SteveCraig

Sounds like the manual traction lock system is acting up. You should have seen torque applied to all 4 corners, up to about 20 kph. Believe a solenoid is energized by activating the console mounted lock button. Rarely used, it could have seized up.
My F150 uses a solenoid to engage the front differential. It failed over the Summer. Found out just after I buried it in a trench on a wet job-site.

User 41924

I've driven several RXs over the last few years, and the AWD system has never been an issue in the snow. Even my IS does pretty well. The truth is, accelerating is rarely an issue (assuming you stay on the road) under normal circumstances. Stopping or turning is more often the issue that causes difficulties, and tires are usually the culprit in those cases.

Keep good All Season or Winter tires on the car, and it will be a great car for you. No matter what the weather throws at you.

JDR76

According to Lexus (for 2014 at least) the only RX350 with VDIM is the F Sport.

http://pressroom.lexus.com/releases/...specs.download

But as you noted in another post, VDIM will only help you avoid an incident. I do not believe it would have helped you in your particular situation.

kitlz

Eric, I can't say how many times VDIM may have kicked in over the past four years. But I know one time it kept me from losing control on an icy road going downhill. I was trying to stop for a turn. Nothing wrong with this 'nanny' in my book. Turning off TRAC when stuck in snow is supposed to prevent the tires from spinning. I haven't tried it. But I keep it in mind in case it does.

ericsan13

My understanding is that the lock button only locks the center differential. 3RX lacks a LSD, except with the possibility of a logical implementation using brakes if you have VDIM. Therefore it is unlikely that torque would have been applied to 4 corners.

I think we are fooling ourselves when we think of the RX as an offroad capable vehicle. I would like to believe it as well, but my past experience in the snow proved me very wrong.

-Eric

afpj

According to the manual, after you engage the lock all-wheel-drive mode, it'll disengage as soon as you tap the brakes. To me it would be very difficult to rock your car out of a snowdrift because you always tap your brakes in between each try, or at least I do. Therefore you would have to hit that stupid button after each attempt to keep the lock all-wheel-drive mode engaged. As for the limited slip differential or lack thereof, the RX has traction control as the alternative.

vlad_a

Ah, AWD - my favorite topic.

The RX features what I would call a consumer-grade AWD. In the world of cameras, this would the the point-and-shoot type. It will take decent pictures to post on facebook, but not something you would print in a magazine.

What we have here is an FWD vehicle with a part-time AWD system that is controlled electronically. Unlike a mechanical unit, it does not have to wait for the wheels to slip before engaging. So, if you're starting from a standstill, it will lock center differential and will get the vehicle moving. It is also smart enough to tighten the center diff while turning aggressively to mask FWD tendencies of understeering (plowing through).
Should you take your RX350 off-roading, you will soon find yourself stuck. This would be the pro-grade and it is simply not built for it. Spend long enough spinning the wheels and the center diff will overheat and will completely disengage rear wheels, effectively turning AWD into FWD. 450h does not have a center diff, so it has that going for it, albeit the rear motor is less powerful than a direct mechanical connection in case of RX350.

Now, the good news is that most of the weight in the RX resides over primary driving wheels. With the high clearance it has and with proper tires (snow), it will be unstoppable in the snow.
However, once the speed increases, it simply reverts to FWD. That's a pretty big disappointment.

At the end of the day, I decided to get the best AWD vehicle out there - Subaru WRX STI.
With 4 differentials (double center), it is a beast. That's my choice for the fast line driving during snowstorms.
I can't wait to try it out. Should be here right before the snow season.

ericsan13

Hi Vlad,

Thanks for chiming in. The RX450h has one rear motor right? Therefore there is no LSD for the rear?

And two forward motors? Therefore the RX450h should have LSD on the front wheels at least?

-Eric

vlad_a

Hi Eric,

While there indeed is a single motor in the rear, the front 2 electric motors are not dedicated to each driving wheel. They actually control the gasoline engine, which is wedged-in between the two through a planetary gearset:
http://eahart.com/prius/psd/
Therefore the 450h does not have a transmission in a traditional sense. Although PSD qualifies as a CVT, it really isn't.

So, this leaves us with 2 open differentials, front and back. No center diff is necessary.

VDIM can act as a logical LSD, which it may to an extent. I would question its effectiveness, as the RX is a torque-steer pig when it comes to flooring it.

An old trick for RWD vehicles with open diff is to partially apply the parking brake to get the vehicle unstuck on slippery surfaces. I have done this to my IS300, as the Torsen LSD reverts to open diff if one wheel is spinning freely.

I am not sure if it is even possible to disable VDIM and VSC in the RX. There is a Trac OFF button that temporary disables traction control under 25MPH. If one is to hold this button while stopped, it will turn off the traction control completely until the next engine restart.
I found one caveat to this in a loaner IS250AWD - the cruise control stops working in this mode. I have not tried it in the RX. That was an unpleasant find because I spend 90% time driving my IS300 with traction control off and it has no VSC. Of course, it is a moot point for the RX - it has a much different purpose.

LeoDLion

We were in Texas when we purchased the RX350 without awd. Then we moved to a place that have snow sometime. Got to buy a AWD... Subaru Outback.

hovbuild

LOL My buddy just bought a Outback. He made fun of me for spending the extra for the Lexus. We swapped cars for a day, it took me 3 days to hunt him down and give him back his car..LOL Now the outback might just be a better off roader but even he admits that he might go in the woods once every 5 years.

nipponbird

Snow is something your grandmother might have seen where I stay (not that South Africa don't get snow, but I'm in the northern parts where the platinum is mined for your emission cats), so I cannot comment on the RX's abilities in snow. However, forget about an RX as an off-roader. It is at best a vehicle which can handle a poorly maintained paved road better than an ordinary sedan.

MRJJP

Sounds like a new set of tires is in order.
I always start out in 2nd gear in snow conditions........ The fist gear is often too much torque for snow conditions.

raylor4

When snow conditions get REALLY bad on I-80 over the Sierras in California, CalTrans insists on chains on all four wheels on four-wheel drive vehicles. Now I know why, thanks to this forum. Shifting drive wheels. Typically, four wheel drive with no chains and all-weather tires will get you over the pass at 30 MPH in snow. For two-wheel drive cars, chains are required on the two drive wheels only.

ericsan13

Thanks, but i think a second set of tire cables is probably more likely to help in those conditions.

I don't think we are able to start in second gear. The snow mode did do a good job of retarding the throttle however.