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    Thread: P0420 Chevy 2010 Aveo Lt

    1. #1
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      Unhappy P0420 Chevy 2010 Aveo Lt

      Hello all, wanted to start this thread to see if anyone had any ideas.
      I have been having the dreaded p0420 code on my 2010 Chevy Aveo. Inspected the Catalytic converter both front and back and they seem to be crystal clean, normal looking (ie, no broken catalyst, and not seemingly clogged with debris or soot.)
      Initially I had p0420 code, then I had P0171. P0138, P0131, P0597,P1133. I took the car to a mechanic and they simply put the car on the obd2 scanner and told me it needed a new catalytic converter, (without checking fore and aft temperatures or testing the O2 sensors) seemed preemptive to simply state that it needed a new CAT with out further investigation, especially considering a new CAT is 1700 and you cannot buy an aftermarket CAT in California.
      I took the car back and replaced the engine thermostat, and then replaced both O2 sensors front and back just to see if this would solve the problem.
      I decided that to replace the converter would bankrupt me because I don't have 1700 dollars to come out of pocket in order to pass smog. And truth be known I could probably only get about 3000 for the car, so I began the long attempt at other methods.
      Mainly washing the catalytic converter out. After some leg work I no longer have any other codes showing up I only have the p0420 code.
      The cat was no longer under warranty, as I have over 130,000 miles on it. I am frustrated because I had a similar issue with a Suzuki aerio before where they replaced the Cat and the computer and still could not get the check engine light to turn off. Then 1400$ later they simply did some trick to force the car to pass smog which it did but then the light came back on a week later.
      The thing that gets me the most about the situation, is the vehicle has never driven so good since I bought it in 2010.
      I've heard that in most later model vehicles the emissions cool off so much there is almost no difference when measuring pre and post temps on the CAT when the vehicle is at idle. I imagine I could do this but one thing I did notice was that the similar theme among all these codes was that there could be a frayed wire or short in the vehicle causing the codes to show up.
      So I did a parasitic draw test because I have noticed a slight delay when starting the car as well. I first used a light. Noticed between the neg battery cable and battery post I have a light that turns on indicating a draw.
      I then put my voltmeter inbetween the neg cable and neg post and notice a 1.5 amp current. Here's where things get weird and least to my understanding. The 1.5 amp draw does diminish over the course of about 5 mins. But when I set up the test again it comes back on then diminishes again.
      I have a very basic Aveo. No power door locks or sunroof, no power windows no onstar. But I do have fuses in place in my fuse box for all of these. The only thing that turns the draw off immediatly is to pull the 50 amp breaker under the hood that feeds the interior of the car. From there I have been unable to determine which fuse is pulling the 1.5.
      At this point I feel like the issue might be electrical, but theres no telling. What a shame if a 2010 Aveo really loses the catalyst after 130000 miles. Either way I still get great gas mileage with the car. Discouraged though. Because Im gonna probably just have to sell it as a mechanics special cause I can't fix the darn thing..
      Thanks ahead of time for any responses. I can create videos pretty easy if anyone wants to see more specifically what I am talking about in terms of the draw. TNX


      Last edited by AVEOLTWIN; 12-15-2016 at 01:57 PM. Reason: Correct spelling and to add more precise descriptions

    2. #2
      LXV-SCOOTADRIVE, ON! 2010AveoLT's Avatar
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      that 1.5 amps is the combined draw of all of the control modules in the car; ECM (Engine control Module), BCM (Body Control Module), TCM (transmission control module if you have an automatic), SDM (Sensing Diagnosic Module, more commonly referred as the Airbag control module) IPC (Instrument Cluster) and the Radio. when the current draw diminishes after the 5 minutes, that is when the various modules are going into their sleep modes, which draws less power. when you reset your test, you are causing all of those modules to wake back up and causing the current draw to go back up to 1.5 amps.

    3. #3
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      The upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. Oxygen sensors are also referred to as O2 sensors.

      Catalytic converters are not normally a "wear" type item, that is they are not designed to wear out and need replacement. If they have failed, it is likely due to something else that caused it to fail.

      A code P0420 may mean that one or more of the following has happened:

      -Leaded fuel was used where unleaded was called for (unlikely)
      -A damaged or failed oxygen / O2 sensor Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
      -The engine coolant temperature sensor is not working properly
      -Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
      -Failed or underperforming catalytic converter (likely)
      -Retarded spark timing
      -The oxygen sensors in front and behind the converter are reporting too similar of readings
      -Leaking fuel injector or high fuel pressure
      -Cylinder misfire
      -Oil contamination

      https://www.obd-codes.com/p0420

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      What's wrong with my car?
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      The parasitic draw for me is a red herring. I just didn't know enough about it. Thank you for the info. Ive been trying a different avenue since.





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