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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.

1,628 Posts
Discussion Starter · #2 ·
Re: Making sense of TRAC, Auto LSD, ATRAC, VSC, & Rear Diff lock.

Wow! I just reread this thread and relearned some things. A BIG thanks to Thai, KLD, and others for helping to clarify these electronic doo-dads we have on our FJ's.

Just a quick review of what was originally posted plus notes from KLD, Thai, CruiserLarry, & Others.

Trac : Traction control. All FJ's have this, both 2WD & 4WD. Works automatically when ignition is started (no push button needed). Works by applying brakes and controls (decreases) engine throttle to give added traction to varying wheels when system detects wheel slippage/spinning ("think spinning your wheels on ice"). Works all the time in 2WD and in 2H & 4H (AT) or HL (MT). This system basically helps to maintain traction in slippery conditions such as wet/icy for forward movement by applying brakes and controlling engine throttle to regain/maintain traction as a safety feature.
TRAC is disabled in 4LO. Again, you don't want this system to control engine power when you are climbing obstacles.

ATRAC : More aggressive form of TRAC & for 4WD OFF ROAD use only. Does the same thing as TRAC except it doesn't cut/control engine throttle. Instead, it transfers torque from slipping/spinning wheel(s) to non slipping wheel. This gives added traction & forward momentum to overcome Off-road obstacles. This can only be engaged while in 4LO (AT) or LL (MT) and by pressing the "ATRAC" switch.
Also, only 4WD models with the Rear Diff Locker have ATRAC capability. Even then, you need the $50 ATRAC switch installed to use this system if you didn't purchase either Upgrade Pkgs with your FJ (UP or UR).
*AT: to go into 4Lo, stop, put into Nuetral, then shift into 4Lo (short knob).
MT: refer to manual, sorry I have the AT.

Auto LSD: found on 2WD models. Similar to ATRAC for 4WD. Must press the Auto LSD button/switch to activate it.

VSC (vehicle stability control) : integrates ABS, TRACtion control, engine control, etc to prevent the vehicle from skidding when cornering. Prevents oversteering or understeering & will save your ass if your car loses control (Thai). Detects angular momentum and tries to control direction of skid. VSC is automatically activated when the FJ reachs 9mph or 15km/h.
*VSC automatically turns itself 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. VSC is for preventing rollovers at high speeds thus not used while wheelin' in 4Lo/4H.

Rear Diff Locker
: Not all 4WD models come with this. Switch/button activated. You must be in 4Lo or LL. It locks the rear axle so that it acts as one rod. If one wheel turns, so must the other so that not all power/torque is lost to the spinning wheel. Diff b/t Rear Locker and ATRAC is that with
Rear Diff Locker, both rear wheels spin in unison and steering tends to be rather difficult (so be careful near small ledges, ruts, drop offs). ATRAC, rear wheels are not locked and steering is not comprimised so you have more control of the vehicle. Apparently one works better than the other for certain situations while wheelin or you can do the Atrac-Locker Hack and have the best of Both worlds.

So at relatively high speeds TRAC will slow you down & aid in traction control in slippery situations, while VSC will give your more control during turns, skids, and saving your ass (roll over prevention).

While ATRAC and Rear Diff Locker is specifically for use in 4LO. While either of these are engaged, the TRAC and VSC is turned off. This makes sense, b/c they are safety systems to slow you down when you're going to fast, while ATRAC and RDL will aid to move you forward when you're going too slow or stuck.

Other Recommendations: Not necessary to be in 4H when it's raining or lightly snowing in the city, since this will deactivate VSC. VSC is what will save your ass at high speeds (per Thai). If you stay in 2H, you have TRAC and VSC to make necessary corrections if you slip & slide. If you do choose to put it in 4H for these situations, at least you still have TRAC working for you. But again, Thai says TRAC is turned off after 40+ mph or so. Many here feel you shouldn't be going fast (>40mph) while in 4H. 4H is probably more appropriate if you encounter thick/compacted snow or icey roads as FJJack mentions. You can quickly find out which is better with a test this winter. Try 2H and 4H and make up your own mind.

4H and 4L should generally be reserved for off roading use. 4H for light trails (gravel/dirt roads) and 4Lo for mod-large rutts/rocks. Obviously if a meteorite hits your town and all hell breaks loose then by all means put her in 4H/4Lo as needed.

Again, A great big thanks to KLD, Thai, CruiserLarry, RoverGGM, Alex, and countless others for their technical expertise on this forum.

Premium Member
441 Posts
VSC, A-TRAC, ABS & DIFF LOCK DRIVE MODES: Condensed overview

To read the original full thread and post questions/comments on this topic, please go to

I've tried to condense "everything" about drive modes (H2, H4, L4), VSC, TRAC, A-TRAC, and ABS, when they are active, and what limits there are to their use.

The version shown below is valid for 4x4 AT models where A-TRAC can be engaged while the rear differential is locked (*)

(*) Note: A-TRAC can not be engaged on some early model FJ Cruisers. This, however, can be addressed by implementing the A-TRAC hack as described on this forum.

It makes sense to me now, but I'll gladly try to improve it, make it easier to understand, etc. Think "when my kid brother borrows my FJ, will he remember how to use the drive modes?" :worried: Or would it be relevant to put a sticker up on the key things to remember?

Anywho, it's just a Powerpoint 2007 file, so if anybody is interested I'd be happy to provide it so you can change it to your heart's content.
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