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Discussion Starter #1
Okay. This has been going on for over a month. The dealer has had my 2018 GMC Terrain Diesel twice for over 30 days total. Back before Christmas, I took my Terrain in because the "DIC" showed a display that read:
SERVICE
EMISSION SYSTEM
SEE OWNERS MANUAL NOW
175 MILES UNTIL 65 MPH
MAX SPEED

At the same time another DIC message came on and said "Engine Power is Reduced". And my speed dropped down to 20 MPH. The dealer quickly came back and said that the intake inlet tube was defective and needed replacing, $555 cost. Because of the GM strike a while back, the part was on back order. I was skeptical that that was the problem. Okay, the strike was a big part of them having the car so long. I get the car back and within 100 miles, the same exact thing happens again to the car. I take the car back to the dealer, and they cannot duplicate the problem, but keep the car a week. Yesterday I get the car back, and the car again does the same thing, DIC messages and reduced power. All this happened after driving only 110 miles. The car is very dangerous when the power is suddenly reduced. I love this car for its power and gas milage, but it is now very unreliable. I could find nothing in the Owner's Manual that was helpful. Has anyone had the same experience?????
 

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I know that the diesel owners won't want to hear this, but with the number of reported problems with the diesels vs the gas engines in the 18-20s, it seems like the diesel was not quite ready for prime time when it was released.
 

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Did the dealer force the DPF regeneration?

This is what i was going to ask...also is this vehicle affected by the reprogramming recall that kind of fixed some issues with the automatic regens.
This does look like the system believes that the DPF is filled up ...either you are not putting enough highway miles on it for automatic regens or the sensor for DPF pressure is bad.
 

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Discussion Starter #5
I put the OBDII scanner on the car yesterday and got a CODE: P0046 (Turbo Super Boost Control Solenoid CKT Range / Perf. I changed the air filter and inspected the work they say they performed. I can honestly say I don't think they changed the inlet tube on the intake. It is dirty and nasty like the rest of the engine. I even had to pop it loose. I'm not sure where to go from here. The engine light on the dash will not go away, and I cannot seem to cancel it. Help would be appreciated!
 

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Discussion Starter #6
DPF Regen. I really don't know anything about that stuff? If I know what the specific questions to ask are, I will be happy to take it in and ask them? I put tons of HWY miles on the car. Every other day I put about 80 HWY miles on it at a time. Car has 61K on it now.So I'm averaging 30k plus a year. I asked about the recalls, they said they have been performed. Thank you for the help!
 

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Discussion Starter #7
Found this today:
P0046 code definition

Turbo/Super Charger Boost Control Solenoid Circuit Range/Performance
What the P0046 code means

This code has varied definitions as provided by the manufacturer. Generally, the Engine Control Unit (ECU) has detected an out of range reading in the turbocharger or supercharger boost control circuit. This code is related to circuit A and an area of the system circuit, as opposed to a particular malfunction or component.
What causes the P0046 code?


  • Vacuum leaks on the intake manifold
  • A dirty, restrictive air cleaner
  • The waste gate is either stuck open or closed
  • A plugged or leaking intercooler
  • Loose connections or a bad gasket between the exhaust manifold and the turbocharger
  • Loose connection between the turbocharger and the inlet pipe
  • A bad boost sensor
  • Shorted or open wiring in the boost sensor circuit
  • Loose, corroded, or disconnected electrical connectors in the boost sensor's 5-volt reference circuit
  • Turbo failure from internal oil leaks and oil supply problems, causing bearing failure and blade damage
What are some of the symptoms of P0046 code?


  • Low or no boost and a loss of power during acceleration (most common)
  • Engine boost will be zero and the engine will have no boost
  • The engine will idle normal; only acceleration will be affected
  • The Check Engine Light would then come on once the ECM has seen that the solenoid circuit has gone out of specifications
How does a mechanic diagnose the P0046 code?

The code is normally preceded by the Check Engine Light coming on the dash. The mechanic must use an OBD-II scanner to identify the code, then reset the code and test the vehicle to see if the code returns.
If the P0046 code returns, then the mechanic should follow the test procedure:

  • Inspect the turbo or super charger system for loose connections, including hoses and lines being cracked or damaged.
  • Inspect the wiring on the boost sensor and related wiring for loose connections, damaged wiring, or faulty sensor.
 

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This looks like good information to look at what could be wrong....
follow the pipe out of the turbo into the intercooler and out of it into the engine...see if there are breaks or the tube popped out etc...if you can remove the inlet or outlet of intercooler...see if oil is trapped there...Some turbos sometimes for some reason, i never understood, pushes oil out that way.



you may be out of the b2b warranty but you are still covered by some emission warranties which i think expire at 70K miles and 80K miles...which warranty for which part i am not sure....so some of the sensors might be covered still and definitely a damaged DPF is still under warranty i suspect.
 

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Discussion Starter #9
Okay. I am able to duplicate the failure. 3 times I have been able to repeat this.

I drive the car on the hwy about 40 miles between 70-80mph. When I get to my destination I do about 20 minutes of small town driving. Then I return the 40 miles at about the same 70-80mph and exit the HWY. I stop at three traffic light for a minute or so each. They are about a mile from each other. On the third light, as I leave the intersection, the Emission warning comes on and the power is now reduced. This goes on until I pull over and turn off the car. I wait only about 10 seconds before I start the car. The emission warn is still on, BUT the power is not reduced and I can drive at normal speeds again. Unfortunately, I only have a few miles to drive before I'm home, so I have no idea how long before the power is reduced again. Does this help anyone? I want to give the dealer, whom I feel has never seen a diesel Terrain before!!!!!
 

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if the dealership does not have experience in recent diesels take it to any other GM dealership that have a larger volume servicing small diesel trucks etc....remember it does not need to be a GMC dealership ...it could be a chevrolet one too.
The CEL is pointing to either bad sensor on the airpath or real blockage to the air path...there is no wastegate on this engine it has a variable geometry turbo.
 

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Discussion Starter #11
I went back to the dealer yesterday. Explained what I had learned form the forum. Their main technician thinks it is actually something to do with the DEF pump, and says he has seen this once before. Unfortunately, the guy is so busy that they can't even get to it for a week or two. Any thoughts?
 

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Discussion Starter #12
The dealer is now telling me that there is a leak in the turbo, and the turbo needs replacing. So now they are in search of the part and will let me know when they get it fixed. GM has said that the turbo is covered under the power terrain warranty. So it won't cost me this time. I've been without my car a total of almost two months now. I hope this fixes the problem. I will keep you posted. I have 61K miles on my 2018 Terrain Diesel.
 
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