Bushtracker Bandicoot
21-07-2008, 08:21 PM
Here's one disconcerting experience regarding the Jeep and its traction control system. I’ve been driving 4WDs since 1976 when I got an open off-road licence for 4WDs and the largest rigid body off-road trucks the Army had at that time, while I was in the Army Reserve. However, those days off-road vehicles and trucks were mechanically simple (if frequently unreliable) with carburettors and crash gearboxes. Almost no instruments and no computers. They didn't even have power steering.
My first 4WD excursion with the Jeep was to Fraser Island. I promptly got bogged in some relatively deep sand, but nothing that would have worried me previously in Land Cruisers or Patrols, and this is despite the Jeep’s constant 4WD and fully locking electronic diffs front, rear and centre. The Jeep got into the sand and the engine just seemed to die. Afterwards I went and read the owner’s manual (yes, it’s a boy thing). It clearly states that the Electronic Stability Program (which includes the traction control system (TCS)) has three settings: fully on, partially off, and fully off, and that in deep snow, sand, gravel or mud the Electronic Stability Program should be turned to at least the partially off setting. I had to read the book several times to figure out why (badly explained). However, with the ESP fully operational, the Jeep’s wheel sensors detect wheel slip within 1/8th of a wheel revolution. The computer responds by applying the brake to that wheel, and with its three electronic diffs, applies more power to the wheel /s that still have traction. It also reduces engine power (if necessary) to eliminate wheel spin. This sounds fine and dandy. Who can argue with putting more engine power to the wheel/s that have traction?
However, in deep snow, sand, mud etc, some wheel spin is essential to get going—or to stay moving. This was the problem on Fraser Island—the ESP wasn’t at least partially disengaged. One wheel started to spin; engine power was transferred to other wheels...they also start to spin...engine power is reduced and, hey presto, there’s no more wheel spin but also no engine power and no forward motion!
Apart from embarrassment, this didn’t cause any real problems on Fraser Island. This wasn't the fault of the vehice, it was fully operator error!
However, when going into Blencoe falls recently from the West (the Herbert River side) and towing our new BT, the failure to put the ESP into at least partially off mode, created a potentially dangerous situation.
I was pulling the van up a steep, fairly slippery (it had started raining) and windy hill. It was going fine and felt sure-footed and safe, and would have continued to go fine and safe unless the engine management system intervened—which it decided to do. About half-way up the hill, in the space of 2 to 3 seconds, I heard one wheel start to spin (only for the smallest fraction of a second, then it stopped spinning) and then the engine just closed down over the next couple of seconds, even though I put the foot flat to the floor. As soon as the power loss started to happen, I realised what was going on, but with so many wretched buttons on the dash, by the time I found the ESP button, I was stationary holding the vehicle on the service brake.
So here I was on a steep greasy hill dragging a 3.5 tonne 'condominium on wheels' with no forward momentum. There was no practical chance of reversing down the hill around the various bends on this surface.
I turned the ESP to partial off, and fortunately, with some wheel spin and a small amount of fish-trailing (and a few quick prayers), the Jeep and van started climbing back up the hill. Needless to say, I left the ESP in the partial off mode until we got completely out of any chance of wheel spin.
It now seems to me that the TCS is designed for high speed driving where one wheel temporarily loses traction due to (say) some loose gravel or perhaps water or oil, or when off-road and climbing over rocks where one wheel might be lifted into the air on each axle but the other wheels are solid on the ground...it should be turned off for slippery conditions where some wheel spin is essential.
In case you’re wondering what the “fully off” mode is for ESP. As I understand it, this also turns off the Electronic Roll Mitigation functions and also the Stability Control functions that automatically correct oversteer and understeer. The Jeep automatically turns all these functions off when in low range 4WD, but they can also be turned off manually in high range 4WD.
So make sure you turn the ESP to at least partially off if heading onto tracks where some wheel spin is important (along with NOT losing your engie power!)
My first 4WD excursion with the Jeep was to Fraser Island. I promptly got bogged in some relatively deep sand, but nothing that would have worried me previously in Land Cruisers or Patrols, and this is despite the Jeep’s constant 4WD and fully locking electronic diffs front, rear and centre. The Jeep got into the sand and the engine just seemed to die. Afterwards I went and read the owner’s manual (yes, it’s a boy thing). It clearly states that the Electronic Stability Program (which includes the traction control system (TCS)) has three settings: fully on, partially off, and fully off, and that in deep snow, sand, gravel or mud the Electronic Stability Program should be turned to at least the partially off setting. I had to read the book several times to figure out why (badly explained). However, with the ESP fully operational, the Jeep’s wheel sensors detect wheel slip within 1/8th of a wheel revolution. The computer responds by applying the brake to that wheel, and with its three electronic diffs, applies more power to the wheel /s that still have traction. It also reduces engine power (if necessary) to eliminate wheel spin. This sounds fine and dandy. Who can argue with putting more engine power to the wheel/s that have traction?
However, in deep snow, sand, mud etc, some wheel spin is essential to get going—or to stay moving. This was the problem on Fraser Island—the ESP wasn’t at least partially disengaged. One wheel started to spin; engine power was transferred to other wheels...they also start to spin...engine power is reduced and, hey presto, there’s no more wheel spin but also no engine power and no forward motion!
Apart from embarrassment, this didn’t cause any real problems on Fraser Island. This wasn't the fault of the vehice, it was fully operator error!
However, when going into Blencoe falls recently from the West (the Herbert River side) and towing our new BT, the failure to put the ESP into at least partially off mode, created a potentially dangerous situation.
I was pulling the van up a steep, fairly slippery (it had started raining) and windy hill. It was going fine and felt sure-footed and safe, and would have continued to go fine and safe unless the engine management system intervened—which it decided to do. About half-way up the hill, in the space of 2 to 3 seconds, I heard one wheel start to spin (only for the smallest fraction of a second, then it stopped spinning) and then the engine just closed down over the next couple of seconds, even though I put the foot flat to the floor. As soon as the power loss started to happen, I realised what was going on, but with so many wretched buttons on the dash, by the time I found the ESP button, I was stationary holding the vehicle on the service brake.
So here I was on a steep greasy hill dragging a 3.5 tonne 'condominium on wheels' with no forward momentum. There was no practical chance of reversing down the hill around the various bends on this surface.
I turned the ESP to partial off, and fortunately, with some wheel spin and a small amount of fish-trailing (and a few quick prayers), the Jeep and van started climbing back up the hill. Needless to say, I left the ESP in the partial off mode until we got completely out of any chance of wheel spin.
It now seems to me that the TCS is designed for high speed driving where one wheel temporarily loses traction due to (say) some loose gravel or perhaps water or oil, or when off-road and climbing over rocks where one wheel might be lifted into the air on each axle but the other wheels are solid on the ground...it should be turned off for slippery conditions where some wheel spin is essential.
In case you’re wondering what the “fully off” mode is for ESP. As I understand it, this also turns off the Electronic Roll Mitigation functions and also the Stability Control functions that automatically correct oversteer and understeer. The Jeep automatically turns all these functions off when in low range 4WD, but they can also be turned off manually in high range 4WD.
So make sure you turn the ESP to at least partially off if heading onto tracks where some wheel spin is important (along with NOT losing your engie power!)