The "No Cut" A-TRAC + RR DIFF Hack. - Toyota FJ Cruiser Forum
Transmissions / Transfer Cases / Traction Aids This area is for discussion, questions and problems with the FJ Cruiser's gear train, including topics on A-TRAC, VSC, locking diffs, gear ratios, manual vs. AT, etc.

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post #1 of 275 (permalink) Old 12-20-2006, 01:47 PM Thread Starter
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The "No Cut" A-TRAC + RR DIFF Hack - UPDATED!.

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

https://www.fjcruiserforums.com/forum...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:



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:



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.

Last edited by superstar555; 02-14-2007 at 10:35 AM.
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post #2 of 275 (permalink) Old 12-20-2006, 01:57 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Thanks a bunch!
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post #3 of 275 (permalink) Old 12-20-2006, 02:12 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Quote:
superstar555 previously said: View Post

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.
So I'll need to connect connectors back after taping over Pin 11?

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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:




And then run it to a fused, switched, +12v source:
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?
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Last edited by DFrelich; 12-20-2006 at 02:15 PM.
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post #4 of 275 (permalink) Old 12-20-2006, 02:17 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Great work! Gotta love ingenuity...

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post #5 of 275 (permalink) Old 12-20-2006, 02:18 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

That is the reason I am hooked on this forum.....
I just gave you a rep. point (I think).

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post #6 of 275 (permalink) Old 12-20-2006, 02:18 PM Thread Starter
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Quote:
DFrelich previously said: View Post
So I'll need to connect connectors back after taping over Pin 11?



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?
Updated to reflect answers to these questions.

Thanks.
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post #7 of 275 (permalink) Old 12-20-2006, 02:25 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Thanx for the great info. I have another mod for the Holidays
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post #8 of 275 (permalink) Old 12-20-2006, 02:27 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Rep for you. Thanks for taking the time to distill this hack/mod down to the bare essentials.

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post #9 of 275 (permalink) Old 12-20-2006, 02:29 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Quote:
superstar555 previously said: View Post
.....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).
I think that was me asking...I support you !! go for it!!!!
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post #10 of 275 (permalink) Old 12-20-2006, 02:37 PM
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Re: The "No Cut" A-TRAC + RR DIFF Hack.

Outstanding write up, thanks.

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