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Rear o2 not reseting

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Old Aug 16, 2017, 09:07 AM
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Rear o2 not reseting

Hey everyone,

so I'm trying to get my car inspected, but my rear o2 sensor doesn't want to reset. I drove around 300 miles and did the drive cycle for my old o2 sensor, and still wasn't showing as ready. I bought a new one and installed it, but after driving around for a little bit, it still hasn't reset.. What should I do?
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Old Aug 16, 2017, 09:27 AM
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View youtube video on how an O2 sensor responds behind a good catalytic converter and a failed catalytic converter. Then monitor your rear O2 sensor.
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Old Aug 16, 2017, 09:33 AM
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I also put in a brand new cat*
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Old Aug 22, 2017, 08:11 PM
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Bump! Need help!
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Old Aug 31, 2017, 07:03 PM
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That is weird. It should reset. Did you just buy the car? I just picked up my 2nd evo 9 and have same problem but that is because the previous owner had a wideband set up and cut some wires.


Dealing with that to make things work. If you do not have that problem try resetting it with a scanner. Might work.
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Old Aug 31, 2017, 07:33 PM
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Originally Posted by evo8mrfan View Post
That is weird. It should reset. Did you just buy the car? I just picked up my 2nd evo 9 and have same problem but that is because the previous owner had a wideband set up and cut some wires.


Dealing with that to make things work. If you do not have that problem try resetting it with a scanner. Might work.
I bought the car in April and even when I bought it, the car wasnt inspected.. Now I know why... Lol.. When I bought it, I took it to the mechanics and they said just drive it around... So, I did, and it didn't reset. I then tried doing the drive cycle and it still didn't work.. Then I thought it was the o2 sensor, so I replaced it, drove around, and it still didn't work. So, I did the drive cycle again (with a stop watch for exact time).. Haven't brought it back yet for them to see if it reset.. But I'm guessing it didn't.. Ive driven 2500 miles so far and it hasn't reset.. It's so confusing and annoying.. Can Ecuflash/Evoscan turn it on or reset the sensor?
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Old Sep 2, 2017, 10:51 AM
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See here for the best way to fix this....https://www.evolutionm.net/forums/ec...us-mrfred.html
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Old Sep 8, 2017, 07:14 PM
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Not sure how to do the patch and video is not opening on my end. I am going to get into the wiring this weekend and will take pics. you might want to check it against what you have.


If you have fixed the problem let me know. Interested in your outcome.
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Old Sep 9, 2017, 09:17 AM
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Update! Ok, so I just had the car at the mechanics and they said it that the code didn't reset... After replacing the o2 sensor, driving it for 2200 miles, and doing the drive cycle. So, I guess I gotta buy ecuflash now... What I am thinking is that when the pervious owner had the car tuned, I think he might have deleted the codes to the rear o2 sensor, hence why it isn't resetting. Not sure. What do ya'll think?
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Old Sep 12, 2017, 11:34 AM
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Originally Posted by 4G63_Crazy View Post
Update! Ok, so I just had the car at the mechanics and they said it that the code didn't reset... After replacing the o2 sensor, driving it for 2200 miles, and doing the drive cycle. So, I guess I gotta buy ecuflash now... What I am thinking is that when the pervious owner had the car tuned, I think he might have deleted the codes to the rear o2 sensor, hence why it isn't resetting. Not sure. What do ya'll think?
​​​​​​
I'm no expert, all I ever did was shut off the P0300 code I was constantly having to erase.

The way I understand it, since the car might be sold in many countries and the requirements for emission equipment and monitoring vary from country to country, what Mitsubishi did was write software to operate every possible piece of emission equipment and then made a place in the software where various unneeded tests could be shut off. People that shut off all the tests found the result was pass on all tests at the emissions testing station. As one person put it, "I had equipment pass the car doesn't even have!"

That was about a decade ago, emissions testing people can read forums too. I think nowadays shutting off emissions tests will flunk you in a strict state.
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Old Sep 12, 2017, 11:43 AM
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Originally Posted by barneyb View Post
I'm no expert, all I ever did was shut off the P0300 code I was constantly having to erase.

The way I understand it, since the car might be sold in many countries and the requirements for emission equipment and monitoring vary from country to country, what Mitsubishi did was write software to operate every possible piece of emission equipment and then made a place in the software where various unneeded tests could be shut off. People that shut off all the tests found the result was pass on all tests at the emissions testing station. As one person put it, "I had equipment pass the car doesn't even have!"

That was about a decade ago, emissions testing people can read forums too. I think nowadays shutting off emissions tests will flunk you in a strict state.
The weird thing is that i'm not getting any check engine lights, no codes or anything. So that what makes me believe that the previous owner erased the code, hence why the rear o2 sensor is not resetting... I have no idea, but thats the best conclusion i can come up with.
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Old Sep 20, 2017, 04:51 PM
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So fixed the wiring mess the previous Owner left for me and the sensors are sending a signal which I can read on my scanner tool. However the two items are still not reading ready. Got a lot of feed back on the drive cycles that I am on my way now to do. I did not think the car had anything "reset" and my mechanic friends said that there should not be a way to delete that code but I am thinking they may be wrong. Weird things is that my previous evo was tuned and it did not have this problem so maybe you are right. Let me see what happens with me and will check back with you. Hopefully one get cleared.
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Old Sep 23, 2017, 11:26 AM
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so the drive cycles did not help and did probably what you did. Talked to a few tune shops and taking it there to check if the previous owner disabled the sensor in his tune. I am hoping this visit to the shop does the trick.
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Old Oct 23, 2017, 06:17 PM
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So finally got this fixed...or at least enough to pass emissions. This is what I found out. I took the car to a local tuner and had then look at what the previous Owner had done as far as flashes go. 1. there was a "tune" on the car but it was some ROM/patch they had never seen of before and it really did not do anything as far as performance goes. Odd thing was that all they could see was a very small amount of all the parameters they should be able to.
2. They flashed it back to factory tune and what do you know, my check engine light came back on.
3. At that point I swapped the o2 sensor with a new one. Check engine light turned off right when I did that and doing the drive cycles after that was pretty simple. All I had was o2 sensor (rear) not ready when I went to the emission sensor. I am allowed to have one not be ready so I passed. Checked the other day and now it reads ready so now I am all good.


Hope you got your situation fixed, if not hope this helps.
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