Have you ever wondered what that mysterious fourth knob of the HVAC system does on your Tacoma? Not many people know this, but that is actually the four wheel drive selector switch!
Ok, all jokes aside, I’ve always thought it was a terrible design decision to put a knob of the same shape and size right next to the climate control dials. Now I imagine almost all of you knew what the control was for, but today we’re going to get into the details of what happens when you twist that dial (or move the lever if you’re still rocking a first generation truck!).
Tacomas use a part-time four wheel drive system. Part-time four wheel drive is NOT all wheel drive! They work in very different ways and while Subaru may show drivers confidently driving in the rain because they have all wheel drive, you cannot and should not expect similar behavior or performance from your truck.
Each system has its advantages and shortcomings but it is important to know the differences so you do not damage your truck.
4WD mode selector – How to use it:
As mentioned above, the second and third generation trucks have a knob just to the right of the steering column with three positions: two wheel drive (2WD on third gen, H2 on second gen), four high (4H), and four low (4L). First generation trucks use a floor mounted lever to the right of the gear shifter. This has the same 3 modes, but also includes a neutral (N) position as well.
Two wheel drive is the easiest to understand. In this mode, the engine is only providing power to the rear wheels of the truck. This is the default mode that will be used for all of your normal driving on pavement.
The Tacoma four wheel drive system allows you to switch to 4H at speeds up to 60 miles per hour. This means that you can be in drive (or any forward gear with a manual), neutral, or reverse and twist the knob to the 4H position. Doing so will then send power equally to the front and rear wheels. This should only be used off road or on snow/ice covered pavement.
|Available Settings||Label||When To Use|
|2 Wheel Drive High||2WD or H2||Regular driving on dry ground|
|4 Wheel Drive High||4H or H4||Driving at higher speeds on slippery ground|
|4 Wheel Drive Low||4L or L4||Slow speed crawling where extra torque and control are required|
When turning, the wheels will all be covering a different distance. If four wheel drive is engaged, the system will be forcing them to turn at the same speed which requires tire slippage. This slippage cannot occur as easily on dry pavement, which in turn puts additional stress on the mechanical components of your truck.
Now the system won’t immediately fail if you drive a short distance on pavement by accident, but it does put a tremendous load on the system and should be avoided. The sharper the turn, the more stress will be induced on the truck. You can switch from 4H back to 2WD at any speed.
The 4L mode only comes into play when things are getting serious! 4L gives you the same four wheel drive traction advantage of 4H, but greatly reduces the gearing. This can be used if you’re attempting to climb a very steep grade or descending, as the lower gearing will provide additional engine braking which can make a slow, controlled descent much easier for the driver.
The lower gearing can also be advantageous if you’re pulling a stuck vehicle out of the ditch, yanking out a tree stump, or other scenarios that benefit from the extra torque where higher speed is not needed.
To select 4L, bring your truck to a COMPLETE STOP, shift to neutral, then rotate the knob to the 4L position. The knob requires you to push it in a bit as it goes from 4H to 4L. You should also come to a stop when going from 4L back to 4H.
First generation trucks had two different style shifters for four wheel drive. Some trucks used what was referred to as a J-style shifter which has the 2H, 4H, Neutral, and 4L positions. Others had a shifter with an L4, N, and H position and used a button on the side to engage 4H.
The trucks will display a light on the dash when the four wheel drive system is active. Although it is safe to switch to 4H mode while in motion, do not do this if the wheels are actively spinning- the sudden change in speed applied to the front which is presumably turning slower than the slipping rears could damage the system.
Tacoma transfer case designs
This is where the magic happens, my friends! The transfer case is the unit that controls whether power is sent to the front wheels. It also has the additional gearing that comes into use when 4L is selected.
First generation trucks used electronically controlled actuators on some models and a physical shifter on others. The subsequent generation switched to electronic actuators across the range using two different motors to engage the four high and four low modes. Third generation simplified this design with an actuator that required only a single motor.
While second generation was operated exclusively via electronics, it did not have the brains to provide helpful diagnostic codes when things went awry. This was a big improvement on the third gen models as it can point you in the right direction when troubleshooting the system.
Front differentials in Tacomas
This is obviously another very important piece of the system. The front differential on all Tacomas is an “open” unit which means that the wheel with less resistance will be the one that receives power. While not ideal for hardcore off-road situations, this is what you will find on just about all trucks and SUVs from the factory.
Some of the earlier first generation trucks had the old-school manually locking hubs. This means in order to engage your four wheel drive system, you had to park the truck and go to both front wheels to turn the dial which engaged the axle on either side.
While some enthusiasts prefer this system for its simplicity, there is something to be said for the convenience of not getting out in the snow and mud. Also, sometimes coming to a stop is the best way to get stuck in a hairy situation. If you’re using manual locking hubs, you better plan ahead.
Toyota realized the benefits of “shift on the fly 4wd” systems and came up with the Automatic Differential Disconnect (ADD). This added another actuator on the front end which moves a coupling to engage or disengage the passenger side axle, all from the comfort of the cab. ADD uses an actuator on the front end by sliding a sleeve axially, coupling the axle to the differential.
To summarize, the transfer case is what controls whether or not the front prop shaft (driveshaft between transfer case and front differential) is turning but the axles won’t be engaged unless the hubs are locked or ADD is engaged.
Tacoma rear differential – LSD, E-Locker, etc.
While these are not unique to the four wheel drive Tacomas, I thought it was worth touching on this area as the differences here do affect the off-road performance of your truck.
Most of the second and third generation trucks have an automatic limited slip differential (Auto-LSD). This is a confusing name for the system as most people are familiar with traditional LSDs which have been around for many decades and use a purely mechanical system to send power to both wheels.
The Auto-LSD system, however, is actually a brake-based, electronically controlled way to do this. It uses the computers and ABS system to apply braking to the wheel that is slipping and transfer power to the opposite wheel. Mechanically, the guts inside are simply an open differential. The Auto-LSD is activated via a push button and like other systems, should only be used on loose surfaces.
The first few years of the second gen (2005-2008) used a traditional mechanical limited slip differential. I imagine the change was done as a cost savings since this functionality is obtained with some extra programming and the existing ABS module and wheel speed sensors.
Third generation trucks have an electronically controlled locking rear differential on the TRD Off-Road and TRD Pro trim levels. This a true locking diff so the left tire is turning the same speed as the right. Like using the 4H and 4L settings, you will not want to lock the differential unless you are on a loose surface that allows tire slippage.
Usage on pavement will put extra stress on the system and potentially break axles or parts in the differential. Toyota recommends reducing your speed to less than 2mph (aka you should probably just come to a complete stop) before locking the differential. They also caution that it should only be used at low speeds (less than 5mph) and that it should be turned off when not needed.
I believe the first gen only offered an LSD as a dealer installed TRD option. Chances are most first gen Tacomas you come across will have an open diff or aftermarket parts installed. It seems that the TRD accessory is incredibly rare.
Other electronic 4WD systems in the Tacoma
The third gen truck offers a variety of different systems to help you navigate tricky situations. Some of these work with the four wheel drive system and others are basic safety systems.
Traction control (TRAC) is just your basic traction control that will prevent you from doing smoky burnouts. This simply cuts throttle if it sees a sudden jump in wheel acceleration. Turning this off can be beneficial on loose surfaces, but don’t get crazy hammering on the gas pedal- that’s how you break things.
VSC is stability control and will keep you from going full Mustang into a curb. Turn this off if you’re planning to practice your drifting skills in a snowy parking lot.
ATRAC works similarly to the Auto-LSD in that it uses the brakes to control wheel speed, but this system is monitoring the speeds at all four wheels and is attempting to mimic the function of locked front and rear differentials. It’s rather impressive and can get the Tacoma through some rough terrain. This system can only be activated when the truck is in 4L.
Crawl Control works as your off-road cruise control by using the brakes and throttle to maintain a very slow, but consistent speed.
MTS (Multi Terrain Select) offers several different modes that Toyota has optimized for various scenarios. This functions similarly to ATRAC, but with different parameters for how much wheel slip it allows.
Just a reminder – Use it or lose it!
Toyota recommends that you engage the four wheel drive system for about 10 miles per month. This will keep the components lubricated and operating freely. It’ll save you headaches down the road if you keep the system exercised on a regular basis. If you don’t have the ability to get off the pavement to do this, just make sure you’re driving in a straight line.
Even if you can’t do the whole 10 miles, turning all of the parts over and letting the actuators do their thing just a bit is better than not at all. You don’t want to not touch the selector for months or years and then find out it doesn’t work when you really need it most!