Transfer Case/ trans issue

[rockola1971]

You're welcome, man.

Let us know what t-case you have but your transmission limp mode itself is an entirely separate issue and by itself would not cause your lack of 4WD functionality (im assuming you're in neutral and stopped when trying to shift into 4WD). However shorts or other electrical problems upstream of your trans/tcase can be causing both the trans and tcase command/control problems you're having.

All that said, im not sure an incorrect tcase would even install in place of the correct NP246 (others can confirm or deny).

You can use most any Snap On scan tool, Autel as well as the more advanced OTC/SPX brand scanners to read chassis codes.

The Tcase in a 2003 LT would be a NP246E (E=enhanced). They made some improvements on the original NP246. The NP246/E does not require a stop or in neutral to go in or out of 4wd hi/2wd. Heck you can cruise down the highway at 70mph and put it in Auto4wd (which uses sensors to detect wheel slippage and engage the 4wd clutches) or you can go into 4wd Hi at 70mph. You of course couldnt do that with the old floorshift steel cased transfer cases (wouldnt do you any good since most you had to manually lock the hubs anyway). I own (2) 03 Tahoe LT's with the NP246E Tcase and they are stupid easy to troubleshoot and rebuild. It is very cost effective for a DIY project too. You are absolutely correct that the TCASE has nothing to do with the OP's Tranny problems. Tcase has its own control module and the tranny of course is controlled by the PCM.

I would check the wiring harness to tranny all the way back to the PCM for damage. Make sure harness wasnt spliced in by some dufus that got it all wrong. If that is all good then like you said it is time to drop the pan and inspect/test for damage/failure.

 

[NickTransmissions]

The Tcase in a 2003 LT would be a NP246E (E=enhanced). They made some improvements on the original NP246. The NP246/E does not require a stop or in neutral to go in or out of 4wd hi/2wd. Heck you can cruise down the highway at 70mph and put it in Auto4wd (which uses sensors to detect wheel slippage and engage the 4wd clutches) or you can go into 4wd Hi at 70mph. You of course couldnt do that with the old floorshift steel cased transfer cases (wouldnt do you any good since most you had to manually lock the hubs anyway). I own (2) 03 Tahoe LT's with the NP246E Tcase and they are stupid easy to troubleshoot and rebuild. It is very cost effective for a DIY project too. You are absolutely correct that the TCASE has nothing to do with the OP's Tranny problems. Tcase has its own control module and the tranny of course is controlled by the PCM.

I would check the wiring harness to tranny all the way back to the PCM for damage. Make sure harness wasnt spliced in by some dufus that got it all wrong. If that is all good then like you said it is time to drop the pan and inspect/test for damage/failure.

Interesting re the 246E. My 03 Tahoe Z71 has the 246 which when I shift into 4WD, I am in neutral, stopped. And agree, those TCs are very straight forward to service or rebuild.

 

[BowtieMafia66701]

I did just crawl underneath the ol tahoe and it is indeed a 246. But it dosent say e or anything on that just the 246 on the badge

 

[rockola1971]

Interesting re the 246E. My 03 Tahoe Z71 has the 246 which when I shift into 4WD, I am in neutral, stopped. And agree, those TCs are very straight forward to service or rebuild.

Do you have the auto 4 wd button at the top of your buttons?

 

[rockola1971]

I did just crawl underneath the ol tahoe and it is indeed a 246. But it dosent say e or anything on that just the 246 on the badge

None of them do. Its a 246e if its a 2003. Unless of course someone swapped in a standard 246. 1998-2002 were the standard NP246 used in GM K chassis.

 

[NickTransmissions]

Do you have the auto 4 wd button at the top of your buttons?

I do and all the buttons have little LED lights that illuminate based whichever range is selected (im always in 2HI). As far as I know, my transfer case is the original tcase that came with the vehicle when I bought it 10 years ago.

I replaced the tcase encorder motor assembly last year with a new AC Delco unit as the original failed (just swapping the sensor didnt work). Anyway, had to clear the chassis code for failed tcase motor then put the trans in neutral then shift the tcase into 2HI. Tcase was unresponsive until I placed the trans in neutral which is why I initially mentioned it.

Addl context in case anyone's wondering: I only do carry out/bench transmission builds; I dont ever see the vehicles they are installed back into. So not super versed on anything outside of the transmission beyond what I see/do on my own vehicles or those of family/friends.

 

[rockola1971]

I do and all the buttons have little LED lights that illuminate based whichever range is selected (im always in 2HI). As far as I know, my transfer case is the original tcase that came with the vehicle when I bought it 10 years ago.

I replaced the tcase encorder motor assembly last year with a new AC Delco unit as the original failed (just swapping the sensor didnt work). Anyway, had to clear the chassis code for failed tcase motor then put the trans in neutral then shift the tcase into 2HI. Tcase was unresponsive until I placed the trans in neutral which is why I initially mentioned it.

Addl context in case anyone's wondering: I only do carry out/bench transmission builds; I dont ever see the vehicles they are installed back into. So not super versed on anything outside of the transmission beyond what I see/do on my own vehicles or those of family/friends.

That neutral deal immediately happened after you changed out the encoder motor? If so then that is because it was lost and the Tcase computer didnt know what the encoder position was until you put it in neutral. Tomorrow go drive down a road at whatever speed and push the 4wd hi button and it will shift right into it. Completely normal operation.

 

[BowtieMafia66701]

So thought id post an update. I got out and starting looking at wires and checking fuses. Checked under the hood and everything was good. Then i checked the pcm and tcm fuse in the panel on the dash and well first off the fuse was too big it was a 15 amp and not a 10 and it was blown and had a random wire ran behind my cluster not hooked to anything which i assume it must of been ran to the radio or something. So basically changed that fuse to a good 10 amp fuse and now the ol girl runs great, shifts great and has plenty of power. So thanm you guya again for all the help and suggestions. Now i have the ease and worry of maybe needing major trans work done at rest. Cleared the codes and checked again and its not shooting anything and my engine light went off. So again a ton of thanks for the help guys.

 

[rockola1971]

I do and all the buttons have little LED lights that illuminate based whichever range is selected (im always in 2HI). As far as I know, my transfer case is the original tcase that came with the vehicle when I bought it 10 years ago.

I replaced the tcase encorder motor assembly last year with a new AC Delco unit as the original failed (just swapping the sensor didnt work). Anyway, had to clear the chassis code for failed tcase motor then put the trans in neutral then shift the tcase into 2HI. Tcase was unresponsive until I placed the trans in neutral which is why I initially mentioned it.

Addl context in case anyone's wondering: I only do carry out/bench transmission builds; I dont ever see the vehicles they are installed back into. So not super versed on anything outside of the transmission beyond what I see/do on my own vehicles or those of family/friends.

Your Tcase was bound up and couldnt physically move into another gear range because your tranny being in park would not allow the output shaft of the tranny to move any which of course is splined into the input of the Tcase. So the Tcase was all locked up and couldnt move internally enough for a postive shift.
These Tcases were engineered to be shifted on the fly except for of course 4L range. That keeps people from going xx MPH and then jamming it into 4L which of course sends the engine RPM's skyrocketing. I dont believe the low range has any kind of synchronization either.

 

[NickTransmissions]

Your Tcase was bound up and couldnt physically move into another gear range because your tranny being in park would not allow the output shaft of the tranny to move any which of course is splined into the input of the Tcase. So the Tcase was all locked up and couldnt move internally enough for a postive shift.
These Tcases were engineered to be shifted on the fly except for of course 4L range. That keeps people from going xx MPH and then jamming it into 4L which of course sends the engine RPM's skyrocketing. I dont believe the low range has any kind of synchronization either.

Yep, realized that part way through and shifted the trans into neutral. Then put all four wheels on stands so i could shift the tcase manually. I was then able to put the tcsse in neutral then install the encoder motor, clear the C codes, fire it up while in neutral and the select the tcase range (I run mine in 2H nearly 100% of the time) but it does shift into 4hi while moving as it should. Thanks, @rockola1971 .