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Code P0420 Causes

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My 2014 Cruze with 1.4 is running fine but we had an engine light and there’s a P0420 code. Hesitate to mess with plugs given the trouble people have with plug boots tearing.

Is there a way to figure out if it’s the plugs, 02 sensors, or ??? I am going to replace the air filter. I disconnected the battery to check a couple of things like the 02 harness and now no engine light after reconnecting the battery so far, but it’ll probably come back on.

Does anyone else deal with a 0420 code?
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Just another update... I have had the code steadily since my last update here at 110k miles. Now I am at 125k miles and it went away again.

There was a deal on "3M complete fuel system cleaner" and I have never put anything in my tank since I bought it brand new so I figured it couldn't hurt anything to run something in there so I got it. Its normally really expensive but apparently worth it since my CEL went away after running it for 3/4 of a tank. No other changes besides running this in my gas tank, I filled up at the same gas station as I always do with the same grade of fuel and same commute and everything.

I'll update this thread again if or when the light comes back on.
I use the Chevron with techron stuff or seafoam in the gas tank. Haven't had any issues or that specific check engine light... this car is actually quite weird as I had boost/vacuum leaks with the intake manifold gasket, throttle body gasket and valve cover gasket and had surges at idle but never a check engine light on this dang car.
 

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Just another update... I have had the code steadily since my last update here at 110k miles. Now I am at 125k miles and it went away again.

There was a deal on "3M complete fuel system cleaner" and I have never put anything in my tank since I bought it brand new so I figured it couldn't hurt anything to run something in there so I got it. Its normally really expensive but apparently worth it since my CEL went away after running it for 3/4 of a tank. No other changes besides running this in my gas tank, I filled up at the same gas station as I always do with the same grade of fuel and same commute and everything.

I'll update this thread again if or when the light comes back on.
Hi, Rich. i have the same code and 2 extra codes: P0171 & P013A. So i'd like to know if the last action worked. the mechanic saidme it could be the fuel pump but I don't know how true it could be (based on the readings he saw on the scanner).
regards
 

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Looks like the last time I posted something was back in May. After the refurbished catalytic convertor didn't work, the auto shop looked around to see if they could find a solution. The only they found was to replace the convertor with a GM convertor. I said to go ahead and found out it was on back order so I had to wait a few weeks. Came into the shop right before the GM strike and they put it on. That was back in September, and I'm happy to say the light has not come back on (though I hold my breath every time I start the car and was afraid to post here in case it jinxs it).

I think this is a problem GM caused and only they know how to fix it.
 

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Just another update... I have had the code steadily since my last update here at 110k miles. Now I am at 125k miles and it went away again.

There was a deal on "3M complete fuel system cleaner" and I have never put anything in my tank since I bought it brand new so I figured it couldn't hurt anything to run something in there so I got it. Its normally really expensive but apparently worth it since my CEL went away after running it for 3/4 of a tank. No other changes besides running this in my gas tank, I filled up at the same gas station as I always do with the same grade of fuel and same commute and everything.

I'll update this thread again if or when the light comes back on.
WOW "3M complete fuel system cleaner" ! Did it work for a long time? I still have my engine light on... LOL
 

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So here is a weird one.............my CEL has been on for over a year now, with P0420 being the main code that would not go away (other codes, like 'random misfire', were cleared with new plugs and coil pack). I live in Taxifornia, and they want a ludicrous sum of money for a 'CARB approved' catalytic convertor ($1300 !!!! vs about $300 in the other 49 states), so that's why I have been living with the CEL being on. Anyhow, my 2014 Cruze 1.4 ECO started consuming coolant the last few months, with no obvious leakage observed on the ground under the car, and only the rare occasional odor. I finally got tired of topping off the coolant reservoir bottle 3 times a week, so I had my (trusted) mechanic take a look; he installed a new radiator, upper and lower hoses, thermostat housing, and coolant overflow bottle hose. Lo and behold, the CEL was not only off after the repair, but so far it is STAYING off. I am scratching my head trying to understand how a coolant system issue could throw up a P0420 code. Thoughts ?
 

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Hey guys. Experiencing same issue. P0420. I've replaced the O2 sensors, catalytic, the plugs, and the coil. I've spent almost $2,000. and the code keeps coming back between 1 day and a month after every repair. I'm at a loss, I don't know what else it could be.
 

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Hi guys same issue, but a sonic. Do all the recommended replacements up to 100,000 miles plus a new cat at 95,000 and timing belt at roughly 105,000. Major issues decided to get a case # with GM no help like the do not care. Almost as if designed to have major head aches to make you dump it to purchase new????? Mechanic did most CEL light work used mostly GM Parts with consistent CEL light issues after and says running fine ignore the p0420 code, but if another code comes up let him know. Really disappointed 95,000 mile star, and p0420 problems for a little over 10,000 miles major ??????'s
 

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Hello please help, I have a 2013 Chevy Cruz 4 cylinder turbo, I have replaced the catalytic converter 2 months later the light came back on with the same code, i brought it to the shop and they said the converter looked fine not sure what they did to test it but then they said to replace the o2 oxygen sensors, so I did, 3 days later light came back on, then went back they cleared history, 5 days later the code comes on again, the car still feels sluggish?! can the shop test the parts to make sure they are working i did not have the shop fix it, it was too expensive but i took there suggestions and bought the parts and had someone put them in?! the light stays on until i bring it to shop they clear it 5 days later the light comes back on
 

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Hello please help, I have a 2013 Chevy Cruz 4 cylinder turbo, I have replaced the catalytic converter 2 months later the light came back on with the same code, i brought it to the shop and they said the converter looked fine not sure what they did to test it but then they said to replace the o2 oxygen sensors, so I did, 3 days later light came back on, then went back they cleared history, 5 days later the code comes on again, the car still feels sluggish?! can the shop test the parts to make sure they are working i did not have the shop fix it, it was too expensive but i took there suggestions and bought the parts and had someone put them in?! the light stays on until i bring it to shop they clear it 5 days later the light comes back on
Hello I too am experiencing the 420 code after replacing converter and O2 sensors. I have found tho that the PCV valves in the air intake manifold can go bad as well as the diaphragm on the valve cover causing this code to appear. I am going to replace them and will leave an update but I would have those checked as they are a common failure on this vehicle
 

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Check the pcv valves and the valve cover
Has anyone else had this fix work? I had a warranty repair on my PCV Valve cover @ ~60k. Just wondering because every single person on here seems to have found a different way to fix this **** code and I REEEALY dont have 2-3k to throw at the wall and see what sticks.

What did you have to have replaced? The valves ot the cover?

(Ps 2015 1.4 Turbo ~115k been fighting with code since 2019. Would come on once a year and I would clear it to see if it came back on (only when over 90° outside) but has come on twice this year. Replacing the upstream O2 sensor kept it off for like 4ish weeks. Mine is specifically p0420 (bank 1) if that matters)

Thanks!
 

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I found a technical service bulletin that stated if the 0420 code appears to check the intake manifold pcv and valve cover before changing the converters. If you google it I’m sure it will come up. Like you said I threw 2 grand at mechanics saying fix this and fix that and none of it worked. But if you YouTube it will show how to check the air intake manifold and valve cover because they are notoriously known for failing together. When this happens the fuel and air ratio is thrown off which will cause the car too run lean or rich and make it think that there is something wrong with the converters triggering the code. I just received and installed mines a few days ago tho. So far so good but if anything changes I will update
 

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O and when u had the valve cover fixed they should have checked the manifold so I would double check if they did because as I stated both are known to fail together on this vehicle and when you order one part it even comes with a recommendation that both are inspected
 

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I've had my CEL going on/off with P0420 for the last 6 months or so. With the current state of affairs, I've been working from home so most of my driving has been within 10 miles of home. Last time I went in to get a code reader to see if anything new had popped up, the counterperson suggested that I take a few longish (30 minutes or more) drives to get the car fully warmed up. I went ahead and drove across town a couple of times, and after that the CEL cleared itself again. Not that it's the only issue that can cause that code to trip, but I'll keep it in mind when it happens again.
 

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So I replaced the spark plugs last and it turned itself off shortly after replacing the spark plugs and it went away for about 7k miles and now its back again. That is the longest it has gone away since it started throwing that code. So I'm inclined to replace the coils next? I'll be shopping around for a better setup though, I have already had problems with the coil which was covered under warranty but now that its over 100k I'll be looking for an aftermarket upgrade. Either way I'll post updates here if I find a cure or not.
I know it's been a very long time so your issue may have been solved, but I wanted to add my experience in case it can help someone else....
it is apparently quite common for the spark plugs to become loose in the Cruze!! for me it manifested in a chirping noise that was almost like a squeak or a beep, speeds up when you hit the gas. it is the reason my car gave the P0420 code
I figured it out after watching several videos of the same sound on YouTube, the chirp was gone once we tightened the plugs and the code hasn't come back yet! crossing my fingers
 

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Any resolution for this? Mine is a 2015 Cruz Same mileage same issue?
Welcome aboard!(y)

Are you trying to ask someone in particular about this?

Don't forget to introduce yourself and your Cruze here.
 

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I know it's been a very long time so your issue may have been solved, but I wanted to add my experience in case it can help someone else....
it is apparently quite common for the spark plugs to become loose in the Cruze!! for me it manifested in a chirping noise that was almost like a squeak or a beep, speeds up when you hit the gas. it is the reason my car gave the P0420 code
I figured it out after watching several videos of the same sound on YouTube, the chirp was gone once we tightened the plugs and the code hasn't come back yet! crossing my fingers
Welcome aboard!(y)

Yes it is/was very common.

Don't forget to introduce yourself and your Cruze here.
 
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