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Discussion Starter · #1 ·
hey guys. Lurked here for a couple years but honestly never had much need for it as my car was bulletproof for a long time. Much like the rest of the world it seems to have lost its mind this past year, but I’ve kept fixing it as the used/new car markets are as awful as I can remember.
Anyhow the latest and greatest was a dpf & underboost warning. Replaced the turbo and have had the dpf manually regenerated twice. I cannot relay enough how gutless it is now, and the scanner would suggest boost is indeed way low. The dpf is also accumulating soot at an alarming rate but it’s running so crappy I’m not surprised.
Any best guesses as to what could be causing my P0299 with a brand new turbo. I’ve gone over everything twice and can’t seem to find a vacuum leak anywhere, but I’m open to any and all suggestion.
 

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Here’s my diagnosis: Intercooler Air Inlet Hose and Intercooler Air Outlet Hose, P/N 95472183, 13247992, 22979688, 19420422.

Replace these and force another regen. All should be well after this.
 

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Discussion Starter · #3 ·
Here’s my diagnosis: Intercooler Air Inlet Hose and Intercooler Air Outlet Hose, P/N 95472183, 13247992, 22979688, 19420422.

Replace these and force another regen. All should be well after this.
I l appreciate the quick response. I’m going to have the mechanic take a look at the intercooler hoses while he’s at it
 

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Discussion Starter · #4 ·
Update, the inlet hose is special order and the dealer isn’t sure when id be able to get one. I did change the map sensor as the existing one had partially melted in the intake. I still get P0299 but it comes up much faster now. Not surprising, I’m amazed the old map sensor was producing a reading at all in the shape it was in.
Any chance I could be losing boost somewhere else? I’m all for changing the intercooler hoses but this is my daily driver and waiting for them to become available is going to really complicate things for me. I’m showing anywhere from 7-8 psi boost under throttle. It’s clearly lacking power. And around 2-5 psi vacuum at idle. I’m assuming that part is relatively normal but I haven’t really seen anyones baseline boost numbers in my searches.
 

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I always had a scan gauge to monitor regens and what not and at idle typically MAP was 14.7psi which is atmospheric pressure (or 0psig). The only time I had a vacuum (less than 14.7psi) was during regens otherwise it was always positive pressure IIRC.

Before replacing any more parts I would first visually check all the charge pipes/connections for any leaks from turbo to intake manifold. When I first got my car the charge pipe disconnected from the intake which resulted in underboost/dpf full/gutless pig. Check any rubber hoses leading in/out of the PCV system. Also check your air filter/MAF/intake pipe and make the filter is clean and there's no obvious blockage. Check the turbo solenoid and line going to the turbo, make sure they're connected correctly/not cracked, split or clogged. It is a VGT so I imagine if the vanes aren't being actuated then it might have trouble making boost.

I'm not familiar with any posts regarding a cracked intake manifold but you gotta be losing boost somewhere 🤔 also I'm not sure if the throttle valve or EGR would have any role in this, but it might be worth disassembling/cleaning them if you have a lot of miles.

You're definitely on the right forum though, there's a lot of really knowledgeable members here, especially with the gen1 diesel!
 
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VGT actuator failure, vacuum leak, vacuum pump failure, or brake booster failure. Very common problem on high mileage diesels. Brakes may or may not be affected.

Leads to underboost. Looks like a turbo failure. Causes Regen failures.

Many people replace the turbo over this. Turbo is fine.
 

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Update, the inlet hose is special order and the dealer isn’t sure when id be able to get one. I did change the map sensor as the existing one had partially melted in the intake. I still get P0299 but it comes up much faster now. Not surprising, I’m amazed the old map sensor was producing a reading at all in the shape it was in.
Any chance I could be losing boost somewhere else? I’m all for changing the intercooler hoses but this is my daily driver and waiting for them to become available is going to really complicate things for me. I’m showing anywhere from 7-8 psi boost under throttle. It’s clearly lacking power. And around 2-5 psi vacuum at idle. I’m assuming that part is relatively normal but I haven’t really seen anyones baseline boost numbers in my searches.
If I remember correctly, I was seeing boost numbers of 18-23psi when I watched the numbers on torque pro, and I've never seen it drop into vacuum. Checking the vacuum pump and lines, vgt actuator, and the vac lines from the actuator to the turbo are very good advice. Also if you have Torque, Gretio, or a scanner that can watch live data, watch the commanded and actual vane position for the vgt to see if it's actuating as commanded. If the throttle body can't open due to being clogged with soot or due to a mechanical failure, that would definitely cause underboost too. Showing vacuum at idle also seems to be a good reason to look into a throttle body problem. It seems like it would throw a code of its own if it wasn't performing as commanded, though.
 

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If I remember correctly, I was seeing boost numbers of 18-23psi when I watched the numbers on torque pro, and I've never seen it drop into vacuum. Checking the vacuum pump and lines, vgt actuator, and the vac lines from the actuator to the turbo are very good advice. Also if you have Torque, Gretio, or a scanner that can watch live data, watch the commanded and actual vane position for the vgt to see if it's actuating as commanded. If the throttle body can't open due to being clogged with soot or due to a mechanical failure, that would definitely cause underboost too. Showing vacuum at idle also seems to be a good reason to look into a throttle body problem. It seems like it would throw a code of its own if it wasn't performing as commanded, though.
I don't know how the CTD measure VGT position. It seems to be modelled somehow. So, I wouldn't fully trust it and would not expect a code.

edit: What I mean by this is the position sensor is the vacuum actuator itself. I have no idea how this works. Other newer diesels have a dedicated sensor and an electronically controlled actuator... But the Cruze has this vacuum monstrosity diaphragm system.
 

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I don't know how the CTD measure VGT position. It seems to be modelled somehow. So, I wouldn't fully trust it and would not expect a code.

edit: What I mean by this is the position sensor is the vacuum actuator itself. I have no idea how this works. Other newer diesels have a dedicated sensor and an electronically controlled actuator... But the Cruze has this vacuum monstrosity diaphragm system.
Yeah. I'm not sure how it senses command vs actual, but I do know that it has both PIDs, and they seem to read independently of one another.
 
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