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Had this pop up on me on the way home from work yesterday. Able to get home and its showing 20 miles before my first reduction. 2014 with 142k miles. It has had the Nox and DEF tank recall done last year. I took this car over from my wife about a month ago when I bought her a 4 Runner. Her commute is about 30 mins of interstate each day. Mine is over an hour each way running 70-75 mph for at least an hour of that, for what that info is worth. Most of the miles on this car is running at interstate speeds, not a lot of stop and go use.

Is there anyway for me to reset this fault? I have an OBS cable for a my laptop, Im able to clear the CEL but not showing any way to clear this fault.

So I've read over all the post I could find on here and other places about this issue. So far it doesn't seem like there is a good explanation on how to resolve this issue. Best I've found so far is it caused by a difference or problem between the Nox 1 and Nox 2 sensor. Im showing them between 150-200 each online. I hate to throw $400 at a maybe... The other resolutions I've seen are people running the car at WOT for a time to try an burn/clear out any soot in the system, after adding or replacing the DEF fluid. I ran my cruze at around 3k RPMs for about 15-20 mins last night on the way home after getting this fault. Added more DEF fluid at the house (it was low) and did the same for another 10 mins or so with no change. I cant bring myself to floor the car in hopes it "might" fix the issue, my luck I'll do nothing but blow up the engine. So I'm not sure what to do from here. Everything is out of warranty, so if I take it to the dealership I know Ill get hit with $1k or more in repairs, my local dealership seem like good people but all dealerships are way overpriced for repairs. I could pull the DEF tank, flush and add more fresh fluid, shouldn't be to hard to do. I could go ahead and drop the $1500 for a delete and tune, would that clear up this issue? Seems like it would being is takes are of all the parts causing this issue, but I'm not seeing the delete/tune kits online any longer.

Any advice would be appreciated
 

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Not sure about how best to clear the code, it may require a visit to the dealer.

Delete will definitely re-program/clear codes if you’re lucky enough to find one still available.
 

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I'm going to check it again when I get home, run it down the road and see what happens. If that doesn't do anything I'm thinking about disconnecting the battery over night and see if that does anything.
 

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Reverend Red Bull
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Are there any OBD codes appearing beyond the Poor DEF Quality message? If so, what were the fault codes? If you have codes, they will help narrow the source of the problem. If you have the DEF message, but no codes, you're probably looking at a clogged or failed DEF injector, or a NOX2 sensor that is giving a bad reading, but hasn't completely died to set the NOX2 code.

It's almost never an actual problem with the DEF itself, especially if you have since topped off with fresh. A lack of DEF entering the system due to a clogged or failed injector will cause the same kind of NOX sensor readings that bad DEF would cause, though, so it can set off the Poor DEF Quality message.

If you have stock emissions, then there is no particulate matter making it back to the NOX2 sensor to clog it up, and if you're getting a poor DEF message from a NOX sensor issue, it's almost always NOX2 and not NOX1 causing it. So, doing the Italian Tune Up method isn't going to genuinely do anything to burn off anything on that sensor. In my experience, sometimes the Poor DEF Quality message will appear intermittently before it eventually sets permanently. So, I think people clearing the DEF message with running the engine hard are just experiencing a coincidence, and it will return, whether it takes a week and a couple hundred miles, or a few months and 10,000 miles, as the underlying fault becomes more consistent.
 

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Discussion Starter #5
Are there any OBD codes appearing beyond the Poor DEF Quality message? If so, what were the fault codes? If you have codes, they will help narrow the source of the problem. If you have the DEF message, but no codes, you're probably looking at a clogged or failed DEF injector, or a NOX2 sensor that is giving a bad reading, but hasn't completely died to set the NOX2 code.

It's almost never an actual problem with the DEF itself, especially if you have since topped off with fresh. A lack of DEF entering the system due to a clogged or failed injector will cause the same kind of NOX sensor readings that bad DEF would cause, though, so it can set off the Poor DEF Quality message.

If you have stock emissions, then there is no particulate matter making it back to the NOX2 sensor to clog it up, and if you're getting a poor DEF message from a NOX sensor issue, it's almost always NOX2 and not NOX1 causing it. So, doing the Italian Tune Up method isn't going to genuinely do anything to burn off anything on that sensor. In my experience, sometimes the Poor DEF Quality message will appear intermittently before it eventually sets permanently. So, I think people clearing the DEF message with running the engine hard are just experiencing a coincidence, and it will return, whether it takes a week and a couple hundred miles, or a few months and 10,000 miles, as the underlying fault becomes more consistent.
Took it for a drive today to pick up my daughter and no change. It hit the 100 miles so now Im reduced to 65mph. It has had a P20E4 code for awhile. I changed an O2 sensor for this code (the up stream sensor near the top) and it will go away for a while then come back. Today it is showing a new code that I've never seen. P0420. When this problem first started a few days ago I checked the codes and cleared them trying to reset this fault and the P20E4 was the only code listed. Today on the way home the CEL came back on and it is showing both these codes. So maybe its the same O2 sensor again? Maybe the one I replaced it with was bad?
 

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your fluid isnt bad, dont waste time changing it/flushing it

you dont need WOT to burn/regen, one gear down is plenty

if you get @Snipesy app youll be able to do a manual regen ---biscan in your app store, but this isnt your issue

you can change the sensor yourself, im unsure whether it needs the gm computer or not to reset it
 

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Reverend Red Bull
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Took it for a drive today to pick up my daughter and no change. It hit the 100 miles so now Im reduced to 65mph. It has had a P20E4 code for awhile. I changed an O2 sensor for this code (the up stream sensor near the top) and it will go away for a while then come back. Today it is showing a new code that I've never seen. P0420. When this problem first started a few days ago I checked the codes and cleared them trying to reset this fault and the P20E4 was the only code listed. Today on the way home the CEL came back on and it is showing both these codes. So maybe its the same O2 sensor again? Maybe the one I replaced it with was bad?
P20E4 is Exhaust Gas Temperature Sensor 2/3 correlation (so nothing to do with your O2 or NOX sensors). The good news is they're way cheaper than NOX sensors and a really easy change. You can pull up EGT sensor values in the torque app or with bi-scan. Sensors 1 and 2 should be very close, with 2 being slightly lower 80% of the time. Sensor 3 should be noticeably lower than the others, but could be nearly as hot as the others if you've been running hard or in a re-gen. The one with a wonky reading (way too high or low, or pegged out a minimum or maximum, or stuck at a round number like 1200.00) will be the one that needs to be replaced. Since they're only $30-40 each, you could even throw both sensors at it if you don't have a way to scan them, or if you just want to go all-in on ruling them out. EGT2 is mid-low DPF, and EGT3 is under the car by the DEF injector.

P0420 is a code I run across all the time on gas vehicles, but never on my Diesel. On gassers, it means the catalytic converter is not working at the specified standard. I'm not sure if it is meant to reference the "Diesel Oxidation Catalyist" (top portion of our DPF unit) or the SCR (the unit where the DEF does its magic) on our cars, since both sometimes get referred to as catalytic converters at times, and "catalyst efficiency below threshold" doesn't help narrow it down. Since you have the DEF quality message set, my guess is it's related to the SCR in this instance.

Step 1 is going to be dealing with those EGT sensor(s). Since SCR does rely on input from EGT for operation, it's possible that it is metering incorrectly or becoming disabled due to the bad EGT sensor. If you're lucky, getting your EGT readings back in spec will make everything else fall into place. If not, at least you've cleared that code, and you can focus on why the SCR is not doing its job, thus setting the DEF quality message. EGT sensors do not require a computer reset like the NOX sensors (sometimes) do to clear the OBD code. If the EGT sensor fixes things, the DEFmessage will clear on its own. If the DEF message doesn't clear, then I'd go to the DEF injector next.
 

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Discussion Starter #9
P20E4 is Exhaust Gas Temperature Sensor 2/3 correlation (so nothing to do with your O2 or NOX sensors). The good news is they're way cheaper than NOX sensors and a really easy change. You can pull up EGT sensor values in the torque app or with bi-scan. Sensors 1 and 2 should be very close, with 2 being slightly lower 80% of the time. Sensor 3 should be noticeably lower than the others, but could be nearly as hot as the others if you've been running hard or in a re-gen. The one with a wonky reading (way too high or low, or pegged out a minimum or maximum, or stuck at a round number like 1200.00) will be the one that needs to be replaced. Since they're only $30-40 each, you could even throw both sensors at it if you don't have a way to scan them, or if you just want to go all-in on ruling them out. EGT2 is mid-low DPF, and EGT3 is under the car by the DEF injector.

P0420 is a code I run across all the time on gas vehicles, but never on my Diesel. On gassers, it means the catalytic converter is not working at the specified standard. I'm not sure if it is meant to reference the "Diesel Oxidation Catalyist" (top portion of our DPF unit) or the SCR (the unit where the DEF does its magic) on our cars, since both sometimes get referred to as catalytic converters at times, and "catalyst efficiency below threshold" doesn't help narrow it down. Since you have the DEF quality message set, my guess is it's related to the SCR in this instance.

Step 1 is going to be dealing with those EGT sensor(s). Since SCR does rely on input from EGT for operation, it's possible that it is metering incorrectly or becoming disabled due to the bad EGT sensor. If you're lucky, getting your EGT readings back in spec will make everything else fall into place. If not, at least you've cleared that code, and you can focus on why the SCR is not doing its job, thus setting the DEF quality message. EGT sensors do not require a computer reset like the NOX sensors (sometimes) do to clear the OBD code. If the EGT sensor fixes things, the DEFmessage will clear on its own. If the DEF message doesn't clear, then I'd go to the DEF injector next.

Well, I had a big long post with tons of questions about everything and you posted this. So this will be my first step, It will be later this afternoon before I can check these out with the scan gauge but I will look and see what I can find. I may just order both sensors and swap them out when I have time Monday or Tuesday. I swapped the EGT 1 sensor about 6 months ago and the code went away for awhile, then would come back and go away again.
 

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Discussion Starter #10
Just ordered the EGT#2 (55581034) and #3 (555810345) sensors. I replaced the #1 this summer when first started getting the P20E4 code. Figured might as well replace the other two and have all three be new parts. Amazon will have them here on Monday. Rock auto was cheaper but would be almost two weeks out. My local O'reillys could have them today but they are almost twice the price. I was unable to check the readings for the sensors and will not have time to do it until Monday. I will keep this post updated with what I find, thanks again for all the help and info. I hope this does the trick.
 
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