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Discussion Starter #1
So I have managed to add a switch that basically tricks the transfer case computer into locking the transfer case in both 4Hi and 4Lo in any gear not just 1st gear 4Lo as the 01-02 models are wired. If you chose to follow these instructions you are taking the same risks I did and I assume no responsibilty for the results of your actions, only do this if you are confident in the job you are performing. I would like to thank new member motileracing for all his help, I tracked him down through Total Chaos Fab sometime ago when I found a pic of his white seq on this forum that had "transfer case mod" in his picture description. He modded his to lock in 4lo only in a slightly different a more precautionary way. Some of his steps now we know were overkill and I have not shown the full way he did his mod.

Basically there are two wires that recieve signals into the "4WD Control" module as it is labeled. The module is behind the dash between the stereo and glove box.

1st wire: The Blue-Red wire receives a ground signal to tell the module that the transfer case lever is in low range. The module must receive this signal in order to lock the transfer case when it is is signalled on the green wire. If you don't touch this wire the case will only lock in low range when you mod the green wire. Modding the Blue-Red means you tell the module it is in low range even though it may* be in high range.

2nd wire: The light Green wire receives a 12VDC signal to tell the module the transmission is in 1st gear. Sending 12VDC on this wire locks the transfer case immediately if the transfer case shift lever is in 4Lo or if the 4WD module thinks it is in low range by the ground signal it receives on the Blue-Red wire.

If you read this thread before you may have read that I was setting off the CEL but I have corrected this by adding a diode on the Red-Blue wire between the Engine ECU / L4 Shifter and the 4WD Module / new switch point. Note that I also found you can simply cut the Blue-Red wire and use no diode, this will make the truck have 2WD Low range, I didn't test this much other than a drive around the block in lo range, it didn't seem to cause any problems. Here is the wiring diagram with the 2 diodes, this is exactly how my truck is wired:



You can do this mod 2 ways, if you chose to only mod it so that the transfer case locks in 4Lo you will only mod the Green wire. If you mod the Red-Blue wire with an incorrectly placed diode or without one you will set off code P1782 "trensfer L4 SW Circuit Malfunction" as it called in my scan tool.



In any case throwing the switch in any gear at any speed Hi or Low range puts the truck into 4WD and locks the transfer case. Setting the switch off unlocks the case but leaves the truck in AWD. Press the normal 4WD button and the the truck goes back to two wheel drive. The orange and green lights on the truck all act normal and tell you what is going on, that is why I used an unlighted switch.

You will need:
1 single pole double throw switch, I used a cole hearse switch that fits the dash nicely
2 diode good for 1A or more (I used 6A diodes)
1 1A fuse
wire 16awg should be good, I used 14 which was obviously overkill but I had it already

Switch directly left of the steering column:



"Cole Hersee 58027-06" DPST switch (Double Pole Single Throw):



Steps
1. Disconect the negative terminal of the battery

2. Remove the glovebox, stereo, kick panel under the steering column
-Glovebox has two screws at base, plastic panel behind has 3 screws
-Stereo/HVAC surround has two screws inside top vents then pull unit off
-Kick panel has 10mm bolts in obvious spots





3. 4WD Control module has 10mm bolt holding it it place. Disconnect it for ease of access. Connect switch so you send ground to the Blue-Red wire and 12VDC to the green wire. Connect a diode in line on the Red-Blue wire towards the engine ecu / L4 shifter of the connection point. I pulled ground and ACC 12VDC off the back of the cig lighter. on the 12VDC I connected a diode so that if my accessory fuse blew, devices connected to my cigarette lighter would not pull current back through the controller. I also added a 1A fuse. I cut the green wire coming from the shifter column so I would not send 12VDC back that way in case that could harm something else, you could add a diode here as well, motileracing did this along with other things and his has been working for years without issue. This makes it so that in 4Lo 1st gear the transfer case does not lock, no big deal use the NEW SWITCH :D.









Everyone should know I will edit this post as things progress but at this point I believe I am done! The testing over the last few days has done well, I have driven the truck as fast as 100kmph in 4Hi all locked and it worked well. I occasionally have had the skid control come on a little over-actively but I am quite sure this is related to the steering rack bushings and brakes just getting done, I'm going for an alignment and zero point calibration on Apr 16 and that should correct this.
 

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Subscribed and gave you rep
 

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Discussion Starter #3
Thanks, I've taken it out wheeling a couple times and all seems good, I've used the new switch many times in 4Hi and 4Lo and had no issues. The dash indicators always tell when it's locked and all is good. Thanks for the rep!

Here's some pics from wheeling, I can tell when on three wheels the traction control works much less harder when the case is locked, smoother uphills too on off camber situations - just better overall! :D





 

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Discussion Starter #8
Nem, Do you have the part # for the switch?
Greg
It is a "Cole Hersee 58027-06" DPST switch. (double pole single throw - updated above too)


http://www.colehersee.com/pdf/A-Rockers.pdf

I bought it at Southern Interior Truck Electric in Penticton BC 250-492-0314

I included the link above as there is also other lighted switches that fit in that spot but interestingly I didn't notice until now that is the only DPST switch available in that 580XX-0X series of switches. I don't know how many people on the forum know about this series of Cole Hersee switches fit in almost all years of Toyota trucks back to about 1984. I think the 58027-17 fog light switch would look good there (if you want a fog light switch in that spot) and I am wondering if the M-58031 20A waterproof series would fit there, then it'll look like an ARB switch.
 

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I don't want to sound like a complete idiot but what is the advantage of this mod
does it do anything special like lock up the front and rear diffs
why not just use the exsisting 4 wheel button
 

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I don't want to sound like a complete idiot but what is the advantage of this mod
does it do anything special like lock up the front and rear diffs
why not just use the exsisting 4 wheel button
01-02 Transfer Case only locks up in 4L, transmission L. Locking up the transfer case changes it from full time 4WD to part time 4WD which changes the power distribution to a constant 50% front, 50% back. The mod Nem developed :tu: enables locking the transfer case regards of the transmission gear selection and also enables locking in 4H, like the 03+ sequoias. With this mod the 01-02 will lock similar to the 03+ in addition 01-02 have VSC off. I think the difference is the 03+ does a 40/60 distribution when locked.

Advantage of locking the Tranfer Case like the 03+ is higher speed off roading. I think it would be great in soft sand.

The mod does not affect the front or rear diff. The front and rear are typically open, although some may have an LSD in the rear. Traction control modifications (such as ARB air locker, Detroit, ... ) need to be installed if want to lock the front/rear.
 

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Even though VSC is off when center diff is locked a-trac still functions, therefore you still have "LSD" on both axles without the loss of traction if one wheel is in the air. Just remember not to lock up on high traction surfaces.
 

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Discussion Starter #13
That's a big stretch calling A-trac an "LSD".
Ya I wouldn't call it that either but having A-Trac working with the mod helps traction for sure, way easier to drive on 3 wheels now! It basically makes the A-Trac work much less harder, allowing it to work better.

Just an update too, it is still working great in my rig, no issues. I'd love to hear if anyone else has completed the mod, I only know of one member working on it :tu:
 

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Howdy Nem! I installed this mod along with a rear ARB locker in 2003 on my 2001 limited. I use the mod mainly in deep snow (but a variety of soft and hard surfaces as needed) and it works great. It has worked flawlessly for 7 years and I put on a minimum of 1,000 off road miles per year. The truck has never let me down and amazes freinds and bystanders. No issues!

I highly recommend this mod if you are going to "off-road" the truck. The stock AWD system is just not enough... even with the ability to lock the center dif in low range and low gear. The biggest issue is the fact that you need to drive the truck 10-15 feet forward to lock the diff, but this is not always an option especially if you are already stuck. And in difficult terrains it is often necessary to use reverse, which disengages the locked center diff (often causing you to get stuck) and then not allowing you to go forward again to relock the center diff. This was my motivation to do the mod and I would not be happy with the truck without it. There is a reason Toyota made this same change to the '03 and later models.... because it is necessary!

If your on the fence, do it.... you will be amazed at the difference... and enjoy!
 

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I have ARB, with ARB on and center locked that truck will crawl over anything it can clear. Never hear A-trac with ARB on and the center locked. The sound of A-Trac scares my girlfriend. :eek:

I agree the lock/unlock based on AT shift lever is crazy. When I'm on the side of a hill locked up, I can't get out to help someone else without unlocking. The damn thing won't lock again when I'm going up hill under load unless I blip the thottle.

I'm going to modify the center lock circuit in Oct when I can get some quality garage time. I'm considering doing the mod for locking in 4L only. I've never even thought about locking in 4H.


When have y'all used/needed 4H with locked center?
 

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Discussion Starter #16
Hey Motile! Honestly, I did it the 4Hi mod because I figured out how and I found a cool switch that fit nice. Motile helped me get started with the 4Lo lock, then I took it further with his help and drawings he provided. Since then I found it it great on fast gravel roads to keep the A-Trac from activating, now I seem to simply use it offroad all the time. I drive on a lot of mild 4X4 roads and lots of places I go don't need 4Lo, but could use the traction also I don't always feel like stopping to put it in Lo if I don't really need to.

In my opinion wiring it for both Hi and Lo is the way to go :first:
 

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I wired mine to only activate in 4L because I was being conservative... basically because the factory set-up only allowed the center dif to lock in 4L. I did not want to lock the center dif in 4H if the truck was not designed to handle that. Then I learned that the '03 has the ability to lock the center dif in either 4H or 4L so it probably wouldn't have mattered.

RogueRider, to answer your question, I have never felt that I needed the center dif lock in 4H... and I do rally slide the truck at high speeds on smooth dirt/gravel roads with absolute total control (4H with VSC OFF... and limit speeds to <75mph. If >75mph then 2wd with brake fluid level sensor disconnected). BUT, knowing what I know now, if I were to wire the mod today I would wire the mod to work in both 4H and 4L... why not? The difference the mod makes in 4L is huge, and who knows... maybe it will be just as beneficial in 4H.
 

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Completed a center diff lock mode on the 01 sequoia. I used a DPDT switch. The L signal and L4 signal to the 4WD control module are switched, no diode needed. In the DPDT off position, the 4WD works like stock (center lock only in L4 with trannie in L). Switch on locks the center diff same as nem's mod. All my testing has been static in the garage. I haven't off roaded with it yet.

It bothers me that the switch can throw the transfer case into 4WD center locked from 2WD mode. I'm thining about sourcing ground from the ADD sensor switch to ground the L4 signal with the center lock switch. I'd like to make the center lock switch do nothning while in 2WD instead of going into 4H locked center. I wish I knew more about the 4WD control module output circuits to determine if connecting the ADD and L4 signals together when they're both at +12 would damage the 4WD control module. Maybe a diode between them would be sufficent protection. Any thoughts?
 

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Discussion Starter #19
I've routinely used my new switch to go straight to 4Hi, center diff locked and no problems so far.... It does seem like it locks everything all at once, front add and center diff. Not sure if there is sequence that should be followed or if it really matters? anyone??

Basically I've started throwing the switch casually at any speed whenever I feel like it, I used to turn off the stereo and fan and listen for odd noises or grinding and so far nothing, just smooth locking action and 4WD fun. I have however always and will continue to press it while traveling in a straight line, not accelerating or while stopped just in case. I am no longer concerned about it, I just consider the switch an instant "FULL TRACTION" switch that can be used anytime I need it.... Maybe I should make a nice "F.T." label for it :D
 

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This would be perfect for the beach, where I want to stay in 4H at around 25-35mph. Some places the sand is so deep that it will slow the car down to 5mph before it gets out. Is there a link to the pictures? All I'm getting is red x's.

Jake
 
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