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  1. #1
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    Default 4-wheel drive Problem, GMC Sonoma (Car guys?)

    We have a 2002 GMC Sonoma Extended cab that we bought used in 2008 to tow our boat. It does a great job towing, but the damn thing has had a ton of things go wrong with it. The most annoying one is a recurring issue with the 4-wheel drive. It has a push-button selector in the cab and it will not shift into 4HI. It doesn't even "try". You can get it into 4LO if you put in it neutral and then shift to park while the lights are blinking, but 4HI just does not work.

    We've had it fixed three times, twice at one mechanic and the third time at another, and all three times they said it was an issue with a vacuum line. All three times it failed to work again after a few months. We had another mechanic tell us that the motor in the transfer case will get gummed up if you don't use it enough. I don't know it that makes sense, but the truck did sit more than it was driven until I got my license last year (I'm 17). I did some research and I guess the most common problems are the solenoid freezing up that actuates the vacuum or the vacuum line having a hole burned through it by the exhaust. I would guess, based on having no response from the status lights, that the solenoid is frozen. Anyone have any better ideas or know how to fix that problem?

    This is a big issue now because we got an inch of snow last night and I had absolutely no traction on my unplowed side-street this morning trying to get to school. I had to put it in 4LO and go 10MPH to get out.
    2004 Wellcraft 180 Sportsman w/ 115 Yamaha 4-stroke.

  2. #2
    Commander MTboatguy's Avatar
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Warn used to sell replacement solenoids for these that fixed the problem, I had to buy one, I also used braided coverings on all of my vacuum lines to avoid the exhaust problems with melting the lines. There have also been companies over the years, that sold replacement electric systems to replace the vacuum systems in the GM rigs.

  3. #3
    Master Chief Petty Officer royal0014's Avatar
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Sounds like an issue with the shift motor more than vac. lines.




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    Commander MTboatguy's Avatar
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Quote Originally Posted by royal0014 View Post
    Sounds like an issue with the shift motor more than vac. lines.




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    Same thing I thought when it first happened on the one I had, but low and behold, it was melted vacuum lines, seems to be a very common problem on many GM 4x4 vehicles, which is why the aftermarket companies have made solutions for it.

    One other thing, I forgot to mention, you need to check the vacuum valve that is located on the wheel well under the hood, there is a vacuum line that goes in one side and a cable that goes out the other side, the vacuum closes the valve and the closing of the valve pulls on the cable that pulls the gear into the 4wd position, the older the valve the more likely it is to have a pin hole in it, that will not allow the vacuum pressure to close it. I have had that happen as well, I replaced it with an electric switch kit from one of the companies, which replaced the vacuum valve, when you activated the 4x4, the electric solenoid pulled on the cable.

  5. #5
    Master Chief Petty Officer royal0014's Avatar
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Quote Originally Posted by MTboatguy View Post
    Same thing I thought when it first happened on the one I had, but low and behold, it was melted vacuum lines, seems to be a very common problem on many GM 4x4 vehicles, which is why the aftermarket companies have made solutions for it.

    One other thing, I forgot to mention, you need to check the vacuum valve that is located on the wheel well under the hood, there is a vacuum line that goes in one side and a cable that goes out the other side, the vacuum closes the valve and the closing of the valve pulls on the cable that pulls the gear into the 4wd position, the older the valve the more likely it is to have a pin hole in it, that will not allow the vacuum pressure to close it. I have had that happen as well, I replaced it with an electric switch kit from one of the companies, which replaced the vacuum valve, when you activated the 4x4, the electric solenoid pulled on the cable.

    Just to clarify, the vacuum 'valve' is under the battery tray. It pulls a cable which engages the front differential. Often the cable gets corroded by battery acid and ceases to function. And a hole in the vac will do the same thing.

    The reason I did not think this was the problem is because the OP says the truck will shift into 4Lo but not 4Hi.
    Could be vac lines, I'll admit. But if it was the vac 'n' cable for the front diff. it wouldn't shift into 4-wheel-anything.

    Also, if your mechanic crossed up lines at the tranny, then the vacuum solenoid can fill up with ATF. Don't ask how I know this Gotta love BIL's



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  6. #6
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Ok so I know my way around my boat, but I haven't really worked on cars. Can I test the function of the vacuum lines myself or would I be able to see where the exhaust has melted them? How hard is it to access that vacuum valve and can I test the function of that? Or should we just take it to a mechanic and have them install the aftermarket parts?

    But just for clarification (I'm probably completely wrong), there is a vacuum line originating from the engine (I assume) that sits too close to one of the exhaust manifolds and then into the valve under the battery box. When I hit one of the 4 wheel drive buttons, that valve opens and allow the vacuum to pull on a cable which then goes to the transfer case and signals the motor to change the gears.

    Sure seems like a run around way of doing it, why can't a signal be sent from the buttons straight to the shift motor? What happens when I tell it to go back into RWD?
    2004 Wellcraft 180 Sportsman w/ 115 Yamaha 4-stroke.

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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Actually, on mine there was three vacuum lines, one for input, one for 4 hi and one for 4 low, I had a hole in the 4 hi line, but could still shift into 4 low..

    When you tell it to go to RWD it stops the vacuum and the valve relaxes and shifts it out of 4WD. I was much happier after I replaced mine with an aftermarket system, never had a failure after that. Where I live, 4 WD is a matter of life and death!

  8. #8
    Master Chief Petty Officer royal0014's Avatar
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Quote Originally Posted by Flynny View Post
    Ok so I know my way around my boat, but I haven't really worked on cars. Can I test the function of the vacuum lines myself or would I be able to see where the exhaust has melted them? How hard is it to access that vacuum valve and can I test the function of that? Or should we just take it to a mechanic and have them install the aftermarket parts?

    But just for clarification (I'm probably completely wrong), there is a vacuum line originating from the engine (I assume) that sits too close to one of the exhaust manifolds and then into the valve under the battery box. When I hit one of the 4 wheel drive buttons, that valve opens and allow the vacuum to pull on a cable which then goes to the transfer case and signals the motor to change the gears.

    Sure seems like a run around way of doing it, why can't a signal be sent from the buttons straight to the shift motor? What happens when I tell it to go back into RWD?

    Ok, the valve under the battery only operates the cable which engages the front diff. There is only one vac line to it. Pull the battery and there are two bolts towards the front that hold the batt. tray in place. The valve is on a bracket and looks simular to the one that operates cruise control. Suck on the hole in the back and the bellow should collapse

    There are aftermarkets to replace the vac with a cable to the cab of the truck, but you still need the button for the transfer case, and it still uses the original cable! On my '95 I determined it to be cheaper and easier to keep it all factory.

    The shift motor at the transfer case is a whole other operation. I always assumed it works electrically, never had problems with that area ..... Maybe your '02 is different.

    I've told you enough to be dangerous. Get a Haynes or Chilton, it'll tell you the specifics to replace parts. That cable has a trick to it.

    Good Luck Figure this was of no help



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  9. #9
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    This post is a little confusing ..can you clear it up
    Your switch lights {dash** work all the time
    or just intermitaly
    if sometimes check your electrical connectors
    From what I read low lights but high doesn't
    or nothing lights
    Does your heater vent control work right?
    Sounds like mutiple problems rather than one
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  10. #10
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Quote Originally Posted by dolluper View Post
    This post is a little confusing ..can you clear it up
    Your switch lights {dash** work all the time
    or just intermitaly
    if sometimes check your electrical connectors
    From what I read low lights but high doesn't
    or nothing lights
    Does your heater vent control work right?
    Sounds like mutiple problems rather than one
    How the heck did you know? But I'll get to that in a second...

    Sorry for the confusion. What I meant is if it's in RWD, the light for 2WD is on and works fine. If I press the 4HI button, there are no sounds, no blinking lights, just no response at all. If I press the 4LO button, both the 4HI and 4 LO lights flash until I shift into neutral, and then park. Then it clunks into 4LO and the 4LO light stays on. Then I can shift into drive to drive in 4LO. To go back to RWD, I just press the 2WD button in neutral and it shifts back quickly.

    As far as the heater vents, the floor vents will not work, if I set it to floor the air just comes out of the windshield vent. But I don't know if that's related because that only started happening a month ago and this 4 wheel drive problem has been happening for over a year and a half.
    2004 Wellcraft 180 Sportsman w/ 115 Yamaha 4-stroke.

  11. #11
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Your not shifting into 4 LO while the vehicle is moving are you? The shift on the fly only applies to 4 Hi, I have seen transfer cases blown up, trying to shift into 4 LO while the vehicle is moving.. Now something may be different on yours, but that is how it has always worked on my various 4WD vehicles.

  12. #12
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    I don't think he's shifting into 4WL on the fly, putting the tranny into Park while moving will blow up more than just a transfer case. dolluper asking about the heater was a very educated point. Vacuum is used for heater controls and front axle control. He is probably about to come back saying you have a vacuum leak and to check all the vacuum line. I would suggest that.
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  13. #13
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Quote Originally Posted by GA_Boater View Post
    I don't think he's shifting into 4WL on the fly, putting the tranny into Park while moving will blow up more than just a transfer case. dolluper asking about the heater was a very educated point. Vacuum is used for heater controls and front axle control. He is probably about to come back saying you have a vacuum leak and to check all the vacuum line. I would suggest that.
    Ah I love learning new stuff. That's really interesting. It makes sense now that the air doors are controlled by vacuum based on the sound they make. But again, maybe that's a new vacuum leak that's unrelated to the 4 wheel drive. Hopefully tomorrow I'm gonna get under the battery box so I can see exactly what you guys are talking about.

    As for shifting I'm the fly into 4L, I am not. Usually I'm not moving, but I've tried rolling forward at 2-3MPH as the manual suggests. Of course I stop completely before I shift into park.
    2004 Wellcraft 180 Sportsman w/ 115 Yamaha 4-stroke.

  14. #14
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    Shifting into low will rule out the heater control vac problem...if it didn't shift into low it would
    be the cause....you have no lights for high so you have an electrical problem
    between the switch {dash** and the actuator.. or bad ground or actuator or switch
    check all your fuses...to be sure // high vac line could be leaking also....battery box under
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  15. #15
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    Default Re: 4-wheel drive Problem, GMC Sonoma (Car guys?)

    If I remember correctly and it has been a while since I owned one, the heater was controlled by a vacuum ball, which was a different system than the 4wd drive system. I have had the vacuum ball crack, which caused the heater doors to be inoperative.

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