Easy hack for Active TRAC

[Alex H]

I don't have a copy of the wiring diagram and need to know where the connector "LA2" is located.

Is it the second big blue connector from the (bottom or top) in side the left kick panel ?

Thanks

LA2 is the white 11 pin connector on the top row of 2 connectors in the left kick panel. It will be the left of the pair . Pin 11 will be in a corner of the connector away from the thumb tab that releases the connector, the wire will be light blue with a yellow tracer.

If you post a picture I can tell you if it is the right one.

 

[Alex H]

Sorry Mike, my previous reply incorrectly stated LA2 is the left of the upper pair of connectors. It is in fact, the right-hand one.

 

[freewheeling frank]

more, more!! Did it work?

Alex, what you are saying is that once you set the jumper wire, pump the brakes, etc, then you can remove the jumper wire and put everything back the way it was? And run the ATRAC and locker together?


Oh, wwops. This is to clear the possible error code.

 

[freewheeling frank]

Ok, is there a way for me to pull the pin out of the connector without special tools? Would rather not cut the wire. I have located the connector and pulled it. Found the right wire.

But it seems I should be able to pull the pin.

 

[ickmann]

Thank God we're not talkin' about IEDs or grenades here !!


"But it seems I should be able to pull the pin"

ick

 

[Alex H]

Frank, before you pull the pin you must pop up the secondary lock like this:

There is a special tool but you can use a sharp steel pick. Don't pull it all of the way out, just lift up as much as is shown. Then you can go to the front of the connector and lift up on the pin retainer while tugging on the wire. Tape up the pin and tuck it out of the way.

 

[freewheeling frank]

I did figure out how to get that part pried up before. But I still can't get the pin out. What exactly do you mean by "lift up on the pin retainer".

I am trying to do this without wrecking anything, but eventually I will start yanking on it pretty good.

 

[Alex H]

Lift up on the part indicated by the arrow while you tug on the wire. A sharp steel pick will work, a sewing needle will also do in a pinch. Paper clips are too flexible to do the job.

 

[freewheeling frank]

Yeah, I got it figured out today. Ground down a horseshoe nail.

Now I get the VSC light, ABS light, and i think the TRAC light all the time. TRAC light I think is the pic of the swerving tracks and vehicle? Doesn't matter if I am in 2wd, 4h, or 4l. Can't get the ATRAC light no matter what I do. ABS and traction control definitely are not working in 2WD.

It seems to act like it thinks the rear is locked all the time. The rear locker indicator works normally. Blinks when you first press the switch, then goes solid once you move a bit in 4Low.


So it doesn't seem to have worked like we hoped. or if it did, it isn't worth giving up ABS in 2WD to get it.

Any ideas, Alex? I am willing to try other ideas.

 

[Alex H]

Let's see what codes you have. Check codes this way:

Start with key off.
Locate the 16 pin DLC3 under the left side of the dashboard.
It has 2 rows of 8 terminals, one above the other.
With a jumper wire, connect terminals TC and CG of DLC3.
CG is the 4th pin from the left, top row.
TC is the 5th pin from the left, bottom row.
Turn key on.
Read the 2-digit codes given by the ABS light and the VSC/TRAC warning lights.

Code C1248 will be a 48 by that method. What codes do you get from which lights?

 

[freewheeling frank]

alright, I will work on that. Got to finish making dinner, then I will take a look.


If I hvae the C1248 code, and I clear it per your previous instructions, think I might get what we are looking for?

 

[freewheeling frank]

I found DLC3, or I think I did. But in order to jump those terminals I am going to have to pull the lower dashboard. And I am having trouble doing that and its getting dark.

I will have to look at it again tomorrow.

 

[Alex H]

Frank, let's see what codes you have first. You shouldn't have to disassemble anything to access DLC3. It should look something like this:

Just to verify, you pulled the light blue/yellow wire out of connector LA2, the upper righthand connector in the mass in the left kick panel?

If you put the wire back and clear the codes per my previous instructions do the lights go out?

 

[freewheeling frank]

Ok, I was looking at the wrong thing.

I have to run into town so I put the pin back in and everything seems normal now. I will look at it again.

 

[L8Apex]

I want to see this A-TRAC/RearLocker combo idea proven, but it looks like we've hit a snag since it doesn't work to simply disconnect the signal wire for the rear diff status. So here's my suggestion:

With the wiring in place, use a voltmeter to check the voltage on the rear diff status wire. Check voltage with the rear diff locked, and unlocked. I'm guessing that it's grounded (0V) when locked, and 12V when unlocked. Or it could be the other way around. Either way, once you figure out what voltage is supposed to be seen on the wire when the diff is unlocked, simply cut the wire (remove the pin) and either ground it or supply the appropriate voltage on the ECU side.

 

[BigBlue]

Has anyone been successful with this yet?????

 

[L8Apex]

I'm still waiting for an answer too. In the meantime, I've done some more research about it.

After looking through the factory service manual, it seems that I was correct in my previous post: When the rear diff is UNLOCKED, there should be VOLTAGE on the wire.

According to the FSM, the "rear diff lock position" wire is at pin 26 on the skid control ECU connector. The ECU looks for voltage on this wire as follows:

Ignition on, Rear diff locked: "below 1.5V"
Ignition on, Rear diff unlocked: "between 8V and 14V"

So you need to supply voltage on this wire to trick the ECU into thinking the rear diff is unlocked. And then you'll be able to use A-TRAC with the rear diff locked.

Note: This hack could potentially allow VSC/ABS/TRAC to be active while the rear diff is locked. This would be bad. VSC needs to control individual wheel speed to adjust vehicle heading in a skid. A locked diff would really mess with it. If you hack it, be sure to unlock the diff before shifting into 2WD.

If you're creative with the wiring, the hack could only be enabled when in low range. (the 4L indicator signal is on pin 21.) VSC is already disabled in low range anyway.

I really don't have time to test this out myself. I barely see the FJC these days since it's my wife's daily driver. But I'm more than happy to dig through the FSM and EWD and give my suggestions.

 

[Alex H]

After looking through the factory service manual, it seems that I was correct in my previous post: When the rear diff is UNLOCKED, there should be VOLTAGE on the wire.

Yes! I took a look at the wiring diagram on page BC-111 of the service manual and you are exactly right. I incorrectly assumed the Skid Control ECU supplied the signal voltage to the switch, the signal voltage actually comes through the rear diff lock indicator LED in the combination meter.

A possible way of making this work is to disconnect the light blue/yellow wire at LA2 and put a jumper wire at the Skid Control ECU (master cylinder and pump) between connector A4, pin 26 (light blue/yellow wire) and Connector A5, pin 1 (black/orange wire).

There are several ways of making this work, the key is to disconnect the Skid Control ECU from the rear diff indicator LED/switch circuit and supply battery voltage to the Skid Control ECU at connector A5, pin 1 when the ignition is on.

 

[ShottsUZJ100]

This is not an experiment I would try.
Engage the locker, and apply brakes to one side?
I can hear axle shafts snapping from here.


By all means, try it on your truck tho, and report back

This is not the case as proven since 2000 in the UZJ100. Locked, no slip between sides can be detected and therefore no TRAC-braking is applied to that axle.

 

[ShottsUZJ100]

for the A-TRAC system to totally ignore (both) rear-wheels I think that there would have to be 2 separate A-TRAC systems; one monitoring the front wheels and one monitoring the rear wheels.

Front A-TRAC - ignores rear wheel slippage
Rear A-TRAC - ignores front sheel slippage
?

That is correct. Each axle is handled on it's own. Your CDL is locked.