, harness, or sensor. O2 sensors can be poisoned by coolant, oil, and/or silicone. If the engine is burning lots of oil, it will eventually take out the sensor.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 16, 2015, 4:59 PM)






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