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Discussion Starter · #21 ·
The light magically disappeared yesterday, so it's looking like a transient thing. I'm going to take some down time to clean the EGR valve if I can and see what is going on there.
 

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2018 Cruze Hatch Diesel Manual
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I've had a transient CEL as well over the past few weeks. I got P2457: EGR low efficiency. It went off for about an hour, came back on, then went off after I let the car sit for a week while I was away on vacation. I also had the warranty replaced EGR, which was a joy and a half.
 

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I've had a transient CEL as well over the past few weeks. I got P2457: EGR low efficiency. It went off for about an hour, came back on, then went off after I let the car sit for a week while I was away on vacation. I also had the warranty replaced EGR, which was a joy and a half.
The EGR flow is mostly based off MAF.
 

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Discussion Starter · #24 ·
The EGR flow is mostly based off MAF.
Interesting, but not surprising. I doubt there is a sensor to measure EGR flow, so it's all calculated on how much air is flowing through the MAF sensor. Open up the EGR valve and the ECU expects less through the MAF because of the extra air volume coming from EGR. There has to be some logic to it that checks how much the flow is and then throws a CEL if the expected airflow isn't being achieved.
 

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Discussion Starter · #29 ·
Just a theoretical question here for those who know: What happens if you install a block-off plate in the EGR?

Does it simply illuminate the CEL and that's all? Or do you get warnings that count down to speed restrictions?
 

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Just a theoretical question here for those who know: What happens if you install a block-off plate in the EGR?

Does it simply illuminate the CEL and that's all? Or do you get warnings that count down to speed restrictions?
If you unplug it: A CEL (assuming there is no CURRENT countdown).
If you block it without unplugging: I have no idea.
If you unplug and BLOCK: Same as just unplugging, it.


This is because the EGR Diagnostic takes precedence over the SCR. As such, the SCR diagnostics will never run. And you don't get a countdown.... That's just how GM/Bosch programmed it....

Soooo yeah you can kinda bypass the emissions this way.

For the most part the DPF can function without EGR. It just takes longer to warm up on cold start.
 

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Discussion Starter · #38 ·
The light came back again!

I think I figured it out. I was going somewhere for an appointment and it was raining, and I sat in the car at idle (with the A/C on to keep humidity down) for about 20 minutes. After that, driving away, the light came on.

The prior time was when I was taking my mom on errands and we were stuck in the Wendy's drive-thru for a serious 20 minutes. It was while they were transitioning from breakfast to lunch, and this Wendy's isn't very efficient or well-staffed in the first place. Anyways, after idling, the light came on during the next drive.

It appears that idling has some soot clogging up the EGR valve and it triggers the light the next time I drive the car (when the ECU detect low EGR flow due to the soot clogging it). Any highway driving in the following days must blast it out of there and then the light goes off after a while.
 

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Discussion Starter · #40 ·
Could it be a leaky injector? What would cause that much soot? Just idling causes massive soot? Sounds like the map is messed up?
I don't know, but that seems to be the recent pattern. The time prior to these two recent CELs was it coming on when I was doing highway driving, so I assumed it was kinda random. These last two times have been immediately after idling for some period of time (about 20 minutes each time). I left the Wendy's drive-thru, took my mom to her nail appointment, and when we left the CEL came on. I left the place where I was idling in the rain waiting for it to fall off, and when I left after the appointment the CEL came on.

Nothing significant happens when the light is on, so I really don't care about it. I'm not going to fix it right now. If it gets to where I have countdowns to speed restriction, I'll probably invest the money in tuning the car to eliminate the EGR problem. Once tuned I'll find a weekend where my cousin and I can yank the intake manifold to do a complete cleaning and maybe remove the swirl flaps as well, if that's easy to cut them out of there and block off any possible holes.
 
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