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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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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 ?
Wow, mine is doing that too. I also lose power whenever I accelerate with some determination, then all of the sudden the engine bogs down and loses 80% of it's power. Then I back it off and it seems to go back to the way it was. I noticed it is worse when it is hot, say over 80 degrees, and runs a lot better at that when it is cold out. The coolant usage is quite curious as well. No coolant in the, thank goodness. I saw one video on youtube where a guy found a leak at his flex-pipe, which is part of the cat system.https://youtu.be/jngmRVXCoV4 I haven't got a chance to peak at mine. I also found a guy that found oil in some connectors, however, he didn't bother to identify the parts he was talking about, and I don't know enough to go by what the heck he is pointing at or what he is saying to figure it out.
 

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My 2014 Cruze with 1.4 is running fine but we had a 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 sensor or ??? I am going to replace air filter. I disconnected the battery to check a couple things like 02 harness and now no engine light after reconnecting battery so far, but it’ll probable come back on. Anyone else deal with a 0420 code?
i have had same issues. Ive changed the coil pack and still no help. But i just watched a video about the catalytic converter. He tried to use aftermarket converter and it still wont clear the light and he found that you almost have to use the OEM converter and not skimp on the price. He showed tthesize difference and the standards on how these things work now. The aftermarket ones cant heat up quick enough to keep the engine running right. He is going to update the video as soon as he gets the new OEM part on. I guess i m Going to go ahead and order a new one. Im tired of chamging parts and getting nowhere. Its just hard to believe that the converters dont last longer.
 

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My 2014 Cruze with 1.4 is running fine but we had a 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 sensor or ??? I am going to replace air filter. I disconnected the battery to check a couple things like 02 harness and now no engine light after reconnecting battery so far, but it’ll probable come back on. Anyone else deal with a 0420 code?
i have had same issues. Ive changed the coil pack and still no help. But i just watched a video about the catalytic converter. He tried to use aftermarket converter and it still wont clear the light and he found that you almost have to use the OEM converter and not skimp on the price. He showed tthesize difference and the standards on how these things work now. The aftermarket ones cant heat up quick enough to keep the engine running right. He is going to update the video as soon as he gets the new OEM part on. I guess i m Going to go ahead and order a new one. Im tired of chamging parts and getting nowhere. Its just hard to believe that the converters dont last longer.
Just want to let everyone know. Ive got the light to go away from replacing the turbo. There was a leak in the turbo causing the light to come on. I gor a junk yard turbo for 70 bucks put it on and light is gone hope this helps
 

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Was having a different issue where I'm on the expressway driving about 70 mph when I'd lose acceleration (as though it's not getting gas). I'd pump the pedal a few times and the car would pick up, but blew smoke (bluish white, burning oil). Possible causes mentioned were air leaking from the valve cover, PCV valve or oil cap. Replaced the cap with a new style (GM / Delco, snap in with long neck) before I went to work. By the time I got to work, the check engine line came on with the P420 code. Just now put the original cap back on and will let you know if it goes away.
 

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After putting the original oil cap back on, the check engine light was off the next morning. It stayed off for the next few days, so I reinstalled the new cap as a test to see if the light comes back on. This time, however, the new cap seemed to install much easier (before, it seemed like I had to torque it a bit) and this time I heard a click when it went into place. Been driving a half day and the check engine light has not returned. Guessing I previously had the new cap installed cockeyed and that cause my P420. For those who are interested, here is the old oil cap on the left and the new "standard" oil cap on the right.

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For those of you with P0420 with any combination of other emissions codes, if you have a PCV problem you need to replace the intake manifold, intake manifold AND the PCV hose; dorman 615-380KIT. Right now with code SEPT1 at advanced auto parts it's about 280. The PCV hose contains a rubber check valve that hardens and also gets crudded up with carbon and sticks open not to mention the hose also turns into hard rubber and cracks.
Other items to also purchase are the o-rings on the dipstick, oil cap, and change/check your plugs. The spark plug boots have a nasty habit of hardening and allowing moisture in, corroding the hell out of the springs and resistors, advanced auto also sells boots and resistors for about 40 bucks for the set.

1. The evap and emissions system on this car work very well, however...
2. The fickle PCV system absolutely wreaks havoc on literally everything if you don't fix it quickly. If you pull your dipstick and the engine stumbles significantly you can bet there's an issue.

Additionally, if your PCV issue was severe enough it will eventually damage the front and rear crank seals; the front crank seal contributing to the chirping noise everyone thinks is the serpentine belt or tensioner; the rear will just leak. Third order issues are oil in the boost recirculation valve and leaky cam position actuator seals, and even evap codes (p0442, etc) due to excessive carbon accumulation inside of the evap check valve and solenoid; both of mine were trash and wouldn't hold vacuum.

Now concerning the lean bank and cat performance codes, tech notes also state to replace the coolant temp and O2 sensors together before the cat.

Good luck
 

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Was having a different issue where I'm on the expressway driving about 70 mph when I'd lose acceleration (as though it's not getting gas). I'd pump the pedal a few times and the car would pick up, but blew smoke (bluish white, burning oil). Possible causes mentioned were air leaking from the valve cover, PCV valve or oil cap. Replaced the cap with a new style (GM / Delco, snap in with long neck) before I went to work. By the time I got to work, the check engine line came on with the P420 code. Just now put the original cap back on and will let you know if it goes away.
Just a follow up for those reading this thread that may have something similar. I recently disposed of the car and told the new owner of this issue. He got back to me and said his mechanic replaced the third-party valve cover and PCV valve with an OEM one. That resolved the issue for him.
 
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