2006 Chev Silverado

[harvey lee]

Was driving home last week pulling the boat and the tranny slipped a bit. Seemed like it was hot and slipped. I put the transfer case in 4 auto and now it runs fine.

After it slipped and went like into neutral, I checked the tranny fluid and it did seem a bit hot but was still a nice looking red and did not smell burnt.

Yesterday I was driving in overdrive and it slipped again not towing anything. Put it in 4 auto or I can put it in 4 wheel drive and it works fine and shifts fine.

This morning, I went to go to coffe and the truck sat all night, I had to put it in 4 auto to go, regular drive would not work, few minutes ago, now it works. Seem's it works at times and then others I have to use 4 auto.

What is my issue, a tranny or something else? Seem's like if I drive a very long distance it will do this and when it slips, I can shift to parked and it will make a small grinding noise. Put it in 4 auto and all is again fine.

Tranny does have 214,000 miles on it, wondering if a simple fluid and filter change could maybe cure this issue.

Can the tranny work fine when in 4 auto but not in overdrive? I thought if the tranny was out, one could not move it but not true in this case.

[Matt C]

Sounds electronic Tom. If the transmission was going, you loose gears instead of what you described. Especially since it works just fine when you hit auto or full time 4wd.

[harvey lee]

Talked to a guy who does repairs for me and he said it could be the dash pushbutton selector, the shift module or the module on the transfer case. I have 1 of the pushbutton selectors for the dash as I had an issue about 3 years ago and they thought that was the issue so I bought a new one and it was the unit on the transfer case that was the issue. So, I am going to put the new pushbutton selector in and see what happen's, if not the issue, on to one of the others.

I am going to bet it is the shift module inside the truck on the paseenger side down along the bottom side by the door, we'll see.

Hoping it is the pushbutton one as I already have that piece but murphy's law says it will not be.

[harvey lee]

Tried the other pushbutton selector and that was not it. Time to see if the truck set a code.

[Capt. H (Ret.)]

Take it to a certified GM service center and I'll but they can tell you what the problem is. They've probably seen this situation before.

[harvey lee]

Yes, that's the next step.

Had a buddy that has a shop check the truck for codes and no tcm code or no code also for the transfer case. I know the pushbutton selector is good also. Last 2 days, working as it is suppose to. I was hoping it would have set a code, easy then but nope.

Did read online through a GM forum online that on very damp days, the wires can also cause this issue but that is rare.

Hate going the route of a GM dealer as their costs are so high compared to many others for their shop rate but I guess I have no other choice at this point. If I could figure out what elec part is the issue, I could fix that myself but I need to figure that out first.

[CaptainMusky]

Interested to see what you find out, but the tranny wouldnt seem to be the problem IMO. Switching to auto 4 wouldnt have anything to do with the tranny so this seems a bit odd.

Is it "slipping" at any certain speeds? Start out from stop or in between shifts? I am wondering if its possible the shift mechanisms are somehow getting stuck between drive and neutral or something. Perhaps that needs adjusting, not sure if its even possible with everything electronic these days.

[delcecchi]

How much for the other two parts? Is there a test procedure?

[harvey lee]

Yes Del, the 2 other potential issues should set a code so I have been told. I had that check and no codes. I read online that if you have a issue with the transmission control module it should set a code. The other part on the transfer case was replaced about 2 years ago but that was for another issue, the truck would not shift from 4 to 2 wheel drive and that part cured that issue. That part also should set a code. The only other thing I can figure out from my research is that the wiring harness from the pushbutton control on the dash to the tcm could have a bad or intermitent wire connection issue.

I believe there is one other part that is connected with this elec shfting issue but have not learned much on that yet, Still digging into it.

I believe both the other parts are around the $150 mark for one and a few hundred for the other. I have thought about buying the 2 other parts but if it is the wiring harness, then I just wassted $2oo plus dollars.

I could replace the one on the transfer case but I would still have to have a GM dealer set the code for that part.

I just keep researching online and I have seen many issues with this year truck and the driveline but not one shown with the issues I have.

Sooner or later I will get this figured out, I guess a process of trying or testing everything as something has to show up defective. if it is the wiring harness, I guess when it works, hard to find it.

[harvey lee]

Interested to see what you find out, but the tranny wouldnt seem to be the problem IMO. Switching to auto 4 wouldnt have anything to do with the tranny so this seems a bit odd.

Is it "slipping" at any certain speeds? Start out from stop or in between shifts? I am wondering if its possible the shift mechanisms are somehow getting stuck between drive and neutral or something. Perhaps that needs adjusting, not sure if its even possible with everything electronic these days.

No slipping and it shifts fine and at the recommended rpm's. The issue is, while driving in 2 wheel drive, it can and will but who knows when while you are driving, when you let up on the gas, it will go into neutral, then nothing. Then I can hit the 4 auto button and all is good. 10 minutes later, I can go back to 2 wheel and it will work for maybe 10 minutes or two days, who knows.

I can start the truck up after sitting all night and it may work in 2 wheel or may not, then it sounds like it is trying to shift into drive but will not. Then go to 4 auto and all is fine again. if you are in 2 wheel and have the tow haul on, then all is fine also.

You never know when it may or may not jump out of drive but it will after so long. Thenh it ma6y go right back into drive in 2 wheel without hitting the 4 auto or 4 hi or 4 low.

I have been told by 4 shops that it has to be an elec issue so that is where I am research. The tranny shifts fine, makes no noise and yes, the fluid is at the correct level.

[delcecchi]

Not being a mechanic, I was wondering if it is cheaper to pay the diagnostic charge or to easter egg the problem.

[harvey lee]

I would agree and I may end up at the GM dealer. I just figured I could figure this issue out without going to a dealer. MOst times I can find the issues and fix them myself but when you do not have the tools or test equip to diagnos the problem, it gets hard for a shade tree mech.

Maybe not, so far it has cost me nothing and I have elimanated a few things.

[harvey lee]

Well, I went up to the GM shop and they asked me what it was doing and asked it if set any codes. I explained what it did and said no codes and no transfer case code. Also said I had a good pushbutton switch for the dash, tried that and that made no difference. They kknew that they had replaced the part on the transfer case a few years back but off course that could have gone bad.

They simply had no idea what could cause this issue.

The tranny guy and the service manager said they were going to check for any service bulletions and also call GM to see what they think it could be.

Both were lost as to what it could be, had never heard of an issue like this.

I am hopeful that GM will have some idea what the issue is.

[Scott K]

I am not familiar to how GM shift patterns work, but if it sometimes slips, and to stop it from slipping you can either put it into 4x4(*AUTO), or engage the Tow Haul switch, I would be curious as to whether GM bumps line pressure in 4x4, to firm shifts to spin 4 tires? Because I know on Fords they bump up line pressure in Tow Haul mode. If they do bump up line pressures, I would be suspecting a small leak in a seal internal to your transmission, that by the extra boost in line pressure it is enough to make the clutch engage.

If the transmission were actually slipping, it should set a code. Other then that, I dont see any correlation between the tow haul switch, and the 4x4.

If I were diagnosing this, I would first start with seeing what the epc is being commanded at in 2HI, and 4Auto, and again with the tow haul engaged. I would then hook a line pressure gage up to the transmission to see what the line pressure is doing.

The other option is to see what the encoder motor is doing when it is slipping. You could also unplug the encoder motor, and when it slips, put it in 4 auto again, and see if it still causes it to stop slipping. If it does, you will know it isnt in the transfercase, then you know it is the command of the 4Auto causing the slip to stop.

[Macgyver55]

Harvey I had one years back that acted similarly and it turned out to be a broken snap ring in the transfer case. It was allowing the gear to "walk" on the output shaft and so sometimes it would stay in place and work and other times it would slide out of place and free wheel (in 2wd) but always worked in 4wd. It was a fairly easy fix and relatively inexpensive if that is the problem.

[harvey lee]

Yes, I googled Silverado transfer case and found numerous owners that have had the exact same issues so I am sure it is in my transfer case or some elec switch going to it.

More research should give me some more direction.

Hoping the GM dealership will call me with an answer from GM on what they believe is the issue.

I would rather not take it to a dealer and let them start to look at this and that without having a very good idea of what to replace or what the possible issue could be.

Not interested in spending $100 an hour for a research project.

I would think between the dealer and GM, they could get close on what the issue is. I am now sure it is transfer case related.

[harvey lee]

Well after going to the local GM shop and they could tell me nothing, said they would call GM and see if they could figure out what the issue is with nothing there either.

Buddy of mine that was trying to figure it out called me today and asked if I could bring the truck to him.

Got there, he checked for codes and nothing even though 3 times while driving the truck did set a code as it said service 4wd on the dash.

Today he hooked up his code finder, started the truck and no code. Then I tried to shift drives with the push button and it set the code while hooked up to the code finder.

Result, a encoder chip for the inside of the encoder which tells the transfer case when to shift.

I was really surprised that it would set a code but it had to happen at the time the code reader was hooked up.

Bout a $90 part and a hour labor.

Glad he finally figured it out as GM was of no help at all.

Glad we figured out the issue without having someone go on a hunt for what was wrong and buying unneeded parts, been there and done that before.