Transfer Case/ trans issue

[BowtieMafia66701]

Hey guys,

I just got a 2003 tahoe LT 4x4. I have a few questions i am trying to figure out. When i got it the guy said he put a used transmission in and he wasnt sure if it has the right transfer case or not. So i am curious how i can find out what transfer case goes in it i want to make sure its the right one because i know its gonna need some trans work i am assuming.


Secondly, i need some advice hooked up my code reader because when i am driving it dosent seem right. It runs well but i am not seeing or feeling any shifting. I think its in 3rd or 4th gear. But i got a few codes which tells me its gonna need work. Ive attached most of the codes i got. I am wondering if its worth it to replace the parts its saying is wrong or go ahead with a rebuild or take it to a shop and have the whole thing replaced. Which is why i am trying to find out what transfer case is supposed to go on it. Any help or advice would be greatly appreciated.

 

[Fless]

Do you have the 2-speed switch on the dash? It would have AUTO, 2HI, 4HI, and 4LO buttons. If so, that's the NP246 case. You can also crawl under and look for the tag on the case:

If your dash switch is different, post up a pic of it, or of your full RPO code sticker that's inside the glovebox lid.

 

[BowtieMafia66701]

This is my switch. Only why i am asking is he said he put another transfer case on it but he wasnt sure it was the right one and there was a few different ones.

 

[Fless]

See if there is a tag on the transfer case; also look at your RPO codes and look for an NP8 code. If it's not there, post up the other "Nxx" codes and we can tell you what it came with originally.

Do you know if that dash switch was changed? The earlier models had the gray buttons (yours looks gray to me), but the 2003-2006 models had black buttons, and they're different switches based on part numbers. But I'm not sure how they're functionally different.

 

[BowtieMafia66701]

It does have the np8 code. The dash i am sure has been out thats another issue i have to fix is they put a escalade cluster in and nothing works on it. So i know the dash has been apart but i dont know if they changed the buttons or not. I am gonna assume they did.

 

[NickTransmissions]

Hey guys,

I just got a 2003 tahoe LT 4x4. I have a few questions i am trying to figure out. When i got it the guy said he put a used transmission in and he wasnt sure if it has the right transfer case or not. So i am curious how i can find out what transfer case goes in it i want to make sure its the right one because i know its gonna need some trans work i am assuming.


Secondly, i need some advice hooked up my code reader because when i am driving it dosent seem right. It runs well but i am not seeing or feeling any shifting. I think its in 3rd or 4th gear. But i got a few codes which tells me its gonna need work. Ive attached most of the codes i got. I am wondering if its worth it to replace the parts its saying is wrong or go ahead with a rebuild or take it to a shop and have the whole thing replaced. Which is why i am trying to find out what transfer case is supposed to go on it. Any help or advice would be greatly appreciated.

You're trans is in limp mode (has nothing to do w/the Tcase which if you have the np246 installed (RPO code = NP8) is correct for your vehicle. If you had an issue with the tcase (electrical, anyway), you'd throw a chassis/tcase code and that's usually encoder motor sensor or the motor itself is bad.

When I see that many codes on one vehicle for the transmission, my first suspection is an electrical short to ground somewhere, either internally inside the trans (perhaps bad harness) or externally.

Check external grounds then make sure you're at least getting 12v to the trans. If everything looks/checks good on the outside, drop the pan and start ohm'ing out all your solenoids. The two shift solenoids (A & B) + the 3-2 solenoid should all read between 20-22 ohms; the PWM solenoid should read 9-11 ohms and the electronic pressure control solenoid should read 4.5-6 ohms. If they all check ok, id replace the harness and pressure switch manifold assembly and see if that fixes the problem.

 

[BowtieMafia66701]

You're trans is in limp mode (has nothing to do w/the Tcase which if you have the np246 installed (RPO code = NP8) is correct for your vehicle. If you had an issue with the tcase (electrical, anyway), you'd throw a chassis/tcase code and that's usually encoder motor sensor or the motor itself is bad.

When I see that many codes on one vehicle for the transmission, my first suspection is an electrical short to ground somewhere, either internally inside the trans (perhaps bad harness) or externally.

Check external grounds then make sure you're at least getting 12v to the trans. If everything looks/checks good on the outside, drop the pan and start ohm'ing out all your solenoids. The two shift solenoids (A & B) + the 3-2 solenoid should all read between 20-22 ohms; the PWM solenoid should read 9-11 ohms and the electronic pressure control solenoid should read 4.5-6 ohms. If they all check ok, id replace the harness and pressure switch manifold assembly and see if that fixes the problem.

Thank you very much for the information. Greatly appreciated. Only reason i asked about the tcase is the guy who i got it from didnt know if it was the right one. So i am gonna slide underneath and check it out on my day off. I tried engaging 4 wheel drive but it did nothing. So i wonder if the limp mode could cause this or it is the wrong transfer case. Just wanting to make sure everything is right before i start getting it all fixed. But again thank you again for the info

 

[Fless]

You will need a more advanced scanner to be able to read the 4x4 codes, if there are any. If you have a DIC (Driver Information Center) are there any messages on it? Maybe not with that cluster being dead.

 

[NickTransmissions]

Thank you very much for the information. Greatly appreciated. Only reason i asked about the tcase is the guy who i got it from didnt know if it was the right one. So i am gonna slide underneath and check it out on my day off. I tried engaging 4 wheel drive but it did nothing. So i wonder if the limp mode could cause this or it is the wrong transfer case. Just wanting to make sure everything is right before i start getting it all fixed. But again thank you again for the info

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.

 

[Fless]

If it's the NP246 t-case (almost guaranteed) you can switch between AUTO, 2HI, and 4HI modes on the fly. For going in and out of 4LO you need to be in neutral, at a standstill or rolling slow, less than 3mph. Download a copy of your owner's manual from GM's website for the skinny.

 

[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 .