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No 4LO

Big T

Big T

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My 1999 with push buttons for transfer case will not shift in to 4LO. Tried in Neutral, Drive, etc. Light never comes on. Everything else works: 2HI, AWD, 4HI. What should I look for?
 
Have you made sure you met all the requirments for it to shift? Rolling at 2-5 MPH, trans in nuetral, then push the 4 low button? If so you may have a speed sensor issue in the t-case, bad switch, or an encoder motor problem.
 
Have you made sure you met all the requirments for it to shift? Rolling at 2-5 MPH, trans in nuetral, then push the 4 low button? If so you may have a speed sensor issue in the t-case, bad switch, or an encoder motor problem.
 
THEFERMANATOR said:
Have you made sure you met all the requirments for it to shift? Rolling at 2-5 MPH, trans in nuetral, then push the 4 low button? If so you may have a speed sensor issue in the t-case, bad switch, or an encoder motor problem.
Click to expand...

Went out to test again. Got it rolling in neutral 2 mph. Press 4LO and the light flashes rapidly and stays that way.

Switch at the dash is new. So that leaves speed sensor in the t-case or encoder motor problem. Where are these and how do I address and in which order?
 
The encoder motor is the large black plastic shift motor on the side of the t-case. Sometimes portions of the sensor portion in it go bad, and it wont shift past the bad spot. Some have said they need to be still for theres to shift to 4 low. The speed sensor that gives trouble is the one on top of the t_case above the driveshaft going to the front diff.
 
Are there tests to determine if there is a problem with the speed sensor or the encoder? Or do you simply buy parts and replace to see if that fixes the problem?
 
Get a scanner on it and see what teh TCCM is seeing. It can force it to go through it's range and see if the encoder works or not. Let me look, but there used to be some people out there who had pulled there encoders apart and repaired the contact problems. Nprmally the speed sensor problem will also cause issues wit hthe auto 4WD. It uses that sensor to tell it front driveshaft speed VS rear shaft speed so it knows when to engage the clutch pack for 4X4 when in auto.
 
Check the fluid level in it first. It appears as though the NP246 also sufferred from the infamous pump rub problem due to the magnesium case. Most all problems point to the encoder motor on that case, but it's PRICEY $$$.
 
Also I read if theres a problem with a speed sensor input from the ABS or an ABS problem, it can disable 4 low. The T-case control module uses input from the ABS and the front shaft speed sensor for controlling the 4 wheel drive and shifting.
 
Is this the Encoder or Control module you speak of:

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$243.79 $25.00 $268.79

ACDELCO 15025394 GM Original Equipment; Reman Info
ELEK SHFT transfer CASE(NP1)
 
THEFERMANATOR said:
Thats the TCCM, transfer case control module. Heres an encoder motor. Don't go throwing parts at it. You will be cheaper to find somebody with a scanner to check it and find the problem than to throw parts at it.
http://www.fullsizechevy.com/forum/...-encoder-motor-sensor-replacement-w-pics.html
Click to expand...

So I need to take it in to the dealer to have these codes pulled on a Tech II?

I am not getting the Service 4wd light and never have. 2Hi, AWD, 4Hi have always worked, every time. I just lost 4Lo sometime after I purchased the vehicle in 2010. The poster in the thread was complaining of intermittent light and function.

I did order a RF speed sensor for the ABS to play with that before giving up and taking it in.
 
Not neccesarily the dealer, but you need a higher end scanner that can access the tccm to see what it is seeing.
 
THEFERMANATOR said:
Check the fluid level in it first. It appears as though the NP246 also sufferred from the infamous pump rub problem due to the magnesium case. Most all problems point to the encoder motor on that case, but it's PRICEY $$$.
Click to expand...
They do suffer pump rub through and towing a NP246 w/o putting it into neutral will destroy it too been there done that....
 
FellowTraveler said:
They do suffer pump rub through and towing a NP246 w/o putting it into neutral will destroy it too been there done that....
Click to expand...

Can someone explain the "pump rub" thing in a simple and concise manner? I read all the pump rub threads here last night and they all refer to the pump rub, but never really describe what it is and the symptoms. It took me several threads to figure out this was on the transfer case. The sticky on this page just left me scratching my head.
 
They used a magnesium case housing and an aluminum pump housing. The pump inside the transfer case has 4 tangs about an 1/8" thick and about an inch wide to keep the pump locked to the case so it doesnt spin in the housing. Aluminum is harder than magnesium, and over time those thin pump tangs will wear through the magnesium housing creating a leak letting the fluid come out. Then your transfer case runs out of oil, and burns up.

They make a coated steel wear plate to sit in between the transfer case housing and pump to prevent this from happening.
 
How do you ID which ones need the correction, and is there a mileage to say you NEED to tear apart and fix?

Obviously sooner better than later, but if you buy a truck with say150,000 on it- do you tear it apart before you start driving it, knowing your close to the edge?
 
Will L. said:
How do you ID which ones need the correction, and is there a mileage to say you NEED to tear apart and fix?

Obviously sooner better than later, but if you buy a truck with say150,000 on it- do you tear it apart before you start driving it, knowing your close to the edge?
Click to expand...

I'm with Will L. on this question. Is this steel wear plate something I need to get and install for preventative maintenance?

Sorry about this flurry of questions regarding brake mods, ABS and this Transfer case issue, but these are items that have been deferred while I was remodeling the second home. The ABS and 4Lo weren't mission critical, so I just deferred on them until now. Seems like I got a window to address things on our vehicles, so that's what I'm up to.

My real issue of the moment is my wife's damn SLK 280 which I posted on in the Other Gas Engines Forum. Hate that thing. The same issue of misfiring on cylinders 1-4 occurred when I repaired the old manifold and reinstalled it, then when I installed a new manifold. I only touched a few things during the work and I've gone through them all. I may try one more effort with new gaskets as they're prone to moving around during the install. If that doesn't work, I need to take it in and with Mercedes, they bend you over. I'm not comfortable with that.
 
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