2017 Mercedes Glc300 Under Boost

William Owner/Technician San Francisco, California Posted   Latest   Edited  
Question
Driveability
2017 Mercedes-Benz GLC300 4Matic 2.0L (274.920) 9-spd (725.041)—WDC0J4KBXHF194168
P0299-21 Boost Too Low

Hey guys have a 2017 glc300 with 180k. Took the car for a test drive and the scanner is showing 40 inhg which is about 20psi. But it definitely doenst feel like it. Car is blocked in right now and cant drive it with a mechanical gauge yet. Wastegate test ok, can command it on with my scanner. Diverter valve test ok, manually, snap on didnt have a output test for it. This uses an air to water intercooler with very short piping. Smoke test ok, no obvious signs of leaks from the piping. When you go WOT the car feels like it has a plugged exhaust. Removed the front air fuel ratio senor and the cat looks ok. Exahust back pressure test is also ok. Oil level was good and i also did an oil change. Thanks in advance.

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Michael Technician
Fresno, California
Michael Default
 

Dirty air filters or poor quality air filter can cause dtc. It's not a boost dtc it is a comparative dtc. Intake pressure not at correct comparative value.

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William Owner/Technician
San Francisco, California
William Default
 

Filter is good, going to drop the cat and drive it just to rule it out. It feels very sluggish under WOT.

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William Owner/Technician
San Francisco, California
William Update
 

Alldata does not have any repair info for this car. Took out the car for a spin with a mechanical gauge and its not making any boost because the wastegate is stuck open. This turbo the wastegate is open till the computer closes it. Anyone have any info on this turbo system. I cant even find a vacuum diagram for it.

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Anthony Technician
Flushing, New York
Anthony Default
 

Do you have xentry? You can test turbocharger and see if it builds boost. I’ve had a couple where wastegate jammed open.

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William Owner/Technician
San Francisco, California
William Default
 

The snap on lets me command the wastegate closed but havent tried driving it. But when i manually apply vaccum to the wastegate it wont take more than 5 inHg and the turbo wastegate is still half open at that point. Looks like the wastegate diaphragm is torn. But it doesnt look like the part is sold separately, even though it can be easily replaced. Will wire up the wastegate shut and drive it…

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Anthony Technician
Flushing, New York
Anthony Default
 

I mean if you can’t move the wastegate with vacuum applied directly to the actuator via hand pump you have your culprit

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John Owner
Petal, Mississippi
John Default
 

This vehicle uses pressure from throttle body inlet to Soleniod on front of the motor computer commands it And allows pressure to push wastegate open I had one a few weeks ago the Soleniod was bad bought new one from dealer it was bad took car to dealer said I put a after market Soleniod on it bought it from there parts department they replaced it free car was fixed

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Anthony Technician
Flushing, New York
Anthony Default
 

It does not use pressure to open the wastegate. Wastegate is naturally open and vacuum line from vac pump goes to wastegate solenoid and from solenoid to wastegate actuator; pulling wastegate closed when boost is desired. Naturally open gate is a fail safe as you don’t want wastegate failing in closed position causing overboost.

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William Owner/Technician
San Francisco, California
William Default
 

It defintely uses vacuum to close the wastegate. The wastegate diaphragm is bad because when i pull the wastegate a little to the close position it does not hold vacuum. Dealer said the wastegate only comes with the $4000 turbo.

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Anthony Technician
Flushing, New York
Anthony Default
 

I just did a turbo on a 16 c300 for same issue. Warranty company decided to send us a lkq turbo instead of us getting a new oem turbo. It worked but wouldn’t have been my choice.

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William Owner/Technician
San Francisco, California
William Default
 

Unfortunately thats probably going to be my route too, with zero warranty.

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William Owner/Technician
San Francisco, California
William Resolution
 

Used turbo fixed it. Wastgate diaphragm was worn, would only hold 5 inhg which was not enough to close the wastegate.

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