You don't need to put chains on all 4 wheels. Just put em on the front

 

Given how many errors flash up on the MID over silly simple things like a barely low battery in back, I’m gonna go out on a limb here and suggest that the system would totally lose its mind and really shit the bed if it searched for and couldn’t find an entire 3rd motor expected in the rear.

 

You cannot simply turn "OFF" the rear even if there was a "fuse" somewhere. If you want to convert your AWD Sienna to FWD - you have to do 2 things. 1) Remove both axles to the MGR (so it does not drag your rear end like an anchor). 2) If there was that "fuse" or electrical disconnect -you need to do that too.

If you search for "RAV4 hybrid corrosion" or click here. You will realize if for some reason your rear MGR stops working - you will have to call for a tow truck.

 

Exactly this.... the AWD is part of a complete hybrid system...... not separated at all I would just erase this theory entirely

 

The purpose of 'converting' it to FWD is when CHP requires the use of tire chains, I only want to use one set and not have to carry and install a 2nd set.

That’s not required. The text of the law says traction control devices must be installed “on at least one drive axle”, not on all drive axles.

The Sienna is AWD but primarily FWD unless the front starts slipping. If you only want to carry and install 1 set of chains, do that, install chains on the front when required, and leave the AWD system alone.

VEHICLE CODE - VEH
DIVISION 12. EQUIPMENT OF VEHICLES [24000 - 28160]
( Division 12 enacted by Stats. 1959, Ch. 3. )

CHAPTER 5. Other Equipment [27000 - 28160]
( Chapter 5 enacted by Stats. 1959, Ch. 3. )


ARTICLE 4. Tires [27450 - 27503]
( Article 4 enacted by Stats. 1959, Ch. 3. ) 27459.

No person shall operate any motor vehicle, trailer or semitrailer upon any portion of a highway without tire traction devices when that portion of the highway is signed for the requirement of tire traction devices. In any case where a passenger vehicle or motortruck having an unladen weight of 6,000 pounds or less may be required by the Department of Transportation or local authorities to be equipped with tire traction devices, the devices shall be placed on at least two drive wheels, or the department or local authorities may provide, in the alternative, that the vehicle may be equipped with snow-tread tires on at least two drive wheels when the weather and surface conditions at the time are such that the stopping, tractive, and cornering abilities of the snow-tread tires are adequate. The snow-tread tires shall be of a type and design manufactured for use on snow as a replacement for tire chains or tire traction devices, shall be in good condition, and shall bear the marking of M-S, M/S, or other marking indicating that the tire was manufactured for use on snow, or, in the case of tires purchased before January 1, 1987, shall either bear the markings or, in the opinion of the inspecting officer, comply with the tread pattern requirements of Section 558.
(Amended by Stats. 1990, Ch. 71, Sec. 4. Effective May 1, 1990.)

California Code, VEH 27459.

Specifically, 4WD or AWD vehicles with snow tires, which are exempt from using chains in the low level chain requirements, are only required to carry a single set of chains, not chains for all 4 wheels:

VEHICLE CODE - VEH
DIVISION 12. EQUIPMENT OF VEHICLES [24000 - 28160]
( Division 12 enacted by Stats. 1959, Ch. 3. )

CHAPTER 5. Other Equipment [27000 - 28160]
( Chapter 5 enacted by Stats. 1959, Ch. 3. )


ARTICLE 4. Tires [27450 - 27503]
( Article 4 enacted by Stats. 1959, Ch. 3. )
27460.
Any passenger vehicle or motortruck having an unladen weight of 6,500 pounds or less and operated and equipped with four-wheel drive and with snow-tread tires on all four drive wheels may be operated upon any portion of a highway without tire tractiondevices, notwithstanding the fact that the highway is signed for the requirement of those devices and provided that tire traction devices for at least one set of drive wheels are carried in or upon the vehicle. The snow-tread tires shall meet the requirements specified in Section 27459, and the vehicle shall not, when so operated, tow another vehicle except as may be necessary to move a disabled vehicle from the roadway.
No person shall use those tires on four-wheel drive vehicles in place of tire traction devices whenever weather and roadway conditions at the time are such that the stopping, tractive, and cornering abilities of the tires are not adequate or whenever the Department of Transportation or local authorities, in their respective jurisdictions, place signs prohibiting their operation unless equipped with tire traction devices.
(Amended by Stats. 1990, Ch. 71, Sec. 7. Effective May 1, 1990.)

California Code, VEH 27460.

Chain Controls / Chain Installation | Caltrans

State of California

dot.ca.gov

 

I used to live in Denver, with frequent trips to Grand Junction, Colorado, over the Continental divide, and several passes. Chains are required there at times. But they are mostly enforced with Trucks. A truck which can not make it up the hill often blocks most or all of the entire road closing it. In many, many years of traveling this road, in a passenger vehicle, I have never used chains, nor have I been stopped..even when chains are "required". As posted, FWD is generally far superior in traction getting up a snowy hill than rear wheel drive. Since most cars now have front wheel/all wheel drive, this is primarily enforced in Colrado with trucks, which dont have front wheel drive.

Equally important, if not more important, is chains on the truck on the downhill side. Chains will prevent sliding in some conditions (not all). And, the last thing most people want is a very heavy truck sliding uncontrollably down the mountain.

In Colorado we have "runaway truck ramps"...always on the downhill side, strategically placed. Yes, I have seen trucks which went out of control use the runaway truck ramp.
This often happens with drivers who are unfamiliar with mountain driving. Trucks need to downshift and use the engine to slow the truck downhill, and not depend on brakes to stop the trucks massive weight. The brakes "heat up" on long downhill slopes by inexperienced drivers "riding the brakes". This can even happen to pickup trucks. I think there is a 7 percent grade for something like 7 miles coming off Vail pass. Riding the brakes for 7 miles is plenty of time for them to heat up and fail.

 

The rear motors do not live rent free. They help with regen braking.

 

To be perfectly honest - FWD regen braking is adequate and has no indication of "needing help" from the rear MGR. Do you have any articles/data proving that the rear "helps" and is an advantage over the FWD model Sienna ?

 

The purpose of 'converting' it to FWD is when CHP requires the use of tire chains, I only want to use one set and not have to carry and install a 2nd set.

I’m sorry, but if conditions are bad enough to require chains, I’m putting them on at BOTH ends of the vehicle, whether the axle is powered or not.

.

 

I’m sorry, but if conditions are bad enough to require chains, I’m putting them on at BOTH ends of the vehicle, whether the axle is powered or not.

Thats a good point, especially in downhill turns!
I thinking about carring a set of tire socks for the rear since they're light, compact and won't need to handle a lot of power and use my chains in the front.

 

There is only ONE hybrid battery, so that is either being charged (regen) or not whether you have fwd or awd.
I understand my AWD "only activates" when it senses a wheel slip, other wise its fwd. You cant have 4 wheel drive all the time (tho there are "full time" all wheel drive) because it damages gear (or tires) when you round a corner, because the inside wheel, turns less rotations than the outside wheel. I think Toyota solved that problem with the computer activating the awd only on a wheel slip detection. On our "old" 4wheel drives, we got out "put the hubs in" if we wanted 4 wheel drive, and, while on dry pavement the 4 wheel drive was disengaged. Later the "manual" transfer from 4 wheel drive to 2 wheel drive was automated. You used to have to put the hubs in in our 64 Jeep pickup.
I think the main difference in fuel economy between AWD and FWD versions has more to do with weight than anything else. Another axle is not under power, losing energy, because the awd is only active when needed.
The fuel economy difference between AWD and FWD is likely LESS than 1mpg difference. Fuel economy ratings are not in fractions, but rounded to whole numbers. So, if the AWD got 35.48 and the FWD got 35.52, then this minuscule difference would be reported as a full mpg less, because of rounding. Drivers have reported a half mile per gallon, or less, difference between AWD and FWD.
My advice is not to mess with the AWD/FWD but rather enjoy it when needed (no driver intervention necessary), and enjoy the extra money at trade in time or if you sell it, because the AWD is wildly popular. Its hard to get an AWD, because not as many are made and they are popular in areas where it snows, especially. Check the blue book and you will find AWD is worth more than FWD, and for good reason. The Sienna AWD is highly fuel efficient. If you dont need AWD, then you can probably trade in your AWD for a FWD, and probably get a good price out of your AWD. If you paid MSRP, you can likely sell it for more than you paid, if you kept it very nice and did not drive it over 12k per year.

 

I think the main difference in fuel economy between AWD and FWD versions has more to do with weight than anything else. Another axle is not under power, losing energy, because the awd is only active when needed.

Weight plus the fact that the rear axles are always turning when the vehicle is moving. As you stated, the motor is not always powered. It is only powered at startup from a stop until the vehicle gets to a certain speed (10-20 mph), up hills, around sharp corners, and when front wheel slip is detected. The rear always does regen when slowing down along with the front.

 

Im not an engineer, but understand the toyota rear axle is driven "only" by electric motors, which are only active when the computer detects slippage. So, if Im guessing right, the rear axle wont be "powered" unless there is slippage. That is, the rear axle "rotates" with motion, but its the same as a fwd as far as power loss goes, except when tires slip. But, I dont know. Just a guess.

 

You need to look at the Energy display on the audio screen. You will see that every time the car starts off, the rear wheels are powered as well as the other times that I mentioned. Now this powering of the rear does not cause a loss of mileage because power is being split between the front and rear whereas in the FWD the total power goes to the front. The FWD does not have axles that go from the hubs to the differential/motor assembly in the rear. The friction losses of the rear axles turning all the time is part of the reduction in mileage for the AWD. Note that the rear has one electric motor that powers both wheels.