Prospective Buyer - Traction Control Question

[BobBass]

This is a ridiculous question at this time of the year, but...

I am considering the 400h - probably wait for the '08 in hopes that the very last year of this generation will be tweaked to 'perfection' - but am concerned about what I read about its performance in snow. Although I hail from SE PA which isn't exactly in the snow belt, I live on a hill with an inclined driveway. Over the years, this has caused occasional problems with RWD and even FWD vehicles during significant snowfalls.

It just seems that an "AWD" vehicle with decent M&S tires should be able to handle "normal" snowfall conditions. Having to deal with a set of winter wheels/tires should NOT be necessary. From what I've gleaned, the problem seems to lie in the overeager traction control system.

There is a way to turn it off by pulling a fuse or something, but I wonder if the other "less invasive" way works on a 400h.

Most Toyotas can be put forced into "service mode" which will turn off TC and VSC. I asked the local Lexus dealer and they told me you couldn't do it with the 400h.

Would anybody out there be kind enough to try this and see if works on the 400h? It's one of these deals that once it's in "service mode" and TC/VSC is off, to take out of "service mode" it's a simple matter of turning the engine off. Next time you fire it up, it defaults to TC/VSC on.

Here is the procedure that was published in a major car enthusiast magazine:

1) Check that the Ignition is off and the shift lever position is at P.

2) Start the engine after turning the Ignition to the ON position.

3) Perform the following steps 4 to 8 within 30 seconds after engine start:

4) Turn the parking brake switch on.

5) Depress and release the brake pedal twice.

6) Turn the parking brake switch on and off twice while depressing the brake pedal.

7) Depress and release the brake pedal twice while the parking brake switch is on.

Notice: Steps 6 and 7 should be performed within 15 seconds each.

8) Check that the VSC warning light and slip indicator are turned on.

If they are not turned on, start over from step 1.

9) The brake control system will return to the normal mode by turning the Ignition to the ON position from off

Here's another wording from another source:

1. Make sure the car is in Park and the parking brake is disengaged before you start the car.

2. Start the engine.

3. Engage the parking brake.

4. Fully depress the brake pedal and then release.

5. Fully depress the brake pedal and then release.

6. Disengage the parking brake.

7. Fully depress and hold down the brake pedal.

8. Engage the parking brake, then disengage it (while holding down the brake pedal).

9. Engage the parking brake, then disengage it (while holding down the brake pedal).

10. Release the brake pedal.

11. Engage the parking brake.

12. Fully depress the brake pedal and then release.

13. Fully depress the brake pedal and then release.

For me, this would be a "last resort" if I were to get stuck halfway up my hill or driveway. I would never do this on a whim and deliberately go out in a major snowfall just to test the limits of the 400h.

Thanks to anyone who wants to give this a shot.

Bob

[skyfish400h]

Thanks to anyone who wants to give this a shot.

Bob

The second set of instructions is vastly more clear... I've printed it out and will try it out tonite.

[wwest]

Thanks to anyone who wants to give this a shot.

Bob

The second set of instructions is vastly more clear... I've printed it out and will try it out tonite.

If I owned an RX400h I would very likely modify the TC electronics(***) so that EVERY time the accelerator pedal is depressed, or farther depressed, TC would "sense" an ever so slight wheelspin/slip on both front wheels and thereby immediately bring the rear drive on line.

But I suspect that the RXh may do that anyway in an actual case of need, front wheelspin/slip, say on an icy surface.

For a true FWD or front torque biased AWD it is an important matter concerning the safety of the passengers that TC react immediately and instantaneously to front wheelspin/slip by dethrottling the engine and using braking to most quickly moderate the level of torque being applied to the (SLIPPERY) roadbed via the road/tire interface. To do otehrwise would dramatically increase the probability, DANGER, of loss of directional control due to engine torque, TOO MUCH OF.

On the other hand were you to be able to IMMEDIATELY and INSTANTLY transfer ALL or the majority of the the engine driving torque to the rear wheels the very instant front wheelslip/spin is detected that would allow you to maintain directional control using the front traction coefficient while still driving the vehicle forward. Sorta like the SH-AWD system.

The RXh quite clearly could have the ability to implement such a technique.

But does it...?

*** "Pre-process" the front ABS wheelspeed sensors' signal so that they indicate a "falsely-rising" wheelspeed, a wheelspeed slightly above present roadspeed, just for a few hundred milliseconds each time increased drive torque is demanded via the gas pedal.

Again..

Unlike the "standard" AWD RX, If the AWD RXh's TC firmware is well engineered, designed, there would be no need to disable TC in the "ordinary" circumstances some of us encounter during the winter months. But I believe I have read somewhere recently that the 2008 RX350 has a TC and a VSC disable function. Apparently TC must be disabled first and only then can you proceed to disabling VSC.

[SOMEONE ELSE'S GOT MY NAME]

No one w/ decent snow tires has ever needed to disconect their T/C. That being said, it will be disabled if the speed sensors are disconected ... but you didn't hear it from me.