A-TRAC/TRAC/AUTO LSD Explained (Easy to understand, I hope!)

De nada amigo... I just hope it helps!

To me, in 4WD, having the stronger traction control makes sense.

In H4 you want TRAC OFF MODE (this is standard, but called TRAC ON MODE in 2009-2011, but requires a button push after 2011). The "OFF" on 2012+ models means engine regulation is off.

In L4 you want A-TRAC, push button the first time you use L4, and it will always be on standby for if and when the tires spin.

 

So if I am in 4H and turn Trac off (hold the button for 3-5 sec), do I have any form of LSD? I guess I am looking for a yes or no answer.....

 

When you hold the button down for 3+ seconds (while stopped) it is VSC OFF, not Trac Off. But, as Rock Lobster said, that in a "no".

TRAC OFF is when you hit the button quickly (moving or stopped) and that is a higher degree of limited slip: TRAC with engine regulation OFF. This applies to all Tacomas in 2WD since 2009, and all 4WD Tacomas in H4 since 2012. (2009-2011 is in this mode in H4, without any button pushing, and it was called TRAC then)

 

I am very new to 4 wheel drive trucks, just bought a 2013 SR5 4 wheel drive. I do not have A-TRAC. When I quick push the VSC button I get the AUTO LSD and the truck swerving light. I assume this is TRAC? When I long push the VSC button I get TRAC off and the truck swerving light. My question is what are the levels of traction that I should go with? From lightest duty to heavy duty. Thank you all so much for the help, I hope to be getting out into the woods soon to see what my truck can do.

 

Hi and welcome to Toyota Four Wheeling!

You have 2WD High (H2), 4WD High (H4), and 4WD Low (L4) to begin with.

The truck in H2 and H4 is normally in TRAC MODE (a light limited slip). There is engine output regulation and some braking of a spinning tire so drive force goes to the traction tire.

A quick press of the VSC button puts you into AUTO LSD in H2 and TRAC OFF in H4 and they are a stronger limited slip, both are essentially the same function but with different names, ie. limited slip without any engine output regulation. So full engine drive power with braking of a spinning tire.

In H2 and H4: if you stop driving and hold down the VSC button for a few seconds then you have VSC OFF MODE, which is no traction control and no stability control... essentially old fashion open differentials.

In L4, there is no choices for non-Off Road Tacomas other than doing the 4 Lo Trac Mod (Yellow Wire Mod)... this fools the system into thinking it is in H4 (TRAC OFF MODE) while it is in L4.

So from lightest duty to heaviest:

2WD VSC OFF
2WD TRAC
2WD AUTO LSD
4WD HIGH VSC OFF
4WD HIGH TRAC
4WD HIGH TRAC OFF

(I never have any reason for VSC OFF, never... it may be desirable in snow to spin clean a tire?)

4WD LOW (without the mod) may be less traction than 4WD HIGH TRAC OFF depending on the driving surface. I could climb higher in H4 TRAC OFF than in Low Range (without A-TRAC or the locker). Spinning tires does not move you, it only digs you in deeper. L4 give you more crawling/ pulling power as long as there is no tire spin.

Don't forget that letting air out of the tires could be the biggest help in moving the truck in poor traction situations.

 

Thank you so much David K. This helps me a lot. I hope to be doing some trails this weekend. I hope I'll have to use the 4 wheel drive.

 

So I played around with this a bit on my new 2015 TRD Sport. Pressing the VSC button in 2wd illuminates the VSC off light (the "skidding truck" light) and the "Auto LSD" light combined. Pressing and holding the VSC button results in "TRAC off" and the VSC off light, which I assume means open rear diff, no throttle intervention. In 4wd, pressing the VSC button gives me "TRAC off" again, and no other changes.

So what is the "VSC off"+"Auto LSD" giving me in 2wd?

BTW, I'm only talking about H4. Not messing with L4 at all yet.

Edited because I had to correct a couple statements. Edited again for more corrections.

 

Wish I had read this closer earlier. It answers several of my questions. But a couple of things still throw me. So, in H2, pressing VSC off illuminates the "skidding truck off" light, turns off the throttle intervention, so it is pure Auto LSD. Holding VSC off in H2 illuminates "TRAC off," and now you're pure open-diff rear. In H4, pressing VSC off illuminates "TRAC off" again, but now, instead of open diffs, you're "strong" limited slip both front and rear, because of no throttle intervention, but braking limited slip? So you need to slow way down or stop, and then holding the VSC off button puts you into VSC off, with the skidding truck light, and now you're open diffs front and rear? Did I get all that right? I mean, you have that typed in the quote, essentially, but it seems the meaning of the "TRAC off" light is opposite between H2 and H4.

BTW, thanks Rock Lobster. Sounds like Toyota changes the way their buttons operate, and the meaning of the lights, from year to year, or even 4wd-mode to 4wd-mode.

I played in the snow a little, on the slick roads, not deep snow. Between standard H2 and "VSC off/Auto LSD," the truck behaved better under heavy throttle in regular H2. With VSC off, it would break loose and the rear would slip a little sideways, kinda like my Wrangler with the TRAC-Lok rear, which makes it quite squirrelly in 2wd. In normal H2, you could feel a wheel spin, but it wouldn't skid sideways. I didn't play in "TRAC off" in H2 at all, figuring no throttle intervention and no limited slip would be a bad combination on slick roads.

 

I think I'll never understand this.

 

So there is a hardware difference between TRAC and A-TRAC? Until I read this, I thought A-TRAC was just TRAC for L4.

 

Heresy

 

Well, I'm working my way through this thread, trying to figure it all out. I started at the front, then tried to skip ahead to the 2013+ time frame since it quickly became apparent that the 2009-2010 systems were a bit different from the 2015. Can you give me a hint approximately where I might find that hardware difference between TRAC and A-TRAC?

 

This thread explained the post 2012 changes pretty well... Although this thread here is better comprehensively, I think. But maybe I'm just reading too much and getting it all confused. What the heck is "VSC" and what is its purpose? Other than to confuse matters? Is it throttle intervention? Brake intervention? Both? Based on wheel spin? Lateral acceleration with steering angle?

VSC on in H2 (no buttons pressed or held), you have brake and throttle intervention. VSC off in H2, you only have brake intervention. TRAC off in H2, you have no intervention, open diffs.

In H4, no buttons pressed, you have brake and throttle intervention. Press, you get TRAC off (no throttle intervention, only brake intervention). Hold, you get VSC off (no brake intervention, no throttle intervention, open diffs).

So the meaning of the lights/icons change depending on whether you're in H2 or H4?

My Tacoma seems to be a great truck, but DANG, this is confusing!

 

Ok, I'm sorry, I think I finally had an epiphany moment, with this post. It finally made sense, for this TRD Sport driver (why, oh why, did Toyota not offer the A-TRAC, at least, in the DCLB?! But I digress...). Bottom line: in H2, if you want to turn off throttle intervention (only), momentarily press the VSC button. If you want to turn off brake AND throttle intervention, hold the VSC button. Quick press gives you maximum traction, press and hold gives you minimum traction. Got it. Works for me. Now I just need to get an off-road Tacoma, somehow. But how????

BTW, David K, indispensable information in this and the other two threads I ran across on this subject. Thank you.

 

Hi Dogboy, I am sorry I didn't see this until it looks like you figured it out.

In case you didn't or others want to see my way of explaining it...

1) Quick Press moving or not activates TRAC OFF (which IS TRAC but the engine regulation is OFF). This is also called AUTO LSD in 2WD only (VSC is off to 30 mph then comes on). In 4WD HI from 2009-2011 it was called TRAC, but with regulation off normally, no button push.
In 2012, they added a button push for TRAC OFF and made TRAC have regulation as the standard H4 mode.

2) Stop Moving, press and hold in the button in H2 or H4 for a few seconds to get VSC OFF MODE (no TRAC no TRAC OFF, no VSC, nothing... just open spinning differentials and tires. However, there is a hidden genie (lawyer?) who will cut in if he thinks you are about to wreck and he turns on VSC to save you. I find NO ADVANTAGE to VSC OFF... it's the same as my 2005 Tacoma with no traction control or limited slip.

3) In LOW RANGE 4WD (L4), only the OFF ROAD has traction systems beyond the low gears: Rear Locker and A-TRAC. A-TRAC needs the hydraulic brake booster and only the 4WD OFF ROADS have it (since 2009) to provide the locker-like, tire rotation matching ability of A-TRAC on ALL 4 tires!

MOD for non Off Road Tacomas with 4WD: 4 LO TRAC MOD (yellow wire mod) fools the truck into thinking in is in H4 when in L4 so you have the advantage of TRAC (TRAC OFF) limited slip on all 4 tires, while in low range.

Traction control, while many poo poo it, it obviously works over open differentials and those non Off Road TRD Tacomans who have done the mod swear by the advantages it gives to have TRAC in low range.

TRAC is NOT A-TRAC... There is a lot of spin in TRAC before it fully engages, whereas when A-TRAC is 'active' the tires do not spin and are locked together any time one is in the air, or looses traction and begins to spin... call it 'automatic lockers'... some spin but stops it to move you ahead when traction is lost... and no problem steering, as lockers cause.

TRAC is great when you are moving and A-TRAC is great when you are crawling.

As for why Toyota only makes a standard bed Off Road double cab (A-TRAC/ rear locker) truck? Long beds are just too long for the kind of trails the Tacoma Off Road was made for, and if long beds had A-TRAC, people would go crazy taking their trucks to the extreme and getting hung up being so long... maybe? I do get that having these systems could prevent long beds from getting stuck in other conditions. I think it is a crime that Canadians can't get a double cab OFF ROAD, just the Access Cab.

 

The 6' bed is the standard bed , seeing how all Tacoma models except the DCSB have it

 

Yes , exactly , the 6' bed length is the standard bed length on Tacomas , the double cabs with 5' beds are called " short beds " . There is no shorter bed on any Tacoma .

 

I have really enjoyed reading the posts by the two of you as I've researched these traction control systems on here. Two invaluable contributors, that seem to say the same thing in different ways, that allowed me to finally sorta figure the systems out.

I sure do wish that at least A-TRAC was available on the DCLB, or DCS(tandard)B, however you want to term it (the 6' bed). I think I already said that, though, at least once. I probably will never need it, because I don't do extreme wheeling. But it would be better to have and not need, than need and not have.

 

Double-cab options from the Toyota website. The DCLB 4x4 is cut off to the right, but you get the idea:

 

Short Bed

There it is