Just replaced my catalytic converter on my Lj yesterday and today while driving I got a P0171 code. It means bank 1 is sensing too much oxygen. Any ideas?
Help with P0171 code
- Thread starter DropTopDon
- Start date
Your PCM’s trying to compensate for something-
The first thing you need really is a scanner that can read live data
Make sure none of your injectors have rotated and the injectors plug in is getting hot
Make sure you don’t have a significant vacuum leak and that you don’t have an exhaust leak
Listen to your injectors with a stethoscope to see if any of the injectors sound markedly different
Basically the PCM is trying to adjust the fuel mixture and it’s out of its operating parameters triggering the code- It is doing that because either too much air is entering the system or thinks too much air is entering the system- In my case it was the number three injector plug laying on the heat shield-
The first thing you need really is a scanner that can read live data
Make sure none of your injectors have rotated and the injectors plug in is getting hot
Make sure you don’t have a significant vacuum leak and that you don’t have an exhaust leak
Listen to your injectors with a stethoscope to see if any of the injectors sound markedly different
Basically the PCM is trying to adjust the fuel mixture and it’s out of its operating parameters triggering the code- It is doing that because either too much air is entering the system or thinks too much air is entering the system- In my case it was the number three injector plug laying on the heat shield-
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Will look at my injectors. So unless it’s an exhaust leak the new cat install wouldn’t have anything to do with this code? Also if I get my hands on a scan tool which reads live data what would I be looking for?
Go to Harbor freight and get the Zürich that is their most expensive one I think it’s still under $200 and in my opinion if you’ve got a 2005 or later TJ /LJ it will pay for itself
I really think you need to look at that connection and also after you run catalytic converter’s a little bit you need to re-tighten the bolts while it’s good and toasty- The only way the injectors could be causing the problem is if they had a hole.
I worded my question a little wrong. I mean once I have the scanner what settings/numbers should I be looking for to diagnose this?
I’ll give the cat bolts a good tightening next time they are warm.
I daily the jeep so is it okay to continue driving with this code or is it something I need to fix asap? So far I haven’t noticed any performance issues but idle does feel very slightly off.
Well what you’re going to be looking at are your short term fuel trim numbers and seeing if they’re off- STFT - That is your short term fuel trim scanner acronym- It will read that and that number should be somewhere around -2 to 5% ballpark but it’s gonna probably be showing something like 98% -
If you will text me I’ll send you a real good article I’m at 256-990-4394 but I’m going into a meeting in about 10 minutes-
Typically it’s not going to do anything harmful at all- Again make sure there’s no wiring that’s getting too hot I know it’s not likely but mine was going absolutely nuts.
Andy
Here is an article that I read that really helped me understand and gave me some baseline numbers- I know this is not the proper way to give someone a link but it’s the best I know how to do-
My cats came in 2 pieces, the y pipe with the pre cats and then the third cat which connects to muffler. I used a u-bolt exhaust clamp to hold them together. I just put my ear to the clamp where they connect and I can hear a leak. I also feel gusts of air coming out. So looks like I have an exhaust leak.
1. Is it possible that my code is being caused by this exhaust leak
2. Should I have the pipes welded together by an exhaust shop?
1. Is it possible that my code is being caused by this exhaust leak
2. Should I have the pipes welded together by an exhaust shop?
Yes the code is being caused by the leak , the fresh air is mixing with spent air and confusing the pcm via the sensor.
Can you post the fitting pic
I have seen those welded and I believe my 03 is-
Look real close at your pre-cats and makes sure you bolted them evenly
I am leaning toward fresh air in there-
I’m not saying that you don’t have a leak down low but that is way past the downstream sensor-
Everything happens around the pre-cats with 02 sensors-
Look real close at your pre-cats and makes sure you bolted them evenly
I am leaning toward fresh air in there-
I’m not saying that you don’t have a leak down low but that is way past the downstream sensor-
Everything happens around the pre-cats with 02 sensors-
So a leak farther down past the two pre cats wouldn’t cause this code?
I’ll check the pre cat bolts too when I get a chance.
I appreciate all your help!
Not as likely- it isn’t that the cats aren't working , the code indicates you are getting way too much fresh air incoming - and the pcm is adding fuel to balance it (make it richer) and has added so much fuel so long it threw the code (the computer works on percentages)-
Keep in mind the upper sensor and the lower sensor work together to test the air before and after the cat - the lower sensor is not set up to give fuel trim data because the air has passed through the cat - the fuel trim data that tripped the code is coming from the upper sensor- which indicated fresh air is being pulled in above cats-
seems you posted on this yesterday so I will try to find your cat pic-
In my case it was purely an electrical issue , and would code once the wiring got too hot to the #3 injector- basically the injector was shutting down starving it for fuel , but the computer responded based on the fuel trim reading and tried to compensate.
You got this , stay after it
If that were my jeep the first thing I would be doing is getting that upper bank 1 (front) sensor out - Even if it looks good I would replace it-
Your bank one fitment really looks better than your bank two but they’re both close enough that I would not immediately think you’re getting bad air in - unless they are loose -
What I’m thinking is you had a bad bank 1 sensor all along but you couldn’t tell it because of all your cat drama-the computer just could not isolate it til the cats were replaced -
I’m sitting in a 2006 right now- I think what you’re going through is what every owner has to do to live with the 2005/2006 models -At the first sign of failure replace the catalytic converter’s and all the sensors- it is not a defect - it is a wear item like spark plugs.
Also the rich mixture is going to make your mileage drop-
I’m not picking at you -because I’ve done the same thing- Tried to get by with not replacing more than I had to- Basically with doing only 2 oxygen sensors it’s about the equivalent of replacing three out of six spark plugs.
Keep us posted all the way- We need the information to help all of us know how these things are acting and what fixes them.
Your bank one fitment really looks better than your bank two but they’re both close enough that I would not immediately think you’re getting bad air in - unless they are loose -
What I’m thinking is you had a bad bank 1 sensor all along but you couldn’t tell it because of all your cat drama-the computer just could not isolate it til the cats were replaced -
I’m sitting in a 2006 right now- I think what you’re going through is what every owner has to do to live with the 2005/2006 models -At the first sign of failure replace the catalytic converter’s and all the sensors- it is not a defect - it is a wear item like spark plugs.
Also the rich mixture is going to make your mileage drop-
I’m not picking at you -because I’ve done the same thing- Tried to get by with not replacing more than I had to- Basically with doing only 2 oxygen sensors it’s about the equivalent of replacing three out of six spark plugs.
Keep us posted all the way- We need the information to help all of us know how these things are acting and what fixes them.
I also understand not wanting to throw parts at something but really you’re not doing that- you’re doing yourself a favor even if you don’t need them right now- if you’ve had to replace two of your sensors your other two are just waiting to go
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