Last post on Aug 24, 2013 at 7:44 PM
You are in the Chevrolet Suburban & Tahoe
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Chevrolet Tahoe, Chevrolet Tahoe Limited/Z71, Chevrolet Suburban, SUV
#55 of 120 Tahoe 4WD
Jan 11, 2010 (11:54 pm)
Referring to my previous messages, you may recall that on my 1999 Tahoe, the ATC fuse blew twice. This fuse evidently protects the so-called "encoder motor" that shifts the transfer case from 2 Hi to 4Hi, etc. I concluded that the failure to shift was the fault of this shift motor. I checked the 4 WD option code from the option code plate located in the glove box door, then cross-checked it with a Chevy dealer parts person to determine the GM part number for that option code, then checked the applications listed on the Dorman (aftermarket parts mfr) website to find the Dorman replacement P/N. I then ordered the part from a local car parts store rather than mail order in case the part was faulty, wrong, etc., and could be returned. After all this, the store still ordered the wrong part and it had to be-ordered
A skilled (ASE certified) mechanic installed it for me in about one hour's time and the 4WD system now seems to be functioning correctly. I notice that shifting occurs more quickly.
Check and double check your transfer case option code.
If you do get a part, make sure it's the right one.
Don't substitute a bigger ATC fuse, you could have fire in the wire harness.
My opinion: I avoid using the Automatic 4WD as I think it engages harshly.
So far, so good. Best of luck to you all.
#56 of 120 Re: Silverado 4 WD not engaging
Jan 12, 2010 (4:27 pm)
I purchased a Haynes Repair Manual and a friend of mine ( with wrenching experience) came over on Saturday and we diagnosed the 4WD system from the automatic pushbutton to the Acuator/encoder motor at the transfer case to the front axle shift motor (acuator).
Turns out that it was a bad front axle shift motor which is probably the easiest item on the 4WD system to change out The unit screws right into the axle tube..
Thanks again to all of you who made suggestions and shared their issues.
#57 of 120 Tahoe 4WD
Jan 12, 2010 (5:24 pm)
Good job! Please tell me the title or publication number of the Haynes manual you used.
As my Tahoe ages, it may need more repairs, so a manual will be a big help.
Jan 12, 2010 (5:46 pm)
The Haynes Manual ( # 24066) I bought covers Chevy Silverado, GMC Sieera 1999- 2006. it also covers Suburban, Tahoe, Yukon, Denali, Avalanche, etc
You could probaly check it out on-line or at your local Napa Auto Shop (or similar)
I guess I'm now "kind of a wrench guy"
#59 of 120 Re: Silverado 4 WD not engaging [notawrenchguy]
Feb 04, 2010 (4:46 pm)
I have a problem that consists of the "Service 4WD" message comes on and now the damn thing won't come out of 4LO. I was wondering if there is any way of disconnecting the solenoid/actuator and getting back into 2WD?
#60 of 120 Tahoe 4WD
Feb 04, 2010 (6:11 pm)
Disclaimer: Although I got my Tahoe 4WD working, I am NOT a 4WD drive guru.
But, I do want to help. Based on my experience watching the mechanic install the shift (encoder) motor onto my transfer case, and my taking apart the faulty shift motor unit, here is my take on the shifting process and what I suggest:
The shifter motor bolts onto the transfer case and the actual connection is a short shaft that comes from the transfer case that mates with shifter motor. The shifter motor is controlled by the Transmission Control Module (TCM). when you call for 2WD, 4WD, etc., the TCM tells the shifter motor to rotate that stub shaft to engage couplings, etc. that I imagine control splined shift collars, etc. The TCM does two things: It electrically releases a spring-applied brake and spins the shift motor that turns the stub shaft to the selected function (2WD HI or OR 4wd HI, etc.). A rotary position sensor tells the TCM when the correct function has been selected and the motor stops and the little spring-applied brake holds the shaft in the right place (Drive function).
Now, the new shift motor comes with a plastic tab holding it in Neutral position. The owner's manual tells how to put the transfer case in Neutral so the new shifter motor can be installed, but the mechanic that fixed my Tahoe simply took a wrench and turned the stub shaft until he reached Neutral, and then installed the new shifter motor unit.
I conclude from my experiences noted above, that you could remove the shifter motor, rotate the stub shaft to 2WD HI, and drive away. A BIG CAUTION here though; you must find away to lock the shaft in 2WD HI, because you don't have the little brake in the (now disconnected) shift motor unit to hold the shaft in position. Also, you will have to perform a short driving test to assure that have 2WD. If you are electrically and mechanically handy, or have a friend who is, you might be able to energize the brake and motor from an external 12 Volt source to do the shifting. Just don't energize the motor until you energize the brake to release it.
In short, it is possible to get back to 2WD, but please be careful to lock the shaft.
I hope all this helps.
Best of luck to you and please let us all know how you make out on this fix.
#61 of 120 Re: Tahoe 4WD [nikt]
Feb 08, 2010 (1:37 pm)
I also have a 1999 Tahoe and have trouble getting into 4HI during the big East Coast Blizzard this weekend. It finally went in and now it will not go back to 2HI. When I hit the 2HI button, I can hear the motors underneath making noise and the relays in clicking behind the dash. The 2HI lights flash a few times and simply goes back to 4HI. It will not go into 4LO either. I tried warming the transfer case area and motors with a heat gun, no luck, Pulled the fuses as suggested above, no luck. Went back out after luch and now the lights on the selector are dead; fuses was blown. As soon as I intalled the new fuse it blew.
Just dropped it off at the local Chevy Dealer and I am impatiently waiting for the call. Based on the symptoms read in this thread and what I have described on my Tahoe, does it sound like the motors were locked up and now they just seized, causing the over-current?
#62 of 120 Tahoe 4WD
Feb 09, 2010 (12:20 am)
Speaking not as an expert, it sounds like you diagnosed the problem correctly. I'm guessing the dealer may have to scan the TCC for trouble codes to see what else, if anything, may need repair. Your Tahoe is like my '99 Tahoe, and after 10-11 years, "stuff" just wears out.
Good luck on resolving you 4WD problem.
#63 of 120 Re: Tahoe 4WD [nikt]
Feb 11, 2010 (9:40 am)
Well the dealer told me that they need to replace the encoder module behind the dash, that was going to be approx $700, if that did not solve it, they would have to replace the encoder motor, add another $700. There is no way I could spend that just to have 4wheel drive a few times a year. I had them lock it into 2 hi, they pulled the motor and disconnected the drive shaft, so I now have a 2 wheel drive Tahoe. Set me back a couple hundred dollars.
Thanks to all the thread posting out there.
#64 of 120 Tahoe Dashboard Indicators Failure
Feb 14, 2010 (8:31 pm)
My 2003 Tahoe indicator gages on the dashboard are begining to go out. My mechanic tells me that the resistors are failing, hence the gages going out and sometimes re-setting again. I have heard that this is a more common than not problem with Chevy and GM Trucks. The repair seems to be replacing the dashboard completely - a pretty expensive option.
Any information on if this is happening generally or how it has been handled would be appreciated. Thanks,