Electronic Traction Control is the gift that keeps on giving

ETC wasn’t originally intended to be a 4WDer’s friend.

Electronic Traction Control main1

DESPITE being the best thing to happen to 4x4s for a very long time, Electronic Traction Control (ETC) wasn’t originally intended to be the four-wheel driver’s friend.

ETC came out of the push to make vehicles safer and was a next-step technology from anti-lock (or so-called ABS) brakes. Once the ABS hardware, namely the individual wheel-speed sensors, was in place ETC merely required software to do the opposite thing to ABS – that being to brake a spinning wheel rather than release the brake on a locked wheel.

ETC is simple in principle and, apart from a means to apply an individual wheel brake (rather than applying all four wheel brakes at once), just needs a conventional ‘open’ differential to get the job done.

Differentials, as found in both cars and 4x4s, allow wheels on different sides of the same axle to turn at different speeds, which is required for the vehicle to round a corner smoothly, as the outside wheel has to rotate faster than the inside wheel to cover the longer distance of the wider arc it is following.

Unfortunately, an open differential also allows the power from the engine to follow the path of least resistance. If one of the wheels across an axle has absolutely no traction and starts to spin once the power is applied, the differential will send all of the engine power to that wheel, which keeps spinning leaving the vehicle going nowhere.

However, if you apply the brake on that spinning wheel, as ETC does, and forcibly slow down that wheel, the differential will automatically start to feed the power to the other wheel where there will be more traction, hopefully sufficient to get the car moving forward.

Electronic Traction Control first appeared on a 4x4 in Australia in 1993 courtesy of the Range Rover, in what turned out to be part of the last upgrade to the first-generation Rangie. ETC was extremely effective on that particular RR as there was an excellent off-road chassis – thanks to the generous wheel travel afforded by its old-school front and rear live axles – for the ETC to profit.

Electronic Traction Control

At the other end of chassis design, namely fully independent suspension, ETC was also a game changer. Nowhere is this better demonstrated than with the Mitsubishi Pajero, which from 2000 on – courtesy of the NM model – adopted monocoque construction and fully independent suspension in place of the separate-chassis, rear live-axle design used on all previous Pajeros. In doing so the Pajero instantly became very ordinary in difficult off-road going. However, two years later the Pajero gained ETC and was transformed. It was still prone to lifting wheels, sometimes alarmingly so, but it would now get up gnarly hills rather than failing at the first difficult pinch.

There’s only so much ETC can do, though. It just depends on the chassis it’s working with and what it’s actually asked to do. Notably, when asked to control both inter-axle wheelspin and cross-axle wheelspin things get difficult.

This was the case when ETC was fitted to the Land Rover Discovery II in 1998, despite that generation Discovery having front and rear live axles. When the ETC was fitted, Land Rover did away with the lever-operated mechanical centre-diff lock. The lock was still in place inside the diff case, but the case top and shifter had been changed so the lock couldn’t be engaged.

Land Rover thought ETC could do both cross-axle and inter-axle control successfully, but had to reinstate the old arrangement where the driver could manually lock the centre diff, following poor press reviews and complaints from owners.

The problem of ETC trying to cover both inter-axle and cross-axle duties was well demonstrated in the ranks of soft-roaders, such as the Ford Territory AWD and shorted-lived Holden Adventra AWD. Both had three open diffs with ETC but struggled off-road beyond the limitations of their ground clearance and/or approach and departure-angle shortcomings. But, tellingly, another soft-roader of the time, the first-generation (E53) BMW X5, was transformed off-road when BMW replaced the open centre diff used initially with an electronically controlled self-locking centre diff, leaving ETC just to look after cross-axle duties.

ETC has, of course, come a long way since the 1990s, even allowing the driver to select specific operating protocols for various off-road situations; Land Rover’s Terrain Response being the original and best example.

More recently – and more simply – the new Toyota Hilux has one set of traction-control protocols for on-road driving and another set for off-road driving that come into play as soon as you engage 4WD. This off-road specific ETC, which Toyota calls ‘Active’ traction control or A-TRC, is so good it makes the rear diff lock on the mid- and up-spec models effectively redundant. In fact, you’re generally better off not using the Hilux’s rear locker, as engaging it also cancels the ETC on both axles.


WHILE Electronic Traction Control is the 4WDer’s friend, the associated technology known as Electronic Stability Control (ESC) is a hindrance off-road despite being a potential lifesaver on-road.

ESC helps prevent skidding on slippery roads by selectively applying one or more of the individual wheel brakes, or by cutting engine power, or both. The trouble is this also slows the vehicle down, and this isn’t what you want when driving off-road in soft sand or deep mud where momentum is your best friend.

ESC is triggered when it detects the vehicle isn’t heading in the direction it’s being steered, which is often the case in soft, loose sand or in deep mud, as the driver attempts to correct the vehicle yawing from side to side. In a worse-case situation the ESC can become confused and just say “let’s shut everything down” and will attempt to bring the vehicle to a complete halt.

Thankfully, for sand and mud driving, most 4x4s have an ‘ESC Off’ switch that, at the very least, will desensitise the ESC, if not disable it all together. Selecting low-range also automatically disables ESC on most 4x4s.


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Fraser Stronach

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