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No 4LO

The wear issue can happen at ANY time. Theres been trucks lose transfer cases at 20K miles from it, then theres ones out there like my uncles who didn't wear through until 360K miles. It's all a crap shoot. And the steel plate should be installed as a preventative measure IMHO. I put one in mine FIRST thing after I got it home from the junkyard. Ended up I had an almost brand new one as it was built late 06 according to the date stamp on it, but came out of an 03 truck that had been in there yard since 07(I bought it in 09). Even with it being so new AND having GM's fix in it, the factory wear clip was almost worn through already.
 
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...

As far as I can tell there is no set time frame however a mechanic/fabricator I know believes it depends on how much the t-case is used. One done it will be good for the life of the t-case.

Since I had replaced mine after tow company towed and damaged the t-case I've not used GM's blue t-case fluid but AMSOIL full synthetic trans fluid after I learned it was OK to use from the manufacturer.
 
THEFERMANATOR said:
The wear issue can happen at ANY time. Theres been trucks lose transfer cases at 20K miles from it, then theres ones out there like my uncles who didn't wear through until 360K miles. It's all a crap shoot. And the steel plate should be installed as a preventative measure IMHO. I put one in mine FIRST thing after I got it home from the junkyard. Ended up I had an almost brand new one as it was built late 06 according to the date stamp on it, but came out of an 03 truck that had been in there yard since 07(I bought it in 09). Even with it being so new AND having GM's fix in it, the factory wear clip was almost worn through already.
Click to expand...

Who's the vendor for these plates? Does this ( maintenance) apply to my son's '94 as well as my electro shift '99. If it involves pulling the pump out, sound like I might as well replace the pump. Do you go with a new GM pump, or a reman?
 
Big T said:
Who's the vendor for these plates? Does this ( maintenance) apply to my son's '94 as well as my electro shift '99. If it involves pulling the pump out, sound like I might as well replace the pump. Do you go with a new GM pump, or a reman?
Click to expand...
Not the 94, only the ones with the 2 piece magnesium case. The NP241 does not have the problem. And theres no reason to replace the pump. I have yet to hear of one fail, even after being run dry they still work.

As to the fix, theres 2 options. I went with the plate because it was cheaper at the time. The other option is a new pump half that uses extra wide tangs to hold it in place so as to not cut into the soft magnesium. The price on them has come down from $225 to $80 for the pump half, sealer, and gasket.

http://www.ebay.com/itm/Transfer-Ca...36-246-261-263-261-XHD-BRNY4080-/121484954880
http://www.amazon.com/dp/B00F7SIG3S/?tag=jhuntlink-20
 
As an Amazon Associate we earn from qualifying purchases.
More confusion: one is simply a metal plate for $20, the other is a kit for $80. What's the difference?

So now I'm lost as to what goes out that costs me 4LO? Is it the transfer case module? Is that also referred to here as the encoder? Is it this transfer case pump motor? Or is it the Speed Sensor? I'm now completely lost.
 
FellowTraveler said:
Here's a link that will explain how the NP246 works:
http://www.chevyavalanchefanclub.com/cafcna/index.php?topic=41895.new
Click to expand...

Excellent link and article.

"When the ignition key is in the RUN position, the transfer case shift control module monitors the transfer case shift control switch to determine if the driver desires a new mode/range position. At a single press of the transfer case shift control switch, the lamp of the new desired position will begin flashing to inform the driver that the transfer case shift control module has received the request for a new mode/range position. The lamp will continue to flash until all shifting criteria has been met and the new mode/range position has been reached, or has been engaged. Once the new mode/range position is fully active, the switch indicator lamp for the new position will remain ON constantly."

Given my symptom of no 4LO and the switch indicator lamp flashing continuously, I'm concluding that the transfer case shift control module has received the request for a 4LO mode. The problem is that the shifting criteria have not been met and the mode/range positioin has not been engaged. This would suggest that it's a problem with Encoder Motor.

Am I interpreting this correctly?
 
You need to diagnose the issue, not throw parts at it. Buying parts can get REAL costly working on these systems. It could be the encoder motor not shifting to low, but this probem will normally exhibit the signs of the shift motor trying to shift. It's hard to tell if its trying as you cant really hear it trying over the sound of the 6.5L running. If it goes into other ranges but not 4 low, then it would stand a reason that it doesn't think all the criteria has been met for it to shift to 4 low. This could also be a bad TCCM not recognizing the conditions have been met.
 
THEFERMANATOR said:
You need to diagnose the issue, not throw parts at it. Buying parts can get REAL costly working on these systems. It could be the encoder motor not shifting to low, but this probem will normally exhibit the signs of the shift motor trying to shift. It's hard to tell if its trying as you cant really hear it trying over the sound of the 6.5L running. If it goes into other ranges but not 4 low, then it would stand a reason that it doesn't think all the criteria has been met for it to shift to 4 low. This could also be a bad TCCM not recognizing the conditions have been met.
Click to expand...

So would the dealer's Tech II be able to pull codes that tell me exactly what's wrong and what I need to replace?
 
It can tell you if theres codes, and then that will tell you which direction to go in. If you have any codes, then you can use the flow charts to go furthur.
 
Another consideration, in the owners manual vehicles equipped with AutoTrac should have the same tire pressure front/back this is required to give the controller more accurate data for smoother operation in auto mode.

I take it one step further by measuring distance from center of hub to tarmac (this gives you your loaded tire circumference) making front to back as close as I can get it.
 
Thanks but tire pressure is the same and everything works but 4LO. Bought the truck in 2010 and 4LO worked for like 2 years, then it went out and it has persisted as described. I will take it in to have codes read. Just not this weekend.
 
The speedo is run off the vssb and it receives its signal from the vss(sensor mounted in the rear of the t-case for 4x4's). The ecm modifies the speed input it receives from the vssb when in 4 low so it knowshow fast the trans output shaft is spinning so it shifts at the correct speeds in 4 low.
 
This is a good article on the Kelsey Hayes 310 that's in our trucks:

http://www.aa1car.com/library/abs_kelseyhayes.htm

It implies that you can pull codes Morse Code fashion by jumping across terminals:

KELSEY-HAYES 4WAL ANTILOCK BRAKE TROUBLE CODES
The 4WAL system provides manual flash codes, and can also be accessed with a scan tool. Here's the manual procedure.


1. Connect a jumper wire between pin "A" and pin "H" on the diagnostic connector under the instrument panel (or ground pin "H"), and turn the ignition on. This puts the system into the self-diagnostic mode.

2. Codes are displayed by flashes of the ABS warning light. Count the flashes to determine the code number. If the ABS warning light circuit is defective, the codes will be flashed out by the brake warning light.

The first series of flashes will represent the first digit of the fault code. The second series of short flashes that follow a brief pause represent the second digit of the code. A code 12, for example, would appear as a flash, pause, flash, flash.

One of the codes received will be a normal system code: code 12 with the brake not applied in the 2WD mode; code 13 with brake applied in 2WD mode; code 14 with brake not applied in 4WD mode; or code 15 with brake applied in 4WD mode. This normal code allows the brake and 4WD switches to be tested without having to use a scan tool.

Each code will repeat three times before the next code is displayed.

To erase stored fault codes, a scan tool or the following manual procedure can be used.

1. Turn the ignition switch on.

2. Connect a jumper wire or key between diagnostic connector terminals "H" and "A" (or ground "H") - and wait two seconds.

3. Remove the jumper wire for one second.

4. Repeat the grounding for two more seconds. The ABS warning light should go out if the codes have been successfully erased.

This procedure is necessary only on certain hard codes. Soft codes can be cleared by correcting the system problem and turning the ignition off for approximately five seconds.

KELSAY-HAYES 4WAL SCAN TOOL DIAGNOSIS
The Kelsey-Hayes 4WAL ABS system can also be diagnosed with a scan tool. However, a bi-directional scan tool with the appropriate software is necessary to read history codes and to perform various tests. These include:


  • Check voltages at the diagnostic connector terminal "H."
  • Wheel speed sensor output (in miles-per-hour) from each sensor.
  • Reset switch status (right front, left front and rear).
  • Function tests of the hydraulic modulator.
  • Capture "snapshot" data during a test drive for later analysis.
History codes in the 4WAL system reveal the number of ignition drive cycles since a fault occurred. A drive cycle is defined as the vehicle being started and driven above a specified speed, usually about eight mph with the 4WAL system.

Attached are additional diagnostic tests for the Kelsey Hayes 310.
 

Attachments

  • Kelsey_Hayes_310_Ground_Connection_Diagnostics.pdf
    43.7 KB · Views: 4
  • Kelsey_Hayes_310_Wheel_Speed_Sensor_Diagnostics.pdf
    293.2 KB · Views: 2
More in-depth info for the 246 AUTOTRAC
 

Attachments

  • nv 246 CAN'T FIX IT 2004_12.pdf
    423.4 KB · Views: 5
  • NV 246 TRICKS 2005_09.pdf
    609.2 KB · Views: 6
THEFERMANATOR said:
Not the 94, only the ones with the 2 piece magnesium case. The NP241 does not have the problem. And theres no reason to replace the pump. I have yet to hear of one fail, even after being run dry they still work.

As to the fix, theres 2 options. I went with the plate because it was cheaper at the time. The other option is a new pump half that uses extra wide tangs to hold it in place so as to not cut into the soft magnesium. The price on them has come down from $225 to $80 for the pump half, sealer, and gasket.

http://www.ebay.com/itm/Transfer-Ca...36-246-261-263-261-XHD-BRNY4080-/121484954880
http://www.amazon.com/NP261HD-NP261XHD-NP263XHD-TRANSFER-ALUMINUM/dp/B00F7SIG3S/ref=pd_sbs_263_2?ie=UTF8&dpID=41DP-c4K5lL&dpSrc=sims&preST=_AC_UL160_SR160,160_&refRID=1N7TVMBHJ03KAX2ZYHMB
Click to expand...

There aluminum case halves for the t-cases prone to pump rub through that eliminate the pump rub through problem.
http://www.transfercases.com/replacement.case.shell.htm
 
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