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2005 sierra 4x4. 4 wheel low will not engage. Sounds like my hubs are trying to lock then kicks back into 2wd. 4 hi does work.And if I run my truck in 2wd sometimes truck will kick into neutral (like transmission just went out). If I run in auto 4x4 problem doesn't occur. Does this sound like encoder motor on side of transfer case or front axle actuator? Front axle actuator has already been replaced once. I was thinking it's the front axle actuator but the kicking trans into neutral threw me for a loop UNLESS the front actuator is trying to go in 4 lo and kicking the transfer case into neutral while I'm driving. Any thoughts will greatly be appreciated. Next step would be the dealership but I hate spending that type of money.

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you're jumping to conclusions about what you think is happening ,,,,,,stop that ,,,have it scanned ,,,thats the first thing to do ,,,then leave it with the tech/shop to diagnose it ,,,,,unless ya want to remove it and tear it down yourself

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Thanks for the reply. Fixing it doesn't bother me and I work in a maintenance shop but it's diesel mechanic work. I've made an appointment to have it scanned so I'm not replacing what doesn't need to be and get it over with and running right. Was just trying to do some backyard troubleshooting lol.

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  • 2 weeks later...

My 2006 Z71 is doing the same thing plus it is going into neutral on its own when in 2wd. That's quite a surprise at 70 mph and on cruise control. The truck slows down, the engine revs up and you have to cut the cruise manually by turning the switch on the turn signal stalk to the off position. I thought it might be the encoder motor but don't have the knowledge so it's in the shop.

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Just talked to a gm tech at the dealership he's their 4x4 guru and 1 of my friends friends lol. But it isn't that hard to do yourself don't even have to fully remove the front driveshaft and it's 3 bolts and unplug the harness. I got the encoder motor for 183 from gmc and if the did it I would've had a $800 bill. Doesn't take but 30-45 mins. But he told me to make sure to cycle the 4 wheel drive at least once a month or it would do it again bc the encoder motor would lock up. And he also said to remeber to back up the truck 15 feet after it was put it 4 wheel like the old days. He said even though it's push button still need to do it so it'll fully disengage. It may be overkill but I'm taking no chances.

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Backing up 15 feet to disengage 4WD is 50000000000% BS. That may have applied to the crappy electronic hubs of the 80s and 90s on some trucks but GM has to the best of my knowledge never used those. That was a Ford thing with the junk they used up to 96-97. Encoder motors fail. Your truck is 9 years old. It may happen. Cycling 4WD monthly isn't a horrible idea but backing up won't do anything but use a bit more fuel. :lol:

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The way he put it to me was the spring in the encoder motor is like a spring in a magazine. In other words if left in 1 position under pressure the spring will weaken and not function properly.

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The way he put it to me was the spring in the encoder motor is like a spring in a magazine. In other words if left in 1 position under pressure the spring will weaken and not function properly.

He's wrong. Springs get weak from cycling, not from staying in one position.
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Ok I understand both of yall. But also makes sense in a way. If I leave bullets in a magazine for let's say a year the spring in the mag will not function properly and cause a stovepipe. What he was telling me was to cycle thru 4 wheel drive so the spring can function the way it's supposed to instead of being in 1 position under tension. When Broke down in those terms it makes a Lil sense. But the guy that told me that works at my local gmc dealership and is also the 4 wheel drive guy that all the mud trucks down here use. But yes yall have valid points. Cycling a spring will make weak. And not staying in 1 position will not lock up. Maybe I said it wrong but I was breaking it down to simple terms. I'll go further this time. Leaving a spring in 1 position under a load or compressed it will lose its springy Ness. Leaving it in 1 position is also not what it was designed for. Now yes cycling will make a spring weaker but it's functioning like it's supposed to. Compressed then relaxed. And sitting in a compressed position over time the spring will not function fully if kept in a compressed position. Same way with valve springs if left with pressure over a period of time the spring will not go back to the orginal height. That's why it makes some sense to me.

Now yall have the gm experience I guess BUT my experience with springs comes from 23 years of racing experience and motor work. I also ran in the nascar Whelen series and if u choose not to believe anything about the spring ask any engine builder why they change springs in a motor that has been. Now this sounds like a passing match and I do believe I just made it over the fence lol.

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Yes I put the encoder motor on but it wouldnt switch out of neutral on the transfer case til I shifted the truck into neutral. It works great now. Now up until this point my truck has only been in 4x4 in 5 years. But it cycles thru 4 hi 4 lo and 2wd. And it doesn't clunk as loud when the front locks in 4lo

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  • 4 weeks later...

Well here is the result of my trip to AAMCO. I took the truck in told them I thought it was the encoder motor but asked them to drive it and see what they thought. Their guy said it was a split ring in the carrier assembly in the transfer case and needed to put the "updated" ring in. $1000 later - it was the encoder motor like I told them in the first place. So much for the "experts" at Double A- beep beep- MCO. Shame on me for second guessing myself and my research. I bought the encoder motor from Rock Auto for $167 and "the experts" put it in- yes they charged me. Just shoot me!!!!!!

 

Now there is what appears to be a 1/4 diameter vacuum hose hanging down on the right side of the transmission. It looks like it goes up to something under the hood near the back side of the engine. Anyone have any ideas? I'd take it back to " the experts" but I'm afraid they would tell me some tall tale - and then charge me for another

misdiagnosis.

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After several years of fighting this problem. I finally changed out the "Encoder Motor Sensor". Finally decided to do it when my "SERVICE 4WD" came on each time I started up and my lights on my control were not on, for a month. I also went through the shift in to neutral at highway speeds as well, never fun! Just wait until your in 4L when you start up and you have to disconnect the battery and wait an hour to get it out, that's a ton of fun on a cold winter morning. By the way, I'd like to know just how you got the encoder motor out without removing the front drive shaft.....

After putting it in, everthing seems to work just fine, cyles between 2H, 4H and Auto as it should, goes in to 4L when in neutral as it should. no more warning indicators.

However, it won't shift the transfer case in to nuetral. Is there some kind of reprogramming that needs to be done?

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