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The "No Cut" A-TRAC + RR DIFF Hack.

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187K views 290 replies 135 participants last post by  Ridem32  
#1 · (Edited)
The "No Cut" A-TRAC + RR DIFF Hack - UPDATED!.

I have received several requests to take the combined knowledge of my original post:

http://www.fjcruiserforums.com/foru...ums.com/forums/4x4-off-road-tech/16349-re-examining-trac-rr-diff-lock-hack.html

and place it in a seperate, and more easily read format. Original credit for the ECU hack goes to Alex, credit for the photos goes to SwissArmySUV.

This procedure was changed on 12/28 to remove the need for a wire tap. Some inline pictures were hyperlinked due to size.

PROBLEM: Early production 2007 model FJs (~pre-November 2006) do not allow A-TRAC to operate in conjunction with the Rear Differential Locker (RR DIFF LOCK) or vice-versa. The ECU allows only one or the other to be active, but not both.

WORKAROUND: Alex discovered a way to "fool" the ECU into thinking that the RR DIFF LOCK was always inactive by cutting the RR DIFF status wire coming from the rear, and applying +12v to it as it entered the ECU. From the ECUs perspective, +12v on this wire indicates that the RR DIFF is off. Since the ECU thinks the RR DIFF LOCK is off, it has no issues allowing A-TRAC to engage. Personally, I had issues cutting ANY wire on a factory wiring harness, much less one that is under the hood (exposed to elements) and connects to an ECU, so I looked for a different way.

SOLUTION After perusing the factory wiring diagram, I was able to track down the connector in which the RR DIFF signal joins the main engine compartment wiring harness. I surmised that by isolating this RR DIFF LOCK signal BEFORE it entered the engine compartment, I would be able to avoid cutting it at all. Subsequent testing has proven my theory, and I have modified 4 FJs (including my own) since then without cutting a single wire, or modifying the FJ in any way that is not 100% reversible. This modification is not difficult in the least, but DOES take a bit longer to accomplish than the Alex mod. Personally, I am able to complete it in less than 30 minutes, and for me, the extra effort is worth it for the benefits mentioned above.

THE MOD

Before we begin, here are the tools that are required:

http://the895.org/uploader1/uploaded/tools.jpg

Let's get a good look at the connector we will be utilizing:

Image


Pay close attention to Pin 11. That is the ONLY pin we are concerned with.

Step #1: To get access to this connector, you must remove the driver's side the dead pedal, sill panel, and the driver's side kick panel. Location of LA2 is noted below:

Image


Step #2: Once you have access to LA2, disconnect the battery (for safety), unplug the LA2 connector by pressing the white tab on the "passenger" side of the plug and gently pulling. Don't pull on the wires, pull on the plug itself.

Once you have the female plug out, you will need to remove the male side of the plug. This is held in by a small tab on the left side of the blue plug holder. Insert a wide blade screwdriver to dislodge the latch, and then gently push the "male" side of the connector out of the blue retaining structure (towards the firewall). You should now have the male side free:

http://the895.org/uploader1/uploaded/conn-front.jpg

Now that the "male" side of the connector is free, find pin 11 (it is blue with a yellow stripe). Once you know which wire you need, gently pry up the primary retainer mechanism on the top of the plug:

http://the895.org/uploader1/uploaded/conn-back2.jpg

Once this is lifted, insert a small, thin, flat blade screwdriver in from the wire side of the connector, in-between the wire and the top of the connector. This should disengage the secondary retaining latch holding the wire in. Pull the pin out of the connector. It should come out easily.

http://the895.org/uploader1/uploaded/pinout.jpg

Once the pin is out of the connector, go ahead and reconnect LA2. No tape or other isolation is required.

Take the newly freed pin and connect a length of wire to it. If you happen to have a female spade connector the right size, use it. If not, just wrap the wire around the pin several times to ensure a good connection. This is a low current application.

http://the895.org/uploader1/uploaded/wireattached.jpg


Now, tape up the connection.

http://the895.org/uploader1/uploaded/taped.jpg


Personally, I did not want to use heat-shrink tubing alone as it can be a PITA to remove later, so I taped first, and then used some tubing without shrinking it down all the way. Just enough to help hold things together.

http://the895.org/uploader1/uploaded/tubed.jpg

Now, connect the other end of the wire to a +12V switched source:

http://the895.org/uploader1/uploaded/fusebox.jpg

Before re-assembling the trim pieces, now is a good time to make sure everything is connected properly. Turn on the truck, shift into L (1st), 4LO, and turn on RR DIFF LOCK and A-TRAC in no particular order, If everything is right you should see this:

http://the895.org/uploader1/uploaded/success.jpg


If Toyota ever decides to retro-fit pre-November FJ's, just un-tape the pin, and reverse this procedure.


FAQ UPDATE 2/14/2007

"I accidentally connected the +12v wire to the wrong side of the circuit. Now my truck will not start"

Correct the hack, and check the 10A IGN fuse in the drivers side fuse panel. If blown (it is), replace it.
 
D
#3 · (Edited)
superstar555 said:
Step #2: Once you have access to LA2, unplug the connector and place a SMALL bit of non-conductive material over the male side of LA2:pin 11. Through trial and error, I have found that a SMALL rectangle of electrical tape pressed over the male pin isolates the pin from the connector nicely. For the truly anal, removing this pin from the connector is a possible, yet difficult, alternative.
Click to expand...
So I'll need to connect connectors back after taping over Pin 11?

superstar555 said:
Step #3: Now that the ECU can't see the true state of the RR DIFF LOCK signal, we need to ensure that it always thinks the RR DIFF LOCK is off. To do this we need to supply +12v to the female side of LA2:pin 11. The simplest way to do so is to purchace an inline tap, place it on the female side of LA2:pin 11:

Image



And then run it to a fused, switched, +12v source:
Click to expand...
I want to be sure. Only the blue wire in your picture. Ignore the red one because it is feeding power source to something else?
 
#9 ·
superstar555 said:
.....My truck didn't come with a locking rear diff (RR DIFF LOCK) or A-TRAC, will this mod enable A-TRAC?[/i]

No. You must already have A-TRAC enabled, and a RR DIFF LOCK for this mod to be effective.

(I will update the FAQ as issues arise).
Click to expand...
I think that was me asking...I support you !! go for it!!!! :clap:
 
#10 ·
Outstanding write up, thanks.
 
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#12 ·
Superstar555,

Thanks for the post. If Toyota doesn't come through with an update for those of us who made our purchase pre November, I will try this mod. I called Toyota today and ledged my complant but got the same old bull of it can't be done and no plans to rectify the situation. I also called my dealer with same and explained that I didn't find this to be fair to those who jumped in early to give this new vehicle a try at the sticker price plus tax. Since this is my fifth Toyota from them, I told him that I was going to trade it in on a H1 Hummer. Just kidding but left it that way with him.

Thanks again!!!
 
S
#13 ·
I read on another post the jumpering 4 to 11 was no longer a good idea because that did not provide a CONSTANT 12v source. Is that correct?

I am guessing that to be true and you are getting around that by adding the inline t-tap connector and connecting it directly to the fuse box. That sounds good, but I am worried after that is done it can never be returned to truly stock. If you remove the t-tap in the future the wire will be broken and if you leave it in place then it will be "evidence".

Did I get this right? I will probably still do the hack in the kick panel instead of under the hood, but I just wanted to be sure I understand everything first.

Thanks alot for your hard work on this.

Shannon
 
#17 ·
Correct. Pin 4 was left out on purpose due to issues on some FJs.

A good tap will not cut the wire, but will make contact by cutting thru the insulation of wire.

I hate wire taps with a passion, but in a low-amperage, weather-protected situation like this, it's the easiest tool for the job.
 
B
#14 ·
Thanks Superstar. You're a....ummmm Superstar! :rofl:
 
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#19 ·
With the "cut" method, you are actually cutting a wire in the factory wiring harness, and stripping back a (small) bit of insulation on another via the use of a wire tap. These wires are located under the hood and are exposed to the elements.

The "no cut" method described above cuts no wires, and is done inside the cabin of the vehicle where it is protected from the elements.

They both accomplish the exact same thing.
 
#25 ·
I put this is my bookmarks, if any of u local guys in "THE Valley" can help me do this in person, Ill give you a 6pack or a free air hose, IM me. Nice find rep points on this thread.
 
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#39 ·
Chats, I'm in no hurry to do this but would like to do this hack. Let's see if we can't get a group of guys together and order a bunch of the T-taps and have a "superstar No cut Hack". I bet the next time you go wheelin with a group of FJ's, you're bound to run into someone who has done the hack. Just have the T-tap ready and the instructions and you can do it on the trail.

Superstar, BIG thanks for the dummies version. Nice contribution man. Should we call this the Superstar No Cut Atrac/Locker Hack or simply the No Cut Atrac/Locker Hack?
 
#26 ·
A few things still need to be addressed here, not all are super wizz bangs at electrical things.

1. What size is that blue wire you are using.
2. What size wire tap?
 
#27 ·
1) The size of the wire used to route power from the fuse box isn't really critical. There is no current to speak of in this circuit so 22ga would be fine. Even smaller would be probably be OK if that is what you have lying around.

2) I do not have the box that my T-Splices came in, but I would guess that they are of the "18-22ga" variety.
 
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