2006 Silverado will not go in 4L

[jlr2267]

2006 Crew Z71 with 5.3 and electronic 4WD shift:

 

Tried to shift into 4L per GM manual (in neutral, still and with very slow roll) and it clunks two or three times and shakes the entire truck, but does not engage. Shifting to 4H works fine. After trying a few times I got a “Service 4WD” light.

 

Any ideas on what the problem might be?

 

Things are definitely moving down there, just not locking up!

 

 

[Supreme Pizza]

I would start with checking the transfer case and front differential fluid levels. Couldn't hurt to disconnect the battery for 30 minutes. Try engaging 4L in forward and reverse. Are your front and rear tires the same size, age, tread wear, and tire pressure? 

 

 

A $25 test: 

 

  https://www.amazon.com/JahyShow-Transfer-Selector-Cadillac-Chevrolet/dp/B076BLDTXT/ref=sr_1_12?ie=UTF8&qid=1526073157&sr=8-12&keywords=2006+suburban+4x4+switch

[jlr2267]

I would start with checking the transfer case and front differential fluid levels. Couldn't hurt to disconnect the battery for 30 minutes. Try engaging 4L in forward and reverse. Are your front and rear wheels the same size, age, tread wear, and tire pressure? 

 

 

A $25 test: 

 

  https://www.amazon.com/JahyShow-Transfer-Selector-Cadillac-Chevrolet/dp/B076BLDTXT/ref=sr_1_12?ie=UTF8&qid=1526073157&sr=8-12&keywords=2006+suburban+4x4+switch

 

Tires are all new. Fluid levels are all good. I also tried rolling fwd & backward, no luck.

 

I don’t think it’s an electronic problem...the actuator is definitely moving...it’s just not engaging. I get several mechanical clunks before it gives up.

[Supreme Pizza]

I would order that switch. Also, you could try putting the vehicle up on 4 jack stands to see if it will go in. You may have an encoder motor issue. 

 

https://www.amazon.com/gp/product/B00CD7E248/ref=ox_sc_sfl_title_33?ie=UTF8&psc=1&smid=AYUN1EXO5XQB3

[Supreme Pizza]

I would probably replace the encoder motor or encoder ring sensor. Must verify fitment, and watch the how-to vidya. 

[Supreme Pizza]

If its working in the 4 high range, then the front end can probably be excluded as the issue. That leaves the transfer case. 

 

    Dash switch

    Encoder motor 

    Encoder sensor ring

    Speed sensor issue 

    Transfer case internal problems

    Wiring 

    User error 

 

    Those are the possible causes. 

[jlr2267]

If its working in the 4 high range, then the front end can probably be excluded as the issue. That leaves the transfer case. 

 

    Dash switch

    Encoder motor 

    Encoder sensor ring

    Speed sensor issue 

    Transfer case internal problems

    Wiring 

    User error 

 

    Those are the possible causes. 

 

Ok, had it scanned and it threw codes B0790 and C0035. The C-code is left front wheel speed sensor, no idea what the B-code means.

 

I did notice that I never get a neutral light on the dash switch...even when in neutral it’s always 2H or 4H...

[Supreme Pizza]

To clarify, your "neutral" light for the transfer case has nothing to do with your transmission gear shifter selection. You have two neutral sections: transfer case and transmission. To select neutral on your transfer case, you need to hold down 2 transfer case shift buttons. For the transmission, you shift to N. 

[Supreme Pizza]

I'm no expert on wheel speed sensors, but I do know that the transfer case will not shift in to 4 low unless the wheel speed sensors are reporting back the correct values. 

[jlr2267]

I'm no expert on wheel speed sensors, but I do know that the transfer case will not shift in to 4 low unless the wheel speed sensors are reporting back the correct values. 

I guess I’d better address the wheel sensor first, then go from there. This is getting more expensive the deeper I get. It’s what I get for buying these high mileage Chevy trucks I suppose.

[Supreme Pizza]

All depends. Some people spend $350,000 on a 1994 Suburban. Some people send $1,290 on a 2016 Suburban. Speed sensors at the dealer will cost thousands. Speed sensors on Amazon will cost pennies. 

[jlr2267]

To clarify, your "neutral" light for the transfer case has nothing to do with your transmission gear shifter selection. You have two neutral sections: transfer case and transmission. To select neutral on your transfer case, you need to hold down 2 transfer case shift buttons. For the transmission, you shift to N. 

Glad you clarified.

Interestingly, when I went through the procedure to put the T/C in neutral, and then back out of neutral, it went into 4L on its own. I drove it in 4L and so I know it works. Now, I just gotta figure out how to make it SHIFT into 4L like its supposed to with the button!

I sure miss my old manual shift.

[jlr2267]

Also checked the TC fluid and it is ATF. I thought GM trucks with Auto 4WD option were to get the blue AutoTrac II fluid..?

Will it do damage to leave the ATF? No plans to use “Auto”

[Supreme Pizza]

If your top transfer case control button round,  you need the AutoTrac II fluid. I would drain and refill it as soon as possible. Here is where I buy mine: 

 

 

https://www.amazon.com/ACDelco-10-4017-Auto-Trak-Transfer-Fluid/dp/B002H8U3KK/ref=sr_1_1_sspa?ie=UTF8&qid=1526138351&sr=8-1-spons&keywords=ACDelco+Auto-Trak+II+Transfer+Case+Fluid&psc=1

[jlr2267]

It’s the encoder motor. Just need to decide if 4L is worth spending the money. Everything else functions ok.

Thx for the help.