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2015 GMC Yukon Check Engine Light and Misfires


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I recently changed out my catalytic converter on my 2015 GMC Yukon XL. Originally I had a problem with my check engine light coming on every 6 months or so. After driving it for about 70-100 miles the light would reset and not show up again for 6 months. I had the code run and it would show up as low catalytic efficiency. I recently decided to go ahead and let them change out the catalytic converters (both sides for bank 1 and 2). Once they got to completed I picked it up and the next day the check engine light was on. I took it back to the shop and they said it must be the o2 sensors on bank 2 because the cod was showing low catalytic efficiency on bank 2 only.  They changed out both o2 sensors and I picked the car up again. The next day the check engine light was back on. The code read again for low catalytic efficiency on bank 2. This time they change out the catalytic converter on bank 2 thinking they must have had a faulty part. Once again I picked it up only to have the check engine light come back on. This time it had a new symptom. When I drove it, it had a loss of power, hesitation, rough idle and would misfire (flashing check engine light). After it misfiring one time, it would go back to running some what normal until I shut it off and then it would do the process all over again. I once again took it to the same shop. This time they said they found a pinched gasket and said it must have had a leak. They fixed it and I once again picked it up. The next morning it once again had the same symptoms of loss of power, hesitation, rough idle and misfire. I have taken it back to the shop but they have not found anything yet on why it is doing this. Before all of this I did not have any issue with reliability or run ability with the car. Now I have an issue with the car not performing. I almost wished I would not have changed out the catalytic converter. Does anyone have any ideas that I might could give the mechanics? They said they have already changed at all the o2 sensors. The code they said it always has is P0420 low catalytic efficiency on bank 2. I really need help because the wife is without a car. Thanks 

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On 2/13/2020 at 9:16 PM, Jbc1430 said:

I recently changed out my catalytic converter on my 2015 GMC Yukon XL. Originally I had a problem with my check engine light coming on every 6 months or so. After driving it for about 70-100 miles the light would reset and not show up again for 6 months. I had the code run and it would show up as low catalytic efficiency. I recently decided to go ahead and let them change out the catalytic converters (both sides for bank 1 and 2). Once they got to completed I picked it up and the next day the check engine light was on. I took it back to the shop and they said it must be the o2 sensors on bank 2 because the cod was showing low catalytic efficiency on bank 2 only.  They changed out both o2 sensors and I picked the car up again. The next day the check engine light was back on. The code read again for low catalytic efficiency on bank 2. This time they change out the catalytic converter on bank 2 thinking they must have had a faulty part. Once again I picked it up only to have the check engine light come back on. This time it had a new symptom. When I drove it, it had a loss of power, hesitation, rough idle and would misfire (flashing check engine light). After it misfiring one time, it would go back to running some what normal until I shut it off and then it would do the process all over again. I once again took it to the same shop. This time they said they found a pinched gasket and said it must have had a leak. They fixed it and I once again picked it up. The next morning it once again had the same symptoms of loss of power, hesitation, rough idle and misfire. I have taken it back to the shop but they have not found anything yet on why it is doing this. Before all of this I did not have any issue with reliability or run ability with the car. Now I have an issue with the car not performing. I almost wished I would not have changed out the catalytic converter. Does anyone have any ideas that I might could give the mechanics? They said they have already changed at all the o2 sensors. The code they said it always has is P0420 low catalytic efficiency on bank 2. I really need help because the wife is without a car. Thanks 

This is a tough one,  is this a gm shop? Low cat efficiency with a light coming on every 6 months is not a big deal.  But after everything you have replaced sounds like something else far different  is wrong. Those o2 sensors  may be bad parts if you have rough idle. Also could be an engine misfire which has been known to set of p0420 code.   If you are not at a gm dealer you  may need to bite the bullet and get a 2nd opinion with them.

 

I got this from another site

What Causes This Code?

  • Engine Misfire
  • High Engine Oil or Coolant Consumption (Being burned in the cylinders)
  • Rich or Lean Fuel Mixture
  • Oxygen Sensor

Less Common Causes

  • Retarded Spark Timing
  • Leaded Gasoline Used
  • Leaking Exhaust System
  • Malfunctioning CAT
  • Weak or Poor Spark
  • Coolant Temperature Sensor

 

whats important to note is that  other things could be causing your cat to operate inefficiently other than the cat itself and there was probably nothing wrong with your cat originally as cats usually can last 5 to 10 years they can be used for life of a car but youll just be having some nasty exhaust fumes

 

Edited by Mikey999
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I threw in the towel with the other mechanic shop and took it to the local GMC dealer yesterday afternoon. They had a better system and It was showing several misfires on multiple cylinders on bank 2. They went ahead and kept the car for the weekend since it late afternoon when I brought it to them. They suspect on of the o2 sensors that was put in was possibly bad. Hopefully I will know more on Monday. 

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My GMC dealer was able to resolve the rough idle and misfire issue when they found one of the o2 sensors cross threaded. So far the car performs well without any misfires or rough idles, but still has the code P0430 (low catalytic efficiency on Bank 2) and the check engine light is on. The GMC dealer wants me to take it back to the previous mechanic as they suspect possible leak from the catalytic converter install. They are also calling GM tomorrow for further support. Could the after market catalytic converter not be compatible with my car. The catalytic converter they installed was an AP Emission (AP Exhaust) catalytic converter part #645159. Based off the part number this is the correct cat for the car. I really want to get this check engine light to stay off as the wife is starting to get frustrated. Thanks for any help I can get.

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  • 3 weeks later...
On 2/19/2020 at 9:09 PM, Jbc1430 said:

My GMC dealer was able to resolve the rough idle and misfire issue when they found one of the o2 sensors cross threaded. So far the car performs well without any misfires or rough idles, but still has the code P0430 (low catalytic efficiency on Bank 2) and the check engine light is on. The GMC dealer wants me to take it back to the previous mechanic as they suspect possible leak from the catalytic converter install. They are also calling GM tomorrow for further support. Could the after market catalytic converter not be compatible with my car. The catalytic converter they installed was an AP Emission (AP Exhaust) catalytic converter part #645159. Based off the part number this is the correct cat for the car. I really want to get this check engine light to stay off as the wife is starting to get frustrated. Thanks for any help I can get.

So what happened?

 

Its possible an aftermarket cat can give you issues. Aftermarket parts are not the original and historically always have flaws and compatibility issues. Sometimes  their good for a cheap fix on an older  vehicle where oem may no longer be available or too expensive.

Something like a cat, a major part its likely best stick to oem especially on a newer vehicle. Aftermarket is becoming harder and harder to use as cars are becoming more computerized and calibrated for the original parts. If you go with  an aftermarket bulb you'll probably be ok as long as it does not  report  to a computer in the car.   My tire place once gave me an aftermarket tire pressure sensor on even my older toyota. The light would keep  coming on with false alarms.  Aftermarket plastic bumper cover not a perfect and started  changing color  and fading after a few years. Afternarket bulbs work but maybe burn out quicker.  Thing with aftermarket you have weigh price difference against risk of issues or failure costs and maybe how long you plan to keep the car. 

 

The check engine light has historically been a pain in the ass as when it goes  off your car goes into a low performance mode. Sometimes minor issues cause it usually  emissions related or false alarms.  Then it causes people to start replacing all kinds of parts.

 

In my experience anytime  i had check engine  light go off  it was an oxygen sensor. The light was turned off. It would come back within days. You knew something was wrong. If it takes 6 months to come back on 

 Its probably very minor. 

 

I hope gmc dealer was able to solve your issues.

 

I know  dealers are expensive tend to overcharge. But the newer the vehicle  the more youll need to rely on them. They have all the right equipment to test and relevant experience

 I find you can negotiate with them if they quote you  a price on labor thats high or even parts most  will take 10 to 20% off if you insist and become a regular. I find  they have become competitive on oil changes to get  people in there and away from the lube places

 

Let us know what happened

 

 

 

 

 

 

 

 

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