P0299 Underboost CEL and questions

[humphrey111]

Last week the check engine light came on in my '12 Sonic LT MT. I took it to the "zone" and had it scanned since I don't have one. P0299 Underboost. A bit concerning, but I know there are alot of things that can cause this. I cleared the code and waited to see if it came back. Did a little reading on here and and see that it seems to be fairly common and there is even a TSB on it. Now, I'm wishing I hadn't cleared it, since the dealer won't do anything if the light isn't on.

A little background on the car and how I drive... I bought this car because I drive 120 miles a day for work, but I still wanted something that was fun to drive. I would say 90% of the time I'm driving conservatively, barely even building any boost. So I'm not really sure how long this has been going on. The car is still stock.

A guy I work with does tuning on SRT-4's and others and he lent me a Diablo Trinity so I could monitor and log what was going on. First day monitoring boost, all seemed fine until about halfway home. Leaving a construction zone, I noticed I wasn't going over 5 PSI of boost. Next day, no issues, boost 10-15 PSI. All seemed fine for about 4 days. Then yesterday, nothing over 5 PSI the whole way home. Today on the way in, no issues. The Diablo shows me that P0299 is pending but the car hasn't thrown the light on yet.

Time for questions.
1. How long before the car throws the light on after the diablo detects it? I kept dropping to 3rd and accelerating on the way home yesterday to try and speed up the process, and to see if it would start making boost gain.

2. I have put 50k+ miles on this car in 2 years and it had 40k when I bought it, I am sitting at 93700. My chevy warranty website says my car is still covered on the limited powertrain warranty (getting close though). Would/Should this be covered?

3. If it isn't covered, what are my options here? I've seen that this is typically a wastegate issue. Is it something I can fix without replacing the whole turbo assembly? I haven't yet checked to see if there is excessive play in the linkage.

 

[spacedout]

If its the Turbo causing the issue its covered by the 5 year 100K powertrain warranty, I have seen a few post with the same code and typically that is what the problem is.

 

[Maddmatts]

I find that the interval between P0299's 'pending' to 'check engine' seems to be based on distance travelled and only if the problem persists the entire time. The turbo should still be covered under the powertrain warranty.

When you bring it to a dealership, make sure that Diablo tuner is not in the car. If they find it, they may use it as an excuse to void the warranty. Also don't pull off any of the vacuum lines on the wastegate actuator as it will break the witness marks on them which will also void the warranty.

The 5psi limit might also point to the bypass/recirculating valve. If it doesn't get boost pressure from the intake manifold then it will get forced open at 5psi.

 

[humphrey111]

I find that the interval between P0299's 'pending' to 'check engine' seems to be based on distance travelled and only if the problem persists the entire time. The turbo should still be covered under the powertrain warranty.

I'll just keep monitoring it and hope the CEL comes on soon.

When you bring it to a dealership, make sure that Diablo tuner is not in the car. If they find it, they may use it as an excuse to void the warranty. Also don't pull off any of the vacuum lines on the wastegate actuator as it will break the witness marks on them which will also void the warranty.

I won't be touching anything as long as it is still covered by the powertrain warranty.

 

[humphrey111]

So I've been driving this thing everyday and it's still acting up, but no light has come on yet. Not sure if this is heat related or what. I've never had the car not build boost right after I start it up and take off. It always seem to happen on my drive home at some point.

Today, driving into work I actually felt and saw my boost cut out while driving. While getting on the interstate I watched the intake pressure drop from 26 down to 18 and the car just fall on it's face. Not like bucking and sputtering, but just total power loss.

Something is definitely wrong here and I have less than 6k miles left until my powertrain is up and this thing will not turn the light on.

 

[AdorableKaren]

I'm in the same boat. My FI told me to turn off the light and that my car was fine. I have not seen the light come back on but I am very concerned something is wrong with my car. I don't have a boost gauge so I can't keep track of drops in boost. I am at the dealership now so they better fix or replace something. I know I did not drive an hour and waste my day for them to tell me nothing is wrong. Next time I'm not listening to my FI haha I'm keeping the cel on no matter what.

 

[RMinNJ]

Yeah, always keep the CEL on for the dealer. They need codes.

you need an ultragauge but all you may see is boost low...not the reason why.

I think low boost could be the wastegate rod or leak ?

 

[ScarabEpic22]

Something's going on for sure, Intake pressure of 26psi tells me there's a Trifecta tune on there BUT if the car is indeed stock, it's overboosting like crazy and the ECM is unable to control boost. Then is shuts down and forces 18psi (about 3.5psi of boost) as limp mode. My guess as to whats happening, but without a log or more info IDK for sure. Sounds like dealer time.

 

[AdorableKaren]

I have turned off codes in the past. The dealership has had no problem seeing old codes. Took about an hour to assess my sonic. The dealership is ordering a new turbo and I am getting it replaced on Monday. For free under warranty even with all my mods.

I do strongly suggest for this particular CEL to leave it on! Some dealerships will turn you away if no codes are visible. And this code did not turn back on even after a few days of driving it.

 

[RMinNJ]

Related question. ..can the ultragauge read a p0299? Or do I need some more advanced scanner?

Karen that's a great dealer you have..mine is not so intelligent.

 

[ScarabEpic22]

Yes, thats a regular DTC code any OBDII scanner can pick up.

 

[RMinNJ]

Yes, thats a regular DTC code any OBDII scanner can pick up.

Thanks ...I found the menu on my ultraguage where is supposed to show troublecodes and pending codes.

 

[humphrey111]

Something's going on for sure, Intake pressure of 26psi tells me there's a Trifecta tune on there BUT if the car is indeed stock, it's overboosting like crazy and the ECM is unable to control boost. Then is shuts down and forces 18psi (about 3.5psi of boost) as limp mode. My guess as to whats happening, but without a log or more info IDK for sure. Sounds like dealer time.

Absolute intake pressure. Take away 14.6ish PSI for atmospheric and you get 11-12 PSI of boost. That's not overboosting.

Still gotta get the car to turn the light on before I can take it in.

 

[Kirvus]

I am only getting this cel when I am using the canned Diablo tune. I don't want to take it to the dealership with it still tuned so I took the tune off and hence, no cel. Since no cel, the dealership won't look at it. So the question is do most of you just keep your car tuned when you have taken it to the dealership for this?

Sent from my Nexus 7 using Tapatalk

 

[RMinNJ]

I am only getting this cel when I am using the canned Diablo tune. I don't want to take it to the dealership with it still tuned so I took the tune off and hence, no cel. Since no cel, the dealership won't look at it. So the question is do most of you just keep your car tuned when you have taken it to the dealership for this?

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That stinks..cause it could be a boost leak or waste gate rod that only the tuneprovokes.. To me is seems why Chevy went so conservative on the tuning.

No idea how to chase a boost leak down...maybe someone has some ideas.
Ditto for the wastegate.

I guess flashing it back to stock clears the codes??

 

[Kirvus]

Sure enough does. Last week I started to get shutter and rough at idle, I had 3 codes: p0171, p1101, and p0299. The p0299 has been there for months. All codes cleared when I took the tune off. The p0171 and p1101 came back before taking it in to the dealership where there was a leak on the manifold. I still have the tune off and driving like I stole it..hoping that might trigger the code..nothing yet.

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[goatnik]

Hello guys and gals here goes my first post.
I also had 0299 code come up a day or two after I poured a bottle of Lucas injector cleaner/cylinder lubricant in the fuel tank. I don't know if that is a coincidence or not. I read other threads and everybody is talking about turbo wastegates, air leaks, spark plugs/coils... Is it possible that fuel additive caused the code?
I cleared the code a week ago, added fresh fuel after that and I don't see it coming back yet. Hopefully it stays like that

 

[humphrey111]

Ok, so my CEL finally came back on, after weeks of it being pending. Got an appointment Monday. Really hoping they fix this under limited powertrain and I don't have to fight them on it.

I though I read somewhere that there is a TSB on this underboost problem. Should I have that in my back pocket in case they try to say that this isn't something that's covered?

 

[Maddmatts]

If your powertrain warranty is still valid, the diagnostic and repair should be covered.

A TSB will not guarantee a freebie. It's not the same thing as a recall.

The Sonic/Cruze TSB for P0299 brings attention to possible excessive wear on the wastegate linkage pin and recommends replacement of the turbo/exhaust manifold assembly if found to be the case.

 

[humphrey111]

Light went back off. They said they can still pull the code if it's been on recently. Taking it in later today.

This underboost problem is so weird. I don't really understand what is happening. The other day I really noticed the lack of power and knew it wasn't boosting right so I pulled off and shut off the car. Restarted and pulled back on the highway with good boost again. How can mechanical wear of some linkage be the cause of this? I wouldn't think it would come and go if it was a mechanical problem.

4k left until 100k miles (and i drive 120 miles a day), I just want to try to get it fixed before my time is up, and I'm afraid this is going to drag out until my warranty expires.