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Discussion Starter · #1 ·
Some back story:
Mother dearest has commandeered my Cruze while we await her appointment with VW regarding the Dieselgate buy-back (she is refusing to put any more miles on her car, which I understand). In her infinite wisdom, she took the cruze to the gas station for a fill up, pulled up at the wrong pump and pumped 3/4 of a tank worth of diesel into my car and drives home. It stalls out about a block and a half from the house and she has it towed to the local mechanic, good guy, we use him often.

Fast forward a week or so, we have the car back after a $550 repair bill. I'm driving to Toronto and my engine light comes on, throws 2 or 3 instances of the P0420 code. Dad tells me to clear it, as it's probably just an after effect of the diesel that went through the system. That was on Monday. Today running around doing errands, the light comes back on with three instances of p0420 again.

What are my options here? Anyone ever had success with solving this issue without a hefty repair bill/ cat. replacement? I've heard of guys solving the issue using seafoam or other cleansing products, and or running a few tanks of premium through the system, thoughts?
 

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Did the mechanic do a full fuel system cleaning, including the injectors? If not you still have residual diesel in there.
 

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I believe P0420 can really only be due to bad O2 sensors, wiring to said sensors, or the catalytic converter getting plugged up - especially if it's the only code. If I remember correctly, P0420 is caused by the computer seeing a data difference between the pre-cat and post-cat oxygen sensors that indicates the cat isn't doing its job. A good mechanic can look at sensor data and stand a good chance of telling you if it's sensor(s) or the cat itself.
 

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Discussion Starter · #4 ·
To my knowledge he did the whole fuel system, dropped the fuel tank out and cleaned it, new plugs, and an oil change. I'll probably drop it back to him tomorrow to get looked at.
 

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I believe P0420 can really only be due to bad O2 sensors, wiring to said sensors, or the catalytic converter getting plugged up - especially if it's the only code. If I remember correctly, P0420 is caused by the computer seeing a data difference between the pre-cat and post-cat oxygen sensors that indicates the cat isn't doing its job.
My manual agrees, but also indicates that problems with the engine not burning cleanly can also cause problems. Things like running rich, running lean, misfire, weak spark, etc. I think the underlying issue is if the engine isn't burning clean enough, then the cat has no reserve capacity to deal with the extra fuel the ECM dumps into the engine to test the cat.

You might want to consult with your mechanic (since there's undoubtedly a "repair warranty"), but my inclination would be to run a cleaner or take other steps to help the engine clean itself out and then see where you're at. Depending on the age of the plugs, you might want to change them on general principle.
 

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Discussion Starter · #7 ·
I will admit that I really have no updates on this issue at this point for a couple reasons, 1) It's not noticeably affecting performance and 2) the car is not up for an E-test until 2019. I will definitely attempt to use a fuel additive and or run some premium through it to see if I can't "clean" the cat some, but realistically I expect that I will be looking to buy something a little newer within the next 12-24 months.
 

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Just curious, are you guys running any aftermarket mid pipes / down pipes? or these problems/codes happening on stock parts....
 

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I had a 2013 Cruze along with 2 other Non-Chevy vehicles that all had the P0420 code over time. Every time the system threw out the P0420 code, I recently fueled up at gas stations that do not have Top Tier Gasoline, so I was not getting the maximum 87 Octane for Regular. I ran the car all the way down to Empty and fueled up with Mid-Grade (89-91 Octane) and within hours of fueling up and driving, the light completely went off and no code was read
 

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Discussion Starter · #12 ·
My car at this point is completely stock. I'm still toying with getting a set of rims for the spring, but given the fact that the car just rolled over 180,000km today and that it's up for an E-test next February, I'll likely trade it in on something a few years newer within the next 12 months anyways, so not much point. Had an issue a few weeks back with a spark plug gone bad (they were all replaced while getting repaired from the diesel incident), but since then it's not throwing any more codes (knock on wood), so maybe it's got another year or two left, maybe not. Do you still get a year "conditional" pass to repair any emissions stuff? If that's still a thing, maybe I'll just drive the snot out of the car through to January 2020 and call it a day. It really doesn't owe me anything as it is now.
 
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