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Discussion Starter · #1 ·
2022 RS. When you open any passenger door there is a noise from the rear of the vehicle. It is like a loud buzz or humming noise that lasts about 5 seconds or more. Now this only happens after the vehicle has sat for at least about an hour. In other words it happens immediately. But if you then close the door and open it again it does not happen. You try it again after about 30 or 45 minutes it does not happen. Only after it has sat for over about an hour. It is quite loud. Is this a problem? As it comes from the rear, not the engine compartment that makes it even more unusual.
 

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Discussion Starter · #3 ·
Fuel pump?
I suspected fuel pump except the odd part it is only does it after car sits for LONG period of time. If faulty pump it seems it would happen every time perhaps. I may take to dealer but its a pain since it has to sit so long to be recreated.
 

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I'm pretty sure my wife's TB does it when any door is opened and the sound comes from the area of the fuel tank. I would think that after about an hour the fuel in the line would drain back to the tank and need to be "primed" again. I would think that it does it when a door is opened as it's expecting to be turned on and since these cars don't have an "accessory" setting like older vehicles it uses this to kick off the fuel pump. I could be wrong though, I haven't spent much time looking at the fuel system yet as its so new.
 

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2021 Trailblazer RS FWD, Satin Steel Metallic
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2022 RS. When you open any passenger door there is a noise from the rear of the vehicle. It is like a loud buzz or humming noise that lasts about 5 seconds or more. Now this only happens after the vehicle has sat for at least about an hour. In other words it happens immediately. But if you then close the door and open it again it does not happen. You try it again after about 30 or 45 minutes it does not happen. Only after it has sat for over about an hour. It is quite loud. Is this a problem? As it comes from the rear, not the engine compartment that makes it even more unusual.
My 2021 RS does the same thing. Sounds mechanical. I don't really pay much attention to it. Just assume per other post that it's fuel pump being primed or something similar. Would like to know what it is if anyone else knows.
 

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Discussion Starter · #6 ·
I'm pretty sure my wife's TB does it when any door is opened and the sound comes from the area of the fuel tank. I would think that after about an hour the fuel in the line would drain back to the tank and need to be "primed" again. I would think that it does it when a door is opened as it's expecting to be turned on and since these cars don't have an "accessory" setting like older vehicles it uses this to kick off the fuel pump. I could be wrong though, I haven't spent much time looking at the fuel system yet as its so new.
I was too curious so I went to the dealer (service department). Three different service advisors. I described the "problem". They said "we have had some other trailblazer owners mention the same thing. Not sure what it is." I suggested the fuel pump. They thought possible or also the car's computer booting up. I said but the computer is in the back?? They said there are various "computers" in the car that do different things. LOL. Why didn't they just say, yep they do it and we aren't sure why. When I left they said if something gets worse or breaks that is why you have 3 year warranty :).
 

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Discussion Starter · #7 ·
My 2021 RS does the same thing. Sounds mechanical. I don't really pay much attention to it. Just assume per other post that it's fuel pump being primed or something similar. Would like to know what it is if anyone else knows.
I was too curious so I went to the dealer (service department). Three different service advisors. I described the "problem". They said "we have had some other trailblazer owners mention the same thing. Not sure what it is." I suggested the fuel pump. They thought possible or also the car's computer booting up. I said but the computer is in the back?? They said there are various "computers" in the car that do different things. LOL. Why didn't they just say, yep they do it and we aren't sure why. When I left they said if something gets worse or breaks that is why you have 3 year warranty :).
 

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2021Trailblazer RS AWD Scarlet Red Metallic
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There are 2 fuel pumps in the system. The one you hear prime itself is the electric pump that supplies fuel to the high pressure mechanical pump on the engine. It's a low pressure pump that only primes when the vehicle has sat for a while.
 

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Discussion Starter · #9 ·
There are 2 fuel pumps in the system. The one you hear prime itself is the electric pump that supplies fuel to the high pressure mechanical pump on the engine. It's a low pressure pump that only primes when the vehicle has sat for a while.
Thanks so much for the information. I appreciate your feedback
 

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A better question is why is this the only vehicle that I've ever seen that has an audible fuel pump when you open a door... I'm still scratching my head over this.
 

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Discussion Starter · #11 ·
You know I was thinking the same thing. It seems like a step backward in technology and not a step forward. I suppose there may be some obscure reason such as perhaps it is a 3 cylinger, something to do with being manufactured in Korea (part sourced from there), etc. None of which make sense. Further it is a known characteristic of the trailblazer so why not at least mention it in the owners manual so new buyers don't think it is a problem. I previously had a 018 Equinox. It had a strange noise too. Associated when you turned the car off. For a few seconds you could hear something in the engine hum a while, then click, for about one minute. Dealer said it was "the computer powering down".
 

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A better question is why is this the only vehicle that I've ever seen that has an audible fuel pump when you open a door... I'm still scratching my head over this.
Direct injection and push button start are some reasons. Older MPFI systems primed the fuel system with the key in the run position, but push button start doesn't have that option so priming is done when opening a door. DI also has 2 fuel pumps. The electric fuel pump needs to prime in order to have pressure available for the high pressure mechanical pump found on the engine. Priming before the engine is started makes the engine start easier and faster. DI is also different than MPFI in how it primes the system. MPFI primes the injectors while DI primes the mechical pump and not the injectors. I guess GM engineers figured that if you open a door you're most likely going to drive it, so why not prime the fuel system so it's ready.
 

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My Kia Sorento makes a lot of noises when you turn the engine off. Clicking, whirring, etc. Which all seems normal.
 

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Discussion Starter · #14 ·
Direct injection and push button start are some reasons. Older MPFI systems primed the fuel system with the key in the run position, but push button start doesn't have that option so priming is done when opening a door. DI also has 2 fuel pumps. The electric fuel pump needs to prime in order to have pressure available for the high pressure mechanical pump found on the engine. Priming before the engine is started makes the engine start easier and faster. DI is also different than MPFI in how it primes the system. MPFI primes the injectors while DI primes the mechical pump and not the injectors. I guess GM engineers figured that if you open a door you're most likely going to drive it, so why not prime the fuel system so it's ready.
Interesting. Very. I wondered why my Equinox, which also had push button start, did not do this. But as you explained about DI vs MPFI, et. was interestin.
 

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Interesting. Very. I wondered why my Equinox, which also had push button start, did not do this. But as you explained about DI vs MPFI, et. was interestin.
This is only my 3rd vehicle with DI, so I'm still learning myself. I have almost 30 years working on MPFI, so those systems are easy for me to understand and sevice. With all the focus on electric and hydrogen powered vehicles DI might be the last update for fuel injection.
 
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