Hey Everyone,

I am helping out a sibling who owns a GLS50 that is throwing a CEL with errors: P0299,P1670. Unfortunately I am about 1200 miles from him and the advice from a local mechanic was to trade the vehicle in. I have looked up the codes and it sounds like a bad vacuum line, boost hose or possibly a problem with the waste gate. I know he has a aftermarket piggyback ECU, which maybe contributing to the issue.

My question is, has anyone seen this and if so is there one hose or connection that typically has an issue?

Thank you!

• P0299 – Turbo/Supercharger Underboost
  
  • Means the engine control unit (ECU) detects less boost pressure than expected.
    
  • Common causes:
    
    • Vacuum leaks in lines controlling the wastegate
      
    • Boost leaks in intercooler hoses or charge pipes
      
    • Faulty boost pressure sensor
      
    • Wastegate actuator issues (sticking or weak)
      
    • In rare cases, turbocharger wear/damage
      
• P1670 – Turbocharger/Wastegate Control Fault
  
  • Often linked to communication or control problems between the ECU and the turbo actuator.
    
  • Common causes:
    
    • Defective wastegate actuator or solenoid
      
    • Electrical wiring/connectors to the actuator
      
    • Vacuum supply problems
      

 

When this happened to my GLS 63, I was fortunate to be able to reset it and clear the code with my reader. I was pulling jet skis out of the lake and punched it a bit hard and check engine light came on. Drove it home and no performance issue. Hooked it up to my reader, same code and cleared it out.

A month or two later took the vehicle to tale of the dragon and back, 2k miles and no check engine light.

Hoping someone has tried that already.

 

@pardesi Thanks for the reply. My brother said he clears the code about once a week and it keeps on happening...

 

Sooooo many things. I am going to assume this is a GLS550....if so, what year? How many miles? Any proactive replacement of the MANY "Brittle by 80k/Mi" plastic parts that are on the turbo wastegate systems?

 

@OldManAndHisCar Sorry, its a 2017 with I am going to guess about 120k miles..

To the best of my knowledge none of the plastic piping has been replaced. He has been taking it to a local mechanic who is "a nice guy" but not necessarily a Mercedes guy. I would hope that if it was as obvious as just a piece of cracked plastic he would have caught that, but maybe not... I know on my GLK 250 the hoses too and from the intercooler are prone to leaks because of where they are located and that they rub, does the GLS 550 have a similar issue?

 

Ah...I am intimate with that car. Yes, the plastics LOVE to break. Hell, I broke one in the past month just changing plugs/coils. There is one on the drivers side that is prone to fracture (and quite easy to replace). I have even added silicone cooling lines to ours to resolve the water lines from doing the same cracking fun.

 

@OldManAndHisCar Awesome, I can look at the diagram and walk him through checking that! I am guessing the hose is the pressurized side of the turbo?

 

This could be an easy way...to MAYBE, just maybe resolve the issue.

 

What OldManAndHisCar said. I'm assuming M278? I had a P0299 code that only occurred in cold weather. Ended up replacing the check valve (https://www.ebay.com/itm/395683116959), make sure you pick up extra elbows (https://www.fcpeuro.com/products/mer...rts-1170780481) since the original one will likely be brittle, mine cracked when I tried to remove it. This part is easy to get to, easy to replace, and if it fixes the issue the great. If not... your sibling might have to troubleshoot more. Check the wastegate vacuum lines first, if you apply vacuum to the wastegate controllers you should see the wastegate linkages move. If not there may be a vacuum leak in the tubing or the wastegate actuator diaphragm may be damaged. Upstream from the wastegate acutators and their vacuum lines is the boost control solenoid (sits under the plastic shrouding in the vee of the engine), which I believe receives PWM signal from the ECU to modulate vacuum to the wastegate actuators. This part should be an easy replacement, if necessary.

Complicating things, if the vacuum pump check valve has been broken for some time, is the migration of engine oil from the vacuum pump, through the broken check valve, to the boost control solenoid, to the wastegate actuators:
If this is the case your sibling may have to go to town with a can of canned air to blow oil out of the vacuum lines.

Keep us posted.