Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock. - 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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#1 (permalink) Old 06-30-2006, 02:32 AM
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Thumbs up Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

UPDATE: Goto post #71 (found here Page 71 ) for an revise update if you don't wanna wade through all the info.

I know this topic has been discussed to death. Since many of us are new to wheelin, all of these terms can be very confusing. This info is easily located in the owner's manuel page 123-130 ish which i know most hesitated to read. I typed this out more for me to get these straighten out so I know when or when not to use them. If I misunderstood any of these concepts, then feel free to let me know. I posted this in another thread, but thought it deserved it's own.

TRAction Control system (pg 123). This is refering to TRAC. automatically helps prevent spinning of the rear wheels (2wd models) or 4 wheels (by adding brakes) when the vehicle is started or accelerated on slippery road surfaces.
Doesn't require push button activation. Works on it's own and is activated when the ignition is turned on. all FJ's have this whether 2 or 4wd model. On automatics, I am assuming this works in 2H or 4H, doesn't matter. If the system detects wheel spin, it adds brakes to increase traction.

A-TRAC is Active Traction Control system (pg 125) automatically helps prevent the spinning of 4 wheels when the vehicle is started or accelerated on slippery road surfaces. (basically same as TRAC, but only works in 4 Lo). To activated, hit the ATRAC switch, shift into Nuetral, and shift the 4x4 lever (short knob) into 4 LO. When in 4Lo, it detects wheel slippage and adds brakes accordingly to give added traction. Again, you must be in 4Lo and hit the "ATRAC" switch.

2wd models have Auto LSD (pg 127) instead of ATRAC. Automatic Limited Slip Differential uses the traction control system (TRAC) to control engine performance AND braking when one of the rear wheels begins to spin (or slip). This gives added traction to the vehicle.
Auto LSD has it's own button, found in the upper left hand corner of the buttons (found in 2wd models only). Apparrently it must be engage with the push of the "auto LSD" button when you're on a slippery surface (snow, ice, or lots o' water).
This is the 2wd's version of ATRAC found on 4wd models.

VSC (vehicle stability control) system on pg 130: integrates the control of the systems such as ABS, TRACtion control, engine control, etc to prevent the vehicle from skidding when cornering on a slippery road surface or operating steering wheel abruptly.
VSC is activated when the FJ reachs 9mph or 15km/h.
*VSC automatically turns off (VSC off light on dash comes on) when 4H/HL or 4Lo/LL is activated (AT/MT) or when the Rear Diff is locked.

Here's the conclusion....

-Both 2wd and 4wd models have VSC and TRAC. activated when FJ is started(TRAC) or when FJ reaches 9mph (VSC) and works when it's needed. No action required on your part.
-2WD models: when in snow, ice, or water, oil or anything slippery and you need a little extra traction control. Hit the Auto LSD to get added traction in the rear wheels.
-4WD models: TRAC works in 2H or 4H. when running 4 LO in slippery conditions such as snow, ice, water, oil, mud, slicks, etc. Hit ATRAC switch for added traction.

Rear Differential Lock System: for use only when wheel spinning (as oppose to wheel slipping) occurs in a ditch or on a slippery or ragged surface. Rear diff lock is effective when one of the rear wheels is spinning.
Note: use ATRAC when there is wheel slippage or partial traction.
Use RR Diff locker when there is wheel spinning or NO traction.
-Must be in LL (MT) or 4Lo (Automatics). It is also suggested that you try the LL or 4Lo 1st, it this is not enough, then activate the Rear Diff locker.
-Also mentions that a large steering effort and careful cornering is required. Means that you'll have a hard time steering, will seem very stiff.
Note: when using the rear locker the following systems do not work and their lights will come on (ABS warning light, VSC off light, and the slip indicator [ the car icon with double SS under the tires] light will ALL come on).

Well...clear as mud? Thanks for reading.

PS: going on a LONG drive tomorrow...all the way to Fresno.

Even a blind squirrel finds a nut every now and then.

Last edited by Dragon; 03-31-2007 at 09:59 PM.
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#2 (permalink) Old 06-30-2006, 08:07 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Thanks for an outstanding and extremely informative post, Tranman! You get come reputation points from me for that one!

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#3 (permalink) Old 06-30-2006, 08:14 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

U Da Man T Man!! I am sure many new to this type of vehicle will find your write-up Extremely Informative.
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#4 (permalink) Old 06-30-2006, 08:24 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

I will add my praise to the discussion, as I have been trying to do my own research and reading since I am a newb to four wheeling. One thing that confuses me in the manual is comments on the A-TRAC system. The manual begins explanation on p. 125 of the A-TRAC system, however, the best I can tell, it is still discussing the A-TRAC system when you turn the page to 126. This is where I am confused as to quote from the manual, "Leave the system on during the ordinary driving so that it can operate when needed." When I read this, it read as if it were referring to the A-TRAC system, and yet on the previous page it says to switch to four wheel low. Anyone able to clarify my confusion here?
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#5 (permalink) Old 06-30-2006, 09:16 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Thanks for the summary....but for me its information overload. WIll print it out and put in my glove box just in case I need to look up real quick....
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#6 (permalink) Old 06-30-2006, 10:28 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Thank you for a great summary!
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#7 (permalink) Old 06-30-2006, 02:21 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Yes, great summary, BUT, there's still no real significant difference in any of the control systems (diff lock excluded). TRAC, ATRAC, and VSC all use the brakes to control wheelspin. So what if one only works in 2wd and one only works in 4lo, or if you have to push a switch to make you think you're stimulating the magic traction fairies, it's still performing the same function. The only difference is the computer programming logic involved.

"TRAC - If the system detects wheel spin, it adds brakes to increase traction."
"ATRAC - detects wheel slippage and adds brakes accordingly to give added traction"
"ALSD - uses the traction control system (TRAC) to control engine performance AND braking when one of the rear wheels begins to spin (or slip). "
"VSC - prevent the vehicle from skidding when cornering on a slippery road surface or operating steering wheel abruptly"

Does anyone see any real difference here? I just want someone to admit that it is one system that performs these functions. It's all the same computer, the same abs sensors, the same brakes. The abs sensors are used to detect wheel slippage, and then the brakes are applied individually as needed. The ALSD says it also controls engine performance, though I don't see why that function would be labeled ALSD, as it really should be part of TRAC. And then VSC is to prevent doing 360s around a corner, as opposed to the other systems that are designed for assistance with forward acceleration. BUT, even the VSC is detecting a loss of traction and applying brakes to individual wheels.

"RRDIFF - for use only when wheel spinning (as oppose to wheel slipping)"
There is no difference in slipping and spinning, so long as you're referring to forward acceleration (as opposed to braking). And how could one wheel ever spin anyway, with TRAC always active?

"Hit the Auto LSD to get added traction in the rear wheels."
So the TRAC only gives you a little extra traction, but ALSD applies the brakes a little harder? I don't get it.

"Hit ATRAC switch for added traction."
Again, added traction?

I know you didn't make this stuff up Tran, I'm not blaming you, but you have to admit it's baloney. That's why you can buy a $40 ATRAC switch to "unleash" this magic. Imagine how much money they've made by getting people to buy the upgrade package just for the ATRAC.


Customer: Why do I want this package?
Dealer: It has ATRAC!
C: It has an 8-track?!
D: No, AAAAA TRAC.
C: Aww that sucks, I have some old 8 track tapes at home that would sound great on the FJammer.
D: (fake chuckle)
C: So what is ATRAC?
D: It's a traction control system that controls wheel slippage in adverse conditions.
C: Oh. Doesn't it already have that standard?
D: No. That's TRAC.
C: So what's the difference?
D: Well, that's TRAC, this is AAAAA TRAC!
C: So the A makes it better?
D: Well it's more than just an A sir. See, it controls the wheel spin when you're in the 4wd low gear.
C: And TRAC doesn't do that?
D: Well it does, but it's different.
C: How?
D: Well, ATRAC only works in 4lo.
C: And TRAC doesn't?
D: Yes TRAC works all the time.
C: So TRAC also works in 4lo.
D: Well yes.
C: So why do I want ATRAC?
D: Because it's better.
C: And you can only get ATRAC in the 4wd? What if I wanted 2wd?
D: Well you can get Auto LSD.
C: 8 tracks, LSD, what's going on here?
D: (another fake chuckle) Not that kind of LSD sir. It stands for Limited Slip Differential.
C: What's that?
D: It's actually a simulated LSD, it uses the brakes to control wheel spin.
C: I thought that's what TRAC does.
D: It does, but TRAC is on all the time. You have to push a button to use ALSD.
C: Hmm. You people are proud of your buttons aren't you. So back to the ATRAC, how do I turn it on?
D: You push this little button right here.
C: And how can I tell it's working?
D: There's a light on the button.
C: Oh, a light. Well that's pretty cool. Alright, I'll take it. And how much extra is this package?
D: It's just a little bit more, we'll make the numbers work. Let's go sign those papers... (as they walk off into the sunset)
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#8 (permalink) Old 06-30-2006, 11:11 PM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Thanks for the responses and reputation points. Just wanted all to know that tho I post frequently, I am not a wheeler. I have very little experience when it comes to this off roadin stuff. I learning just like the rest of us. I plan on doing light trails and progressing slowly. Haven't even used some of these systems yet.

Quote:
Ridge111 previously said:
I know you didn't make this stuff up Tran, I'm not blaming you, but you have to admit it's baloney. That's why you can buy a $40 ATRAC switch to "unleash" this magic. Imagine how much money they've made by getting people to buy the upgrade package just for the ATRAC.
You're right, I didn't make it up. Just what I gathered from reading and just tried to make some sense of it myself. I could be totally wrong. I haven't used any of these systems in real world applications other than playing with them briefly.
Just thought I would shared my interpretation of the material.

Hear ya on the atrac switch as well. I would say most who got the package probably wanted the other items too. Just imagine dealerships also made $4K plus on each of just who bought at MSRP!

Quote:
Ridge111 previously said:
Yes, great summary, BUT, there's still no real significant difference in any of the control systems (diff lock excluded). TRAC, ATRAC, and VSC all use the brakes to control wheelspin. So what if one only works in 2wd and one only works in 4lo, or if you have to push a switch to make you think you're stimulating the magic traction fairies, it's still performing the same function. The only difference is the computer programming logic involved.

"TRAC - If the system detects wheel spin, it adds brakes to increase traction."
"ATRAC - detects wheel slippage and adds brakes accordingly to give added traction"
"ALSD - uses the traction control system (TRAC) to control engine performance AND braking when one of the rear wheels begins to spin (or slip). "
"VSC - prevent the vehicle from skidding when cornering on a slippery road surface or operating steering wheel abruptly"
I agree with you. when I first read it, I thought all were the same, especially TRAC and VSC. I bet some of the more techinically minded members know the differences and the exact applications. (RoverGGM, KLD, Percy, Thai, there's more of you out there, please chime in)

Ridge, by added traction, I meant added torque not added braking. I don't fully understand these issues myself so I can't competently and completely answer your questions.

Sounds like the difference b/t TRAC and ATRAC is not much. One works for normal driving and one for 4LO. Same system, slightly different application.
Sounds like ASLD is similar to ATRAC except it is for 2WD models and only works in the rear wheels. It is probably the same, but again works only in the rear wheels. VSC incorporates ABS, traction control, and manipulates engine performace to give your more control of the vehicles for turning. A different application than TRAC, ALSD, or ATRAC - all for wheel slippage.

The real world difference b/t TRAC and ATRAC. All I can say is go out and get yourself stuck and see if ATRAC makes a difference over TRAC or not. Some say it does make a BIG difference. I think when you are in 4Lo, TRAC is not active. I'm not 100% about this one tho. If that is true, then ATRAC (in 4 LO) would replace TRAC. Why didn't they just make it automatic instead of us having to depress a switch?

I'm guessing b/c sometimes you want RR diff lock and sometimes you want ATRAC (again different applications). You can't run them both at the same time. Why? I don't know but this one's been hotly debated again and again.
Anyways if you find the answers, post them up. I'd like to know as well. Cheers, Tran

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#9 (permalink) Old 07-01-2006, 01:04 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Although these systems use the same basic components, they use different parameters and sensors to affect their function. For example, VSC uses a yaw sensor to detect angular momentum to calculate which brakes to apply and what direction the skid is likely to occur. The speed they come into play is different, as you wont be going more than 10-15 mph in 4lo, while you could be at freeway speeds in 2hi. Hope that helps...

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#10 (permalink) Old 07-01-2006, 08:37 AM
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Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

I know that the manual says to reduce speed to 50mph to shift from 2H to 4H (in automatics), but if you are driving in wet or snowy conditions on a highway is there limit to "safe" speed in 4H mode. Obviously, the conditions of the road stipulate to a great extent what is a safe speed, but what is safe for the 4H operation of the engine. The other night when driving home, we ran into a heavy downpour with puddling on the highway, and I was concerned about how fast I should/could go with 4H active?
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