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Chevrolet Tahoe Suburban 4 Wheel Drive Indicator Lights



  • niktnikt Posts: 24
    After replacing the Transfer Case fuse (See my message #25), my 4WD worked OK for a while, but yesterday the fuse blew again and I now believe I have to replace the shifter motor. The local Chev dealer parts manager says the required motor is GM P/N 12386247 for $497.00! I did some digging and found a Dorman (new, not rebuilt) shift motor, Dorman P/N 600-902 that is supposed to be an exact replacement, and which costs $136.99 at RockAuto.

    Am I on the right track here? If not, any other suggestions?

    Has anyone out there made this repair? Is Dorman a reliable product?

  • Hi Nikt,
    Looks like I have a similar problem with my wife's 1997 Tahoe as you are having. She shifted to 4WD the other day and now the thing is stuck in 4wd. Thanks to you I went right to the proper fuse and checked it - it was good. But I have a couple of questions about your entry #25, if you'd be so kind as to answer them. First; Why did you remove the Accessory Light fuse (#3) as well? Was that part of the reset procedure? Second has to do with switching the ignition On and Off 5 times to clear the codes. Can you tell me where you got that information. I'm asking becasue I couldn't find it on the web, but I may not have structured the search properly? Anyway either it's truly stuck in 4wd or I did something wrong because Nothing I did helped. :surprise:
  • niktnikt Posts: 24
    Hi grenneam,

    I pulled the the ATC and Accessory Light fuses because it was suggested by a Chev/GM mechanic in another forum. To understand what these fuses protected, and before doing any of the things I described, I tried to find schematics for the transmission control system at our local library without success, so I can't tell you what effect pulling the fuse had. That same mechanic suggested turning the ignition on and off 5 times.

    I thought I saved the the web address of that forum, but I couldn't find it in the my "Favorites" list. If I find it, I will let you know. I do recall it was an"Ask the Expert" style forum, and answers were free if were willing to wait a day or two for an answer. However, by paying a small premium you could get a quick return with an answer.

    Do you have any thoughts about, or know of anyone who used a Dorman shifter motor?


  • For Nikt,
    Thanks for your reply. I forgot to pull the #3 fuse - I'll try it again with that out. I'm just getting into this stuff with this vehicle and am looking at replacing the TC motor as well. I really don't know anything about the Dorman Motor - just that it appears more expensive than the Cardone that I'm looking at.
    I feel like I've entered Automotive repair hell. I've got 2 vehicles that won't pass inspection, The Tahoe and my wife's 2001 Sienna. We made an attempt with the Tahoe and found out that not only was it not simple (cheap) to fix the 4WD problem but the MIL indicator was burnt out and it also needs a Cat converter and possibly something else. The Sienna is an even bigger nigthmare in that it too has Cat ConV problems and a bad KnockSensor. The Knock Sensor is about $180 and is located underneath the intake manifold so it'll be at least that much to replace it. The Fun part is that the Cat Conv for the Sienna looks like an Unobtainable part until at least Feb 2010 and cost somewhere between 350 and 1400 dollars depending on where I shop. It's also tucked away in such a manner to prohibit anyone with a blow torch from working their magic. The only saving element is that my State has a kickout clause on inspections that allows a Waiver if you spend > $150 on a vehicle trying to fix it. So that's a temporary solution. This has all happened over the last couple of days, I feel a little shell shocked and am just trying to orient my self with what is going on and who/what to try and fix first.. LOL :sick:
  • OH yeah - I forgot this. In my web searches I found mention that replacing the TC motor might necessitate re-programming the TCM (Transmission Control Module)!! Have you seen anything like that? If you have, do you have any idea as to how that's done, or whether it a big deal or not ? :confuse:
  • I have a 2003 Chevy Suburban 1/2ton. I had it in 4 wheel drive, snowy, slushy, wet and rainy. Driving about 50 the front end made a bunch of clanking noise and grinding. There was nowhere to pull off. I switched it into 2 wheel and was able to pull into a parking lot about 2.5 miles. I put it in park, then back into drive, it clanked once really loudly and then made no more noises until I tied to put it back into 4 wheel drive. Can you help?
  • niktnikt Posts: 24
    Thanks to all of you for your comments. I am just regular Tahoe owner, not a crackerjack mechanic, so I can't answer the questions you folks have. What little I know I learned from reading the Chilton and other shop manuals at our local public library and
    surfing the net to find other Chevy and Tahoe forums.

    I hope there is a guy with experience in these matters to advise us on repair and/or needed reprogramming procedures. I am digging into this as best I can because our local Chevy dealer wants $800 to $900 to replace the shift motor which is out of the question for guy not working a steady job (me). I just want to be sure I'm doing all the right things before I buy a shifter motor and try to install it.

    So once again, if any of you folks out there have replaced the shifter motor (sometimes called the encoder motor ( its GM part number is 12386247) please tell us all about and any problems you encountered.


  • niktnikt Posts: 24
    A note of caution for all to consider-----I mistakenly thought my Tahoe needed an encoder (2WD-4WD shifter) motor, of GM p/n 12386247 or Dorman 600-902. I did more checking (I should have done it first) and looked at the RPO codes on the ID sticker on the glove box door. Turns out that the transfer case RPO is not NP1, but actually NP8. The correct encoder (shift) motor is GM p/n 12474401 that is serviced by Dorman 600-901. The plugs and wiring are different and the units are not interchangeable.

    I'm sure a lot of you already know this stuff, but I confess to being a beginner. Years ago, when I scrounged for boneyard parts, RPOs and such weren't a factor--you just found what fit the car you were fixing. Of course my new questions are: Has anyone had experience installing this shifter motor? Any trick stuff to know about? Does any reprogramming have to be done? Is there a cheaper source for this motor?

    Many thanks to you all and Merry Christmas,

  • Ok I have been watching this thread and here is my problem. After recent snow I put the truck in 4 hi now it won't come out into 2wd. the dash switch clicks 2wd blinks then it goes back to 4hi. If you push 4 auto it will change into it but not 2wd. check 4x4 is on but I scanned it and it shows no codes. I pulled the fuses 2 and 3 waited 30 minutes reinstalled but that didn't do it. before i start throwing parts at it where do I start the switch ? My thinking is the transfer case motor 1st or switch 2nd because when the switch clicks i hear no noise at the transfer case. Any Ideas ?
  • I have a very similar problem with my 97 Tahoe and I've got it in the Shop right now. The guy is supposed to replace a Part on Monday. I'll Let you know how it turns out. The vehicle is stuck in 4 whl Hi and won't go to either 2 whl Hi or 4 Whl LO. I don't have an auto button that I know of. It my wife's truck for pulling a horse trailer so I don't get involved with it much. :blush:
  • niktnikt Posts: 24
    My take on my problems as well as all of yours is that we all need to do more research and need some words of advice from a knowledgeable GM transmission tech.

    Does anyone know of a good manual, say a Chilton or Haynes that focuses on GM 4WDs and transfer cases? I looked in our public library, but came up short. I'm not comfortable changing fuses, etc., when I don't even have a clear understanding of how the transfer case operates and how the shifter motor interfaces with what I am sure are splined shifting collars.

    I suspect many of you are a lot more knowledgeable on how a transfer case functions than I am, and if you can help, please pitch in because I'm sure we could all learn something.

    Thanks and Merry Christmas,

  • kiawahkiawah Posts: 3,666
    You can order a set of factory service manuals for your vehicle. Check the back of the owners manual for the ordering details. They are a HUGE 3 volume set, which goes into intimate detail of everything. I always order a set for every vehicle I have bought. If it saves you one trip to the dealership repair department, it pays for itself.
  • niktnikt Posts: 24
    Hi kiawah,

    Thanks for your courteous and prompt response. I will follow up on your suggestion.

  • I have a Silverado 4WD. The electronic push button will go from blinking to a solid light when pushing either 4 wheel High or 4 wheel Low, but the front wheels don't engage.
    Anyone know whats going on?
  • niktnikt Posts: 24
    Re: notawrenchguy

    Take a look at previous messages. Check the transfer case fuses.

    If the fuse(s) are blown, there is a chance that the shifter motor is shot, and you may need a 4WD/2WD shifter motor, also known as an encoder motor. To correctly identify which one your Siverado uses, be sure to check your serial number/option data plate. Check your owner's manual for its location. Copy down the N-codes to determine which transfer case you have and the shifter motor you might need.

    With the correct n-code, a cooperative GM parts counterman should be able to give you the correct encoder motor P/N.

    Hope this helps.

  • I'm lookink for the (ATC) fuse and am a little confused! I have a 2004 Silverado (electronoic) 4WD. I'm looking for my various 4 WD related fuses in the owners manual and find one labled "TREC" (All-wheel Drive Module) , one marked "4WD" (Four Wheel Drive System, Auxiliary Battery), one marked "B/U LP" (Back-up lamps, Automatic Transmission Shift Lock Control System) , but I'm not finding one marked "ATC" (Automatic transfer Case)
    These include fuse panels in the cab and under the hood.
    Any thoughts or direction??

    I looked at my owners manual
  • Thanks for your reply and suggestions
    I'll check the fuses first and pray, although I've reveiewed some previous messages and just sent out another "question" because I can't find a fuse labeled (ATC) Automatic Transfer Case.
  • 85350x85350x Posts: 2
    i have a 96 suburban. i've read through all the posts and didnt see anything on older suburbans. mine is in 2hi and if i shift to 4hi or 4 lo the indicator lights flash. i can hear the transfer case engage but i dont think the front differential is engaging. I had a 94 suburban and i replaced the differential acctuator and that fixed the problem on it but it had a lever on the floor to engage 4wd. i checked fuses and didnt see one for the t-case in the fuse block under the hood. will look again.
  • niktnikt Posts: 24
    To all,

    Just so you all know, my experiences with 4WD have been limited to my 1999 Tahoe and its particular transmission, 4WD control configuration, and fusing.

    I can't speak with any authority on any other year or model GM product (heck, I can't speak with any authority on my own Tahoe).

    My suggestion would be to check all fuses that seem to relate to the 4WD controls and replace any blown fuses. Then try the system. My Tahoe did have a blown fuse which I replaced, and I did restore 4WD operation. After a week, the fuse again blew. I have ordered a new shift motor from Rock Auto to make a hopefully permanent repair.

    I caution you all to check your option data plate to confirm the transmission option codes to get the correct parts. In my area, a helpful Chevy dealer parts guy gave me the GM p/n for the shift motor for that code.

    I can only say that fuses blow because of excess current and that usually means the encoder (shift) motor is possibly faulty and must be replaced

  • Thnaks for the info.....I've checked all the fuses I could find ( as I mentioned in my message # 49) but didn't find out that were blown????
    Today I'll look around under the truck for loose conections, etc.
  • I looked under the truck yesterday, but didn't see anything that looked wrong (disconnected)
    Today I'll stop by the Chevy dealer (parts dept) to see if I can pick-up any additional info regarding fuses and their location. As I previously stated I only found 3 fuses relating to 4WD system (4WD, TREC, B/U LP) but am still trying to find out whether I actually have a fuse for the ATC or a 4 x 4 Module. For all I know the fuse labeled 4WD could be the ATC (Auto Transfer Case).

    If anyone has any other ideas, please advise.
    Thanks for all the comments and suggestions so far.
  • niktnikt Posts: 24
    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.


  • Good news!
    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.

  • niktnikt Posts: 24
    To notawrenchguy,

    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.

    Good luck,

  • Nikt,

    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)

    Take care.

    I guess I'm now "kind of a wrench guy"
  • 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?
  • niktnikt Posts: 24
    To notawrenchguy:

    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.

  • 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?
  • niktnikt Posts: 24
    To: mwdaniel

    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.

  • 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.
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