NP 246 4 Lo not working

[Big T]

This is an old problem on the NP 246 transfer case in my 1999 K2500 Suburban: 4Lo does not work. Light on button just flashes. 2Hi, 4Hi and AWD all work.

I recently replaced both 4L80e transmission and the NP 246 transfer case. Also bought a new AC Delco encoder motor which did not work per my mechanic:

"Transfer case would not shift after replacement. Test power and grounds to motor = ok. Replacement shift motor is not moving. Installed original transfer case motor and test - 4wd now functions properly."

He missed the part about 4Lo not working, which is why I bought the new encoder motor. 4Lo still does not work. Light on dash button just flashes endlessly. Everything else works. New reman transfer case came with HD aluminum case half that addresses the pump rub issue.

Given that the AC Delco encoder motor did not work, I am sending that back as it was purchased on Amazon.

I still face the issue of no 4Lo. I have a CKO GM Tech 2 Scanner. I plugged in the scanner and got these screen captures:



Not sure I am using the Tech 2 properly. I tried to find how to run test for TCCM specific codes, but could not figure that out. Is this point to the Transfer Case Control Module (TCCM)?

 

[MrMarty51]

I wonder it the 4WD LOW Disabled function is something turned off within the Power Train Control Module ?
Disabled to Me would seem that it would need to be enabled as that is not a trouble code, at least thats the way it seems in My mind.

 

[THEFERMANATOR]

Does your gear display show N when you're trying to shift into 4 low? The most common problem I see is bad nsbu switches not displaying they are in neutral. If the tccm does not see neutral, it will do as you describe.

 

[THEFERMANATOR]

I wonder it the 4WD LOW Disabled function is something turned off within the Power Train Control Module ?
Disabled to Me would seem that it would need to be enabled as that is not a trouble code, at least thats the way it seems in My mind.

The tech 2 only shows disabled(off) or enabled(on).

 

[Big T]

Does your gear display show N when you're trying to shift into 4 low? The most common problem I see is bad nsbu switches not displaying they are in neutral. If the tccm does not see neutral, it will do as you describe.

If you are referring to the gear position indicator on the dash, then yes when I have it at N, 4Lo simply flashes:

March 25, 2022

youtube.com

nsbu = ?

 

[btfarm]

N eutral S afety B ack U p switch.

 

[Big T]

N eutral S afety B ack U p switch.

The NBSU was $39 so I ordered one.

 

[RI Chevy Silveradoman]

Could be bad ground or a bad switch. At least for the 2006 NP263XD Duramax transfer cases. Mine is doing the same exact thing. I started with the ground. It was fine, but I ran a wire as a backup to a good source up front. I don't have a means of testing, so I replaced front actuator in front axle, I went to replace encoder motor but was sent the wrong one so I'm still waiting to see if that fixes my issue. Lastly I'll replace the switch.
If that don't work, I'll have me a 2wd 2500HD. Lol

 

[Big T]

Found this article, though not sure if it is completely helpful:

A Guide to the NV 246 Transfer Case (transmissiondigest.com)

I got the AC Delco Encoder Motor returned and received full credit.

I canceled the transmission and transfer case order with Transmission Exchange Company in early February. They called me in the Middle of March to let me know that my transmission and transfer case were ready. Apparently, the belligerent employee I spoke with did not inform his boss/owner that I canceled the order. The boss/owner never called me. My credit card records showed them billing me $4,275 on 2/14. A call to Chase indicated they reversed $3,820 on 3/18 for a difference of $455. I called and left a message with Transmission Exchange Company and they called me back. The difference was due to the encoder motor they ordered and could not return, plus credit card fees. I simply told them to ship the encoder motor to me in Montana. I'll eat the credit card fees. So were done and I may have a use for the encoder motor.

So my replacement transmission was free, as it was sitting behind my garage. The reman transfer case cost me $1,100 with shipping. The install cost me $1,532, but that also included installation of power steering lines and engine + transmission mounts. Overall, not too bad and the truck runs great. Just need to figure out this non-working 4 low issue, which has been going on for years.

 

[RI Chevy Silveradoman]

Have you checked the switch yet?

 

[Big T]

Have you checked the switch yet?

I don't know how to check it. Waiting for the replacement to arrive.

 

[RI Chevy Silveradoman]

I'm not sure how to check it either.

 

[MrMarty51]

Me too dont know how to check it.
I would think that different positions should turn on or off different grounds but whose to say.
What say You @THEFERMANATOR

 

[Big T]

Well I've narrowed it down to one of 3 things: 1) Encoder Motor (new one on its way), 2) NBSS (new one on its way), and 3) Transfer Case Control Module (TCCM). The TCCM is a pricey ranging up to $340 depending on who is making it. Wish there was a definitive test I could run on the TCCM.

 

[Big T]

Some pics of the old transmission from the ‘99 Suburban….

 

[THEFERMANATOR]

Some pics of the old transmission from the ‘99 Suburban….
View attachment 73478View attachment 73479View attachment 73480View attachment 73481View attachment 73482

That is a late 99 build 4l80e, you can tell by it having the mounting tab at the 12 o clock position. Never seen a 6.5l with the top mounting tab before.

 

[BIGR]

That is a late 99 build 4l80e, you can tell by it having the mounting tab at the 12 o clock position. Never seen a 6.5l with the top mounting tab before.

Eagle Eye, THEFERMANATOR sure can spot that stuff, as we all knew, DANG he is good.

 

[Big T]

That is a late 99 build 4l80e, you can tell by it having the mounting tab at the 12 o clock position. Never seen a 6.5l with the top mounting tab before.

And yet I think the truck was a March '99 build, so it did not get the Optimizer 6.5 with block casted by International Harvester.

Q: What is the thread size for that front boss for the transmission line? I need to plug it with a bolt because it keeps burping ATF.

 

[THEFERMANATOR]

Which boss are you talking about that needs plugged?

I had my tech2 out earlier, to get into the autotrac tcase, select your vehicle, go under diagnostics, powertrain, and there will be 3 options, engine, trans, or atc, select atc as that is the transfer case.

 

[Big T]

Which boss are you talking about that needs plugged?

I had my tech2 out earlier, to get into the autotrac tcase, select your vehicle, go under diagnostics, powertrain, and there will be 3 options, engine, trans, or atc, select atc as that is the transfer case.

I was able to get one of those soft plastic cup plugs screwed into the front boss to stop the leak. We then move the trans to an equipment area of the basement, far, far away. I’ll deal with rebuilding it later.

I will play with the Tech 2 again.