# 2014 2.0 LUZ (Diesel) Puzzling CEL underboost issue - P0299, P2598, P003A



## ACNeeley (May 5, 2020)

Hey guys, first time poster here. Many threads on this site have helped me greatly over the past few years, so thanks for all you do. I have had my diesel since it was brand new, so I may have some advice for others dealing with the issues I've dealt with. 

Here's my car:

2014 LUZ
199,500 miles

CEL: 

P0299
P003A
P2598
P24A5
These codes are quite intermittent. I have a bluetooth ODB scanner, with the Torque Pro app and Biscan, so I have tried a few things and reset the codes. The local dealer here saw the codes and immediately just told me the turbo is bad. I don't think they did any further investigation. I don't suspect there's anything wrong with the turbo itself, because at times the boost is just fine. Other times, it is very laggy. Particularly, when I've cleared the codes, the boost is great (builds to 20psi) until it pulls up an underboost (P0299) again, and then it lags (will only build to 5psi or so) until I clear it again. Here is what I've already done:


I pulled the intake hose off the airbox, and cleaned the MAF using the proper cleaner.
I pulled the MAP sensor, and it was extremely dirty, so I replaced it entirely. 
I pulled off the EGR valve and cleaned it up completely. I ensured it was free to open. 
I pulled off the turbo actuator solenoid, and tested the resistance. It is within the 15-19 ohm window. It (kindof) clicks when I power it with a 9V battery. I've ordered a new one of those, but I hope I can return it. 
Cleaning out throttle body today (it is quite disgusting), so I'll report if that changes anything.
Other info:

The only tests that fail on Torque Pro are labeled "MID: $85." I have no idea what that is, but everything else seems fine. 
I've read that whenever you mess with the turbo system, you need to do a turbo relearn. Could this be the issue now that I have a new MAP sensor, cleaned up EGR? Can I do this, or is that going to be something only a dealer can perform? 
Whenever these codes are popping, the gas mileage is noticeably reduced. 
Anyone have any advice? I'm about at the end of my abilities here, and I certainly can't afford a $2,000 repair for a new turbo in a car that's worth maybe $1250. 

Thanks so much in advance, and glad to be here.


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## Snipesy (Dec 7, 2015)

Or lack of vacuum. Beyond the actuator you mentioned honestly I have no idea where it gets it’s vacuum from.


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## ACNeeley (May 5, 2020)

Update:

With the bi-scan app, I am noticing that no matter the throttle position or RPMs, the "desired turbo vane position" is reading between 95% and 100%, while the "actual turbo vane position" seems more like what it should be, only going up to that level during hard acceleration. What would cause this? Bad sensor? MAP readings the car doesn't like?


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## Snipesy (Dec 7, 2015)

ACNeeley said:


> Update:
> 
> With the bi-scan app, I am noticing that no matter the throttle position or RPMs, the "desired turbo vane position" is reading between 95% and 100%, while the "actual turbo vane position" seems more like what it should be, only going up to that level during hard acceleration. What would cause this? Bad sensor? MAP readings the car doesn't like?


That's weird. It might just be the ECM trying to counter the under valued VGT positon i.e. its really suppose to be at say 70% but its at 50% so it sets it to 95% as a fail safe.

I think changing out the actuator is a good start. Maybe its overheating which would explain the intermittent behavior. If you have the tools doing a pressure test on the pipes may be useful.

If it is the turbo it will be the actual actuator in charge of moving the vanes. Thats basically a chamber which moves a rod, it's actually very similar to a waste gate setup. I unfortunately have never seen this part seperate from the turbo but on the flip side I have never heard of these things failing on a Cruze. To an extent these are cleanable but I've never done it before, let alone on a diesel Cruze.


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## ACNeeley (May 5, 2020)

Thanks...I will wait for the part and change it out when it gets here next week. In the meantime...check this out. Yuck! A lot of wet oil in there too, which tells me I may be reaching the end on this poor car...


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## Snipesy (Dec 7, 2015)

ACNeeley said:


> Thanks...I will wait for the part and change it out when it gets here next week. In the meantime...check this out. Yuck! A lot of wet oil in there too, which tells me I may be reaching the end on this poor car...
> 
> View attachment 286745
> View attachment 286746


While I agree yuck collection like this around the throttle body is normal on high mileage EGR vehicles.


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## MP81 (Jul 20, 2015)

Yup - very typical on these engines, thanks to the EGR! Nothing wrong with the engine itself. It is gross, though.

I'm basically considering that cleaning of the EGR valve and throttle valve to be regular maintenance - maybe every 50k miles or so. It's something I will be doing again here soon.


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## ACNeeley (May 5, 2020)

Well, I FIXED IT! 

After being told by the dealer I needed a new turbo, which was going to run me almost $3,000, I have fixed the underboost issue myself, and it was essentially free to fix. 

After Snipesy mentioned it may be a vacuum issue, I started looking at all the vacuum hoses I could find. There is one near the oil dipstick, under the intake snorkel that goes I'm not sure where. There's a picture below. Apparently, some tech at some point had poured oil all over this area, and the hose and the connector were covered. The oil had gotten onto the connector and the hose was slipping right off. I pulled it off and cleaned it up, then I made myself a homemade hose clamp, and voila, the actual turbo vane position began matching the desired turbo vane position, and no more CEL are being tripped. The car is also running like its brand new again. 

If I had to guess, I'd say that little hose has something to do with the EGR, as the P24A5 code is related to the EGR valve. 

BTW, I also was noticing before the fix that a boost meter would read .5 to 1 PSI of vacuum (or -0.5 to -1 boost). After I fixed it, the car is 0.0 at idle. Boost builds up to 22 psi under hard acceleration. 

Why can I figure this out and the GM master tech diesel specialist defaults to replacing the turbo, which wouldn't have even fixed the problem?? 

Anyway, thanks for your help and hopefully this helps someone else in the future as well.


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## Snipesy (Dec 7, 2015)

ACNeeley said:


> Well, I FIXED IT!
> 
> After being told by the dealer I needed a new turbo, which was going to run me almost $3,000, I have fixed the underboost issue myself, and it was essentially free to fix.
> 
> ...



Dang well done. Seems the vacuum comes from the brake booster.

The EGR Valve itself is just electronic and you can see it sticking out near the firewall. But the EGR Cooler bypass might be vacuum powered. That might be what that block is.


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## ehjorten (Jan 7, 2021)

I realize this post is 8 months old, but I am having a similar issue...P003A & P2598. I was reading this thread and was already planning on checking all of the vacuum hoses.

I wanted to add that, that connection shown in the pictures is the vacuum port from the vacuum pump assembly and the hose goes down to the EGR Valve Cooler.

There is a GM Service Bulletin PI1260 which can be found here: https://static.nhtsa.gov/odi/tsbs/2014/SB-10072144-0335.pdf

Just wanted people to have a better chance of finding it.


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## CEDOAN (Jun 1, 2021)

Snipesy said:


> Or lack of vacuum. Beyond the actuator you mentioned honestly I have no idea where it gets it’s vacuum from.


It gets vacuum from the vacuum pump assembly. It should have 26.6 inHG min.


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