# Check Engine light- P0420 code



## diesel (Jun 8, 2013)

I am pretty sure there's another thread with that same code. It wasn't me though.


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## fj40intow (Nov 4, 2013)

diesel said:


> I am pretty sure there's another thread with that same code. It wasn't me though.


I tired to search for a thread before posting.


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## fj40intow (Nov 4, 2013)

I took the car to dealership for them to look at it.
They wanted to keep it as they said they may have to call GM.
They gave me an Equinoix as a loaner.

I miised the Cruze as the loaner was a dog even with the ECO button turned off.


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## grs1961 (Oct 23, 2012)

The dealer misled you slightly, it's not that the code will clear after 7 starts, it will clear after 7 starts if id does not reoccur.

It's a countdown timer, so, after 4 starts, when it happens again, back to 7 goes the counter, and so on.

That said, they should not have just cleared the code, they should at least have told you what is causing it (my Korean-built diesel throws a couple of P02e1 codes every 10 000 km or so, we know it's just a flap that gets stuck once in a while and it clears after a few days, when I get it serviced I ask them to run the diagnostic for that code just to be on the safe side).


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## sx sonic (Nov 25, 2013)

Most people that are running a catless downpipe have seen that code atleast once, It's a "catalyst effeciency, low performance" code, in simple terms the computer sees the cat isn't doing its job.

You may have a bad catalytic converter. I can't think of too many other causes for that code. An airleak before the second O2 sensor could cause it, the others are very unlikely, a PCM fault.

Dealer hopefully won't take long to fix it.


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## fj40intow (Nov 4, 2013)

update: dealer called at end of day. They want to keep care longer as they have not found root cause.


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## KpaxFAQ (Sep 1, 2013)

Didnt the other poster with this code have their O2 sensor replaced?


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## Robby (Mar 1, 2013)

KpaxFAQ said:


> Didnt the other poster with this code have their O2 sensor replaced?


Yes.....and some kind of exaust filter too..

Rob


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## Chevy Customer Care (Oct 29, 2011)

fj40intow said:


> update: dealer called at end of day. They want to keep care longer as they have not found root cause.


Hey fj40intow,

If this is something you would like us to look into for you, feel free to reach out via PM. Please include your full name and contact information, VIN, current mileage, and involved dealership. 

Sincerely, 

Jonathan A. (Assisting Erica)
Chevrolet Customer Care


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## diesel (Jun 8, 2013)

fj40intow said:


> update: dealer called at end of day. They want to keep care longer as they have not found root cause.


Keep us posted. I was mistaken about the code that was in another thread, you are the (un)lucky first person to have this code on a diesel.


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## fj40intow (Nov 4, 2013)

I got the car back.
The mechanic was advised to do a manual regeneration and then smoke test the intake system.
They found a airleak at the PCV oil separator assembly. He sealed the assembly to the air cleaner outlet duct.
They also found and installed updated calibration for ECM concerning exhaust after treatment.
They test drove 200 miles over 3 days.

Wish me luck!


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## Robby (Mar 1, 2013)

AWSOME!

Sounds reasonable.......keep us in the loop and congrats on getting it back.
At least your dealer took the time to verify the repair......some could learn from this.

Rob


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## diesel (Jun 8, 2013)

Yes, glad to hear you have it back. Sounds like your dealer did some good diagnosis on it. Sounds like they want to get it right. I am wondering abotu the ECM update - my car has never had any updates, and now I wonder if it needs one. It runs fine though.


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## giantsnation (Oct 11, 2012)

Just got this code and my dealer said without hesitation - oh, 420 code that's the catalytic converter for sure. I have an appointment to get the new one installed on Wednesday. My dealership was actually nice and good about this because I'm very close to 36K (even though the actually cat is covered up to 8 years, subsequent damage would not have been).


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## Chevy Customer Care (Oct 29, 2011)

giantsnation said:


> Just got this code and my dealer said without hesitation - oh, 420 code that's the catalytic converter for sure. I have an appointment to get the new one installed on Wednesday. My dealership was actually nice and good about this because I'm very close to 36K (even though the actually cat is covered up to 8 years, subsequent damage would not have been).


Hey there,

Glad to hear that everything seems to be going smoothly so far. Please be sure to update us soon on the outcome of your appointment. I'm happy to help if you need any additional assistance as well! 

Patsy G
Chevrolet Customer Care


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## fj40intow (Nov 4, 2013)

Update: the car is back in the shop after the 5th CEL. They gave me a 2014 Cruze LT with a gas motor. Boy what a difference! I miss the Diesel!
Anyway, I guess I am one of the handfull that has problems. I do hope they can get it correct soon.


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## Chevy Customer Care (Oct 29, 2011)

fj40intow said:


> Update: the car is back in the shop after the 5th CEL. They gave me a 2014 Cruze LT with a gas motor. Boy what a difference! I miss the Diesel!
> Anyway, I guess I am one of the handfull that has problems. I do hope they can get it correct soon.


Hey there,

Be sure to keep us all updated, and let me know if you need any further assistance with anything. I am truly sorry for the reoccurring CEL concerns, but I hope this last visit will fix it for good. Looking forward to hearing from you soon.

Patsy G
Chevrolet Customer Care


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## fj40intow (Nov 4, 2013)

Update: the car is still in the shop. I miss the diesel. They gave me a gasser Cruze to drive. I miss the power, the brakes, and the ride. I miss the fuel mileage. The gasser gets 34 vs 44 on the same stretch.
Yes, there is a difference.


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## smallheadz (May 11, 2014)

No you are not the only one . We have been driving ours for a month with a CEL because of a back ordered part. Really? No loaner no nothing "just be patient" they say (they meaning the dealership and customer service reps on here). I have stated this in multiple threads on here , how patient do we have to be? This is for a NOX sensor- god forbid something major happens.


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## Scott M. (Apr 23, 2013)

I have been driving a gasser cruze for a month now also. Because they are giving me a free loaner and doing everything under warranty they think there is no hurry or no urgency. If I wanted a gas cruze I would have bought one. They really have no clue how to fix it. They are just changing parts and each part takes weeks to get.


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## smallheadz (May 11, 2014)

Sound like an echo of my story. I called dealer today and said if my parts are not in then call and find out something. Someone has to know pick up the phone and call. I left this voicemail at my local GM service where my car was bought and serviced, needless to say I never got a call back


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## diesel (Jun 8, 2013)

You guys have seem to have lemon law cases if you want them. I can tell you they are not fun, but neither is a problematic car. I am a big fan of the Cruze diesel and my experience has been very good, but as with any good car, especially one with a smaller knowledge base, some can have problems, and some of the problems can be elusive, and in turn a real PITA for the owner.


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## Scott M. (Apr 23, 2013)

The lemon laws in NJ are only good up to 24,000 miles. Maybe I can get around that but I already racked up 47,000. Not a single problem other than emissions crap. If I could only delete all this stuff I would have an awesome car.


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## fj40intow (Nov 4, 2013)

Well I got my diesel Cruze back after two weeks in the shop.
I learned two things:
1. A gas Cruze is no substitute for a Diesel cruze.
2. GM still cannot find out why I have a CEL for emissions 5 times since I bought this car!

I am totally happy with the car, just miffed about the CELs.
I commute 72 mile each way to work. Am I parking my car in the middle of a regen? If so why doesn't GM put an indicator somewhere to let us know a regen is in process? Anyway, the last dealership tried hard and I will revist them again.


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## grs1961 (Oct 23, 2012)

During a regen the idle speed rises by about 100rpm, which is a good indicator.

If your DIC can do instant reading on fuel economy, setting it to metric and learning what values are shown on various sectoins of your usual drives helps - I am fortunate in that I have several slopes where I see "0.0" in normal conditions, but it jumps to "3.x" when a regen is occurring.

That's a major give-away, seeing 3.x or 5.x when you expect to see 0.0 or 0.5 or 2.7.


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## Scott M. (Apr 23, 2013)

I think the reason GM doesnt give any regen info is because they want to downplay the diesel engine and promote the MPG numbers. After all they dont even put the word diesel on the car. Its no wonder they dont show regen activity. Its like they are hiding it under the hood. I want to monitor soot accumulation and regen activity also.


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## Chevy Customer Care (Oct 29, 2011)

fj40intow said:


> Well I got my diesel Cruze back after two weeks in the shop.
> I learned two things:
> 1. A gas Cruze is no substitute for a Diesel cruze.
> 2. GM still cannot find out why I have a CEL for emissions 5 times since I bought this car!
> ...


Hey there,

Let me know if you experience any further concerns down the road. I would be happy to assist the best way possible. 

Patsy G
Chevrolet Customer Care


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## Su8pack1 (Apr 17, 2014)

We've had ours back twice with CEL's and have had it fixed quickly both times.


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## fj40intow (Nov 4, 2013)

Chevy Customer Care said:


> Hey there,
> 
> Let me know if you experience any further concerns down the road. I would be happy to assist the best way possible.
> 
> ...


Patsy,

The CEL came back on, OnStar diagnosed it emissions issue (again). It self cleared over the weekend.


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## Chevy Customer Care (Oct 29, 2011)

fj40intow said:


> Patsy,
> 
> The CEL came back on, OnStar diagnosed it emissions issue (again). It self cleared over the weekend.


Hi Mike,

Very sorry that it came back on! It's been almost a year since it happened previously! Glad to hear that it cleared itself, but if it becomes continuous feel free to send me a private message again. I will be sure to reach out to the dealership on your behalf again. 

Patsy G
Chevrolet Customer Care


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## Tyranttrent (Jul 31, 2014)

giantsnation said:


> Just got this code and my dealer said without hesitation - oh, 420 code that's the catalytic converter for sure. I have an appointment to get the new one installed on Wednesday. My dealership was actually nice and good about this because I'm very close to 36K (even though the actually cat is covered up to 8 years, subsequent damage would not have been).


Same code here. Changed cat. Code came back 2 weeks later.


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## albo60s (May 29, 2014)

is any of this fuel related? I buy diesel at stations that sell a lot of fuel but still have had some check engine light issues.


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## cjs (Nov 23, 2015)

HI all,

I just bought a turbo[FONT=Lucida Grande, Verdana, Arial, sans-serif] [/FONT]diesel Cruze, I got this check engine light two a couple times. It started after a oil change and the care kept going in to a regeneration every 30 to 85 miles, which causes the check engine light, the first time I took it down there the dealership replace my EG1 sensor, they told me it wasn't getting hot enough I told I don't think that was the issue, they replace it 4 days later the check engine came back, took down told them I think my be particulate filter, they told me probably not, that had engineer come down work make some adjustments still had a issue they check the diesel fluid make sure I wasn't using bio diesel or any thing crazy even thought I told them I wasn't. Three weeks later they changed the air cooler both eg sensor particulate filter and cat, the cooler and the hoses. At the end of day the issue was when they did my oil change they over filled it. They put in 5 liters when the car requires 4.5 liters, I've driven the car now 5 days no issue and went about 1200 miles. will repost if the issue comes back.


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## diesel (Jun 8, 2013)

cjs said:


> HI all,
> 
> I just bought a turbodiesel Cruze, I got this check engine light two a couple times. It started after a oil change and the care kept going in to a regeneration every 30 to 85 miles, which causes the check engine light, the first time I took it down there the dealership replace my EG1 sensor, they told me it wasn't getting hot enough I told I don't think that was the issue, they replace it 4 days later the check engine came back, took down told them I think my be particulate filter, they told me probably not, that had engineer come down work make some adjustments still had a issue they check the diesel fluid make sure I wasn't using bio diesel or any thing crazy even thought I told them I wasn't. Three weeks later they changed the air cooler both eg sensor particulate filter and cat, the cooler and the hoses. At the end of day the issue was when they did my oil change they over filled it. They put in 5 liters when the car requires 4.5 liters, I've driven the car now 5 days no issue and went about 1200 miles. will repost if the issue comes back.


Welcome to the forum! it's not the first time a dealership has screwed up an oil change. And I have found from experience that 4.5 quarts pretty much fills it up. When I was putting the 4.75 quarts (or, about 4.5 liters) it always looked overfilled to me. I never had any issues though. Make sure they put Dexos2 oil in!


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## Duramax_7 (Nov 26, 2015)

P0420 checks the health of the catalyst by injecting raw fuel into the catalyst and checking for a temperature rise on the EGT sensor downstream of the catalyst. It should only set if catalyst is melted (very rare), poisoned (possibly from oil), or plugged with soot.


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## NickD (Dec 10, 2011)

P0420 is also a gas engine code, good question how this relates to a diesel without the shop manual to explain it. From the gas shop manual.

"A 3-way catalyst controls emissions of hydrocarbons, carbon monoxide (CO), and oxides of nitrogen (NOX). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbon(s) and the CO that are present in the exhaust gas. This process converts the hydrocarbon(s) and the CO into water vapor and carbon dioxide (CO2), and reduces the NOX, converting the NOX into nitrogen. The catalyst also stores oxygen. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the three way catalyst. The HO2S 2 produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emissions efficiently. The ECM monitors the efficiency of the catalyst by allowing the catalyst to heat, then wait for a stabilization period while the engine is idling. The ECM then adds and removes fuel while monitoring the HO2S 2. When the catalyst is functioning properly, the HO2S 2 response to the extra fuel is slow compared to the response of the HO2S 1, which is located before the three way catalyst. When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold."

News to me, wasn't even aware of a good NOx catalytic converter.

Conditions for setting the code for gas are. 

"The ECM has determined the catalyst efficiency has degraded below a calibrated threshold. 


This diagnostic may conclude in 6 test attempts which will require at least 2 drive cycles. However, this diagnostic may require as many as 8 test attempts. Depending on driving conditions, more than 2 drive cycles may be required. Each test attempt may conclude within approximately 1 min."

Things to inspect if this code is set:



An engine misfire
High engine oil or high coolant consumption
Retarded spark timing
A weak or poor spark
A lean fuel mixture
A rich fuel mixture
A damaged oxygen sensor or wiring harness

Of course a weak or poor spark wouldn't apply, but a plugged or a misfiring injector sure would and fuel injectors are also timed and do have dwell.

A real common problem with setting these codes is water in the fuel, whether its gas or diesel, talking to an old farm boy on this issue. Another real problem is only using one O2 sensor, with only one misfire, it doesn't know what in the hail to do. Sees excess oxygen and thinks the rest of the engine is running lean. Its response to this is nothing short of stupid. Enriches the fuel that could burn up a cat in a hurry.

That second O2 sensor is practically next to worthless, suppose to follow the first, really only good for detecting leaks in the exhaust. But typically get more exhaust noise with this you can hear. 

This code is also a so-called type A code, only needs to misfire once to be set. So can be a very erratic condition.

If an injector completely fails, or one spark plug, you will certainly notice a huge difference in performance, but with occasional misfiring, looking for a needle in a haystack. I like checking for water in the fuel first, sure a common problem around here. Never was a good idea to bury fuel tanks in the ground with all that ground water around here. 

Where are you from?


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## NickD (Dec 10, 2011)

Ha, back in the good old days, all vehicle were equipped with one of these.










Some vehicles still have one of these today, with just one glance you could tell if you had water in your fuel.

Some even have a drain.










For a quick cure, forgot about these, see they still sell these in the aftermarket. Should install these on my own vehicles.


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## Duramax_7 (Nov 26, 2015)

NickD said:


> P0420 is also a gas engine code, good question how this relates to a diesel without the shop manual to explain it. From the gas shop manual.
> 
> ...


Those are two completely different diagnostics... They (gas and diesel) only share the P-code. 

The O2 sensor is not used for diesel catalyst diagnostics. They use the EGT sensors as described above.


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## diesel (Jun 8, 2013)

NickD said:


> Ha, back in the good old days, all vehicle were equipped with one of these.
> 
> 
> 
> ...


The diesels have both of these features - sort of. There is a sensor that will tell you if you have water in the fuel and they do come with a drain from the factory.


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## Marshall (Dec 26, 2015)

NickD said:


> P0420 is also a gas engine code, From the gas shop manual.
> 
> "A 3-way catalyst controls emissions of hydrocarbons, carbon monoxide (CO), and oxides of nitrogen (NOX). The catalyst within the converter promotes a chemical reaction, which oxidizes the hydrocarbon(s) and the CO that are present in the exhaust gas. The engine control module (ECM) monitors this process by using a heated oxygen sensor (HO2S) that is in the exhaust stream after the three way catalyst. The HO2S 2 produces an output signal that the ECM uses to calculate the oxygen storage capacity of the catalyst. This indicates the ability of the catalyst to convert the exhaust emis When the HO2S 2 response is near that of the HO2S 1, the oxygen storage capability and efficiency of the catalyst may be degraded below an acceptable threshold."
> 
> ...


My 2014 Cruze (gasser) has just started throwing this code @ 24K My question is how much of the repair cost will be covered under the 8yr/80k warranty?

(still looking for the other thread)


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## Robby (Mar 1, 2013)

Check answer in your first post.

Rob


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## Chevy Customer Care (Oct 29, 2011)

Marshall said:


> My 2014 Cruze (gasser) has just started throwing this code @ 24K My question is how much of the repair cost will be covered under the 8yr/80k warranty?
> 
> (still looking for the other thread)


Hello Marshall,

We would be happy to look into that for you and get in touch with the dealer if needed. Please send a private message with your VIN, contact information, current mileage, and preferred Chevrolet dealership.
We are looking forward to your message.

Cecil J.
Chevrolet Customer Care


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## Marshall (Dec 26, 2015)

Chevy Customer Care said:


> Hello Marshall,
> We would be happy to look into that for you and get in touch with the dealer if needed. Please send a private message with your VIN, contact information, current mileage, and preferred Chevrolet dealership. We are looking forward to your message.
> Cecil J. Chevrolet Customer Care


Couple PM's sent


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