3.42 to .373

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
Hey everybody, i got an 03 TB EXT 4.2 I6 and somebody before me swapped the engine. When i got it the 4x4 didn't work (still doesn't) i found out that my front and rear differentials were different. My stock gears were 3.42 and the front end was swapped to a 3.73, so, naturally i swapped the rear to match because forget doing the front. Now, i have a few questions.
1. How would i go about fixing the speedo problem? (reads higher than my actual speed)

2. How do i reset the 4x4 system? My selector lights aren't lighting and rear dif doesn't engage.

3.what th F$@! Do they mean by differential core?
 

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
Say what? Is the transfer case in neutral then and the vehicle does not move under it's own power at all?
She moves when the switch is in 4HI under its own power, i just don't hear the tranfer case engage and the lights on the selector don't light up. Figure i need to reset the 4x4 system, bit I'm not 100% sure on how to do that.
 
Last edited:

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
There should be 2 sounds when switching from or to 2Hi. One comes from the front axle disconnect and a shorter sound from the transfer case shift motor.

Front axle disconnect....


Transfer case shift motor, commonly called an encoder motor. Mine struggles a bit.....



The lights are powered by the BCM under the rear seat and the TCCM supplies the ground as needed. It's done this way so the BCM can dim the indicator lights.
 
Last edited:

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
For the indicator lights... See if the headlamps ON and front foglamps ON indicator lights work. They share the power from the BCM that lights the 4WD indicator lights. If these lights work but the 4wd lights don't it could be wiring at the switch or the tccm.
 

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
There should be 2 sounds when switching from or to 2Hi. One comes from the front axle disconnect and a shorter sound from the transfer case shift motor.

Front axle disconnect....


Transfer case shift motor, commonly called an encoder motor. Mine struggles a bit.....



The lights are powered by the BCM under the rear seat and the TCCM supplies the ground as needed. It's done this way so the BCM can dim the indicator lights.
I get the front disconnect sound but not the encoder motor. If its just the selector lights (they worked before the swap) and the encoder motor would that mean my tccm is bad?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
If it moves with the switch in 4Hi but not otherwise then I would think the encoder motor must be moving at least some. The recorded sounds are louder because the phone was under the truck and it's possible your encoder is quieter than my old original? You might not hear it?? If it were not moving at all I would think there wouldn't be a difference whether in 4Hi or anywhere else.

The lights not working is a strange thing if they worked before but not now. Be certain the dimmer isn't turned down? How about those headlamp and foglamp indicators? Do those work and dim correctly?

I try not to jump to conclusions about modules like the TCCM being "bad". I prefer to troubleshoot and prove something is bad before randomly tossing parts at an issue. Could be loose wiring.
 

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
If it moves with the switch in 4Hi but not otherwise then I would think the encoder motor must be moving at least some. The recorded sounds are louder because the phone was under the truck and it's possible your encoder is quieter than my old original? You might not hear it?? If it were not moving at all I would think there wouldn't be a difference whether in 4Hi or anywhere else.

The lights not working is a strange thing if they worked before but not now. Be certain the dimmer isn't turned down? How about those headlamp and foglamp indicators? Do those work and dim correctly?

I try not to jump to conclusions about modules like the TCCM being "bad". I prefer to troubleshoot and prove something is bad before randomly tossing parts at an issue. Could be loose wiring.
I dont think mine is much quieter than yours was. I could hear it before, better than i could hear the front disconnect. The lights all dim like they're supposed to, its just the selector switch not lighting up anymore. Isnt there a way to reset the 4x4 system? If so, should i try that?
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
I imagine the lights might be due to an error in the system. The TCCM will disable the system under some error conditions I think. Disconnecting power to the TCCM for a few minutes will reset it believe. Pull out the 25 amp ATC fuse in the underhood fuseblock.
 
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GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
I imagine the lights might be due to an error in the system. The TCCM will disable the system under some error conditions I think. Disconnecting power to the TCCM for a few minutes will reset it believe. Pull out the 25 amp ATC fuse in the underhood fuseblock.
Thanks, I'll have to wait until tomorrow to try it.
 
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Mektek

Member
May 2, 2017
656
FL
If the lights on the selector are not lit, then the tccm has shut down. You should also have a service 4wd light. With the mismatched differentials the tccm sensed a speed difference between the front and rear driveshaft and that could be enough to shut it down.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
The rear diff should always be connected to the transfer case except when in it's in neutral (selector turned and held beyond 4lo with a red N lit). Check to see if it's in neutral. Maybe the encoder motor isn't working properly or the transfer case is stuck in between 4x4 and neutral and when the front disconnect engages, it engages the front wheels only. Take the encoder motor off the transfer case and see if it moves when you change modes on the selector. If it does, your transfer case is possibly stuck but the TCCM should have thrown a service 4x4 light.

The TCCM sounds like it's still alive. If the lights on the selector aren't coming on at all, you should be getting a service 4x4 light on. If not, something may be going on with the wiring at the switch, TCCM or BCM. You can access the TCCM through the access panel in the upper left side of the dash and from under the dash. Download the manuals in my signature for the schematics to check for power and continuity.

For the speedo, you have two choices. Either find a PCM from a same year and engine truck that had the same gears or have your PCM reflashed with with a VIN of a truck with those gears.
 
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GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
If the lights on the selector are not lit, then the tccm has shut down. You should also have a service 4wd light. With the mismatched differentials the tccm sensed a speed difference between the front and rear driveshaft and that could be enough to shut it down.
So a reset should do the trick? I do have a spare tccm as well.
 

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
The rear diff should always be connected to the transfer case except when in it's in neutral (selector turned and held beyond 4lo with a red N lit). Check to see if it's in neutral. Maybe the encoder motor isn't working properly or the transfer case is stuck in between 4x4 and neutral and when the front disconnect engages, it engages the front wheels only. Take the encoder motor off the transfer case and see if it moves when you change modes on the selector. If it does, your transfer case is possibly stuck but the TCCM should have thrown a service 4x4 light.

The TCCM sounds like it's still alive. If the lights on the selector aren't coming on at all, you should be getting a service 4x4 light on. If not, something may be going on with the wiring at the switch, TCCM or BCM. You can access the TCCM through the access panel in the upper left side of the dash and from under the dash. Download the manuals in my signature for the schematics to check for power and continuity.

For the speedo, you have two choices. Either find a PCM from a same year and engine truck that had the same gears or have your PCM reflashed with with a VIN of a truck with those gears.
Yes, i have a service 4x4 light, sorry, i should've included that to the OP. Thanks for the info, im going to download them now.
 

GreenMachineTB

Original poster
Member
Aug 13, 2020
20
Washington
Hey everybody, i got an 03 TB EXT 4.2 I6 and somebody before me swapped the engine. When i got it the 4x4 didn't work (still doesn't) i found out that my front and rear differentials were different. My stock gears were 3.42 and the front end was swapped to a 3.73, so, naturally i swapped the rear to match because forget doing the front. Now, i have a few questions.
1. How would i go about fixing the speedo problem? (reads higher than my actual speed)

2. How do i reset the 4x4 system? My selector lights aren't lighting and rear dif doesn't engage.

3.what th F$@! Do they mean by differential core?
UPDATE: disconnected the battery and pulled the 4x4 fuse for 30 minutes plugged it all back in and se was good to go. Selector lit up, switched it to 4HI and everything engaged. THANK YOU EVERYBODY!! Now i just need to get the speedo part squared away and she'll be good to go.
 

TJBaker57

Member
Aug 16, 2015
2,897
Colorado
UPDATE: disconnected the battery and pulled the 4x4 fuse for 30 minutes plugged it all back in and se was good to go. Selector lit up, switched it to 4HI and everything engaged. THANK YOU EVERYBODY!! Now i just need to get the speedo part squared away and she'll be good to go.

Glad it worked out!

So for future reference the 4WD fuse under the rear seat powers the front axle disconnect but not the TCCM. The ATC (Automatic Transfer Case) fuse under the hood powers the TCCM but not the front axle disconnect.
 
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