2012 Equinox 2.4L goes in and out of closed loop

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FearlessFreep

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The engine has started going in and out of closed loop. When it goes back into open loop the upstream O2 sensor goes to 0V or really close to it and the engine chugs and runs very rough. Sometimes I can give it throttle and it will go back into closed loop, sometimes it won't. I have already replaced the upstream O2 sensor with a genuine AC-Delco replacement sensor. It has had a P0420 code for a long time so I don't know if the cat iis finally dead or not. Any suggestions on what could be causing this? It has about 182,000 miles on it and it doesn't use oil in between oil changes.
 

FearlessFreep

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I should've also mentioned that when it starts doing this, it's pretty much always at idle, like when stopped at a traffic light or parked in the garage. I can put it in either Park or Neutral and it will run much smoother, or I can apply a bit of throttle and it will smooth out as well.
 

486dx4

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You are not getting any other codes that may be indicating a lean condition - like a P0171? Do you have a scan tool that can look at the long and short term fuel trims to see what they are at idle when this rough idle issue is happening? If you are saying the car runs fine when the engine is not at idle it sounds like something is going lean and causing the rough idle. If the car runs fine when cruising and accelerating, etc then its less likely a fuel delivery problem. The P0420 is as you said low cat converter efficiency and I believe that should not make the car go into open loop. If you can check those fuel trims and the fuel pressure (should really check it just in case) at idle that can go a long way to try to figure out what is happening.
 

FearlessFreep

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You are not getting any other codes that may be indicating a lean condition - like a P0171? Do you have a scan tool that can look at the long and short term fuel trims to see what they are at idle when this rough idle issue is happening? If you are saying the car runs fine when the engine is not at idle it sounds like something is going lean and causing the rough idle. If the car runs fine when cruising and accelerating, etc then its less likely a fuel delivery problem. The P0420 is as you said low cat converter efficiency and I believe that should not make the car go into open loop. If you can check those fuel trims and the fuel pressure (should really check it just in case) at idle that can go a long way to try to figure out what is happening.
Thanks. This ended up being a cracked emissions line that was causing a vacuum leak. I replaced that line and the fuel trims are back where they should be and no more going in and out of closed loop. Fuel pressure seems to be good, don’t think I have any issues there. I do still have the P0420 code though, so I’m guessing the cat is bad. The vehicle has 182k miles and we are not the original owners so I don’t know if it is the original cat or not. It’s pretty rusty so it may be the original cat.
 

swisscheese

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My 2013 has a recall for the after cat O2 sensor which threw a 420 code. Had the recall done. Mine threw a 420 code 2 or 3x after the recall. I cleared the code 2x and after 3rd time it cleared on its own. I would change both O2 sensors before changing the Cat
 

SYDNESB

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The engine has started going in and out of closed loop. When it goes back into open loop the upstream O2 sensor goes to 0V or really close to it and the engine chugs and runs very rough. Sometimes I can give it throttle and it will go back into closed loop, sometimes it won't. I have already replaced the upstream O2 sensor with a genuine AC-Delco replacement sensor. It has had a P0420 code for a long time so I don't know if the cat iis finally dead or not. Any suggestions on what could be causing this? It has about 182,000 miles on it and it doesn't use oil in between oil changes.
Common for it to go into open loop and cut fuel on decel coming to a stop, but should restart. Turn off ECO mode if on. Disconnect both VVT solenoid connectors and see if the idle improves. One or both solenoids may be starting to act up.
 

SYDNESB

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Thanks. This ended up being a cracked emissions line that was causing a vacuum leak. I replaced that line and the fuel trims are back where they should be and no more going in and out of closed loop. Fuel pressure seems to be good, don’t think I have any issues there. I do still have the P0420 code though, so I’m guessing the cat is bad. The vehicle has 182k miles and we are not the original owners so I don’t know if it is the original cat or not. It’s pretty rusty so it may be the original cat.
2012 models that previously had a confirmed oil consumption diagnosis and piston/ring replacement is elligible for a free CAT and O2 sensor replacement. Check with your dealer if the repair was done.
 

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