Weird Traction Control On Dry Street

The traction control system on the Prius is less than perfect. There are modern traction control systems out there that do not react the way the Prius' system does. Hopefully this will be rectified in the 2010 model. My 2004 Land Rover Discovery had this nasty traction control behavior as well. What happens is the traction control can kick in during a most inopportune time... such as slowing down on a turn, coming to a stop sign, etc. All it takes is a jarring of the wheels over bumps in the road while braking. For example, hitting the brakes while crossing the reflectors separating a turn lane... or hitting a pothole right before a stop or turn. What makes this dangerous is it kicks in the ABS and increases your stopping distance. It is possible to "ABS your way" into having your nose sticking out into an intersection if you're not careful. It is also disconcerting and can lead to errors in judgement from the shock of losing braking power.

Unfortunately, this is the normal operation of the Prius traction control system. You do not need to see your dealer. Just be aware of situations where it might kick in and try to plan for them. For instance if I'm coming up to a toll booth and need to cross the reflectors to change lanes at the last minute, I will let off the brake until I cross over them.

One thing that makes this worse on the Prius is the bicycle tires that come on the non-touring models. Since I upgraded to Goodyear Comfortreds, I have not had this happen to me again. Also note that increased tire pressure (as is recommended here) to 42/40 on the stock GY tires will make them stiffer and increase the sensitivity of the traction control to kick in at inopportune times.

As a side note, when Land Rover changed from the Discovery to the LR3, the entire traction control system was new, and our LR3 (now gone, thank goodness at 14mpg) never ever displayed this issue.

 

Same answer here. I tend to have this happen when headed downhill and the rear tires hit a bump (e.g., manhole cover) while braking. For the first few months that was scary, now I've learned to drive expecting that to happen. I almost never set it off any more.

The nearest I came to an accident was pulling off the road, onto a gravel shoulder. Same deal - no brakes for a fraction of a second. You just have to be cautious in situations like that.

 

One thing to remember about losing traction when braking is to keep braking. Only the regenerative braking is cut, and the friction braking takes over and works as it would with a normal car. Sometimes the transition causes Prius drivers to ease up on the brake, thereby making the problem worse. Keep pressing the brake pedal and the loss of traction will be nothing more than a weird sensation, not a safety issue.

I'll second the comment about the OEM tires. They aren't very good.

Tom

 

This doesn't seem like a traction control issue. Based on my (admittedly limited) understanding, TC applies only when one or both drive wheels lose traction under acceleration.

Instead, this seems like this brake idiosyncrasy described by Hobbit (excerpted from this):

One really annoying circumustance is when a bump of just the right size or
time-constant is hit while regen braking -- the torque blip causes the ECU
to get confused and give up on regen for quite some time, transitioning
to physical brakes for no real good reason. The pressure indicator makes
this obvious. No means of recovery other than waiting long enough has
been found yet [and it's difficult to experiment if what you really need
to do is STOP]. The best bet seems to be shifting quickly into "B" and
letting the engine spin to bleed off some of the energy; regen charge
current into the battery is also generally higher in "B" and you can recover
a little more energy than by simply continuing on physical brakes alone.​

 

The results are the same, even if the triggering event is different. In either case the Prius will switch to friction brakes, and the fastest way to stop is to continue pressing the brake pedal. Shifting to B won't stop you any faster, although it will allow the recovery of a little energy. If you really need to stop, playing with the shifter is a bad idea. Just cram on the brake pedal and be done with it.

Tom

 

It should be the traction control light that flashes. That's the one you will see when regenerative braking is lost due to bumps or traction issues.

Tom

 

The real answer here is that the Prius "traction control system" is mis-labeled. It's really a transmission over-rev protection system. When one of the wheels loses traction and is in danger of spinning, the system stops all traction to protect the engine, transmission components from hitting high rev numbers (some components could go over 10,000 RPM).

I usually encounter the problem when making a right turn from a stop when there is some sand on the road (a fairly common occurrence on Long Island). In addition to being very annoying, it's a safety hazard, especially when there is a car directly behind you.

My Toyota dealer checked the system and said that it was operating correctly.

 

Great, thanks for the clarification. The only time I've seen the TC light come on is under acceleration on wet pavement, gravel surface, etc.

 

I think the issue is simpler than is being suggested. I think Toyota uses older or cheaper/inferior parts, sensors, control units, or all of the above. Either way, the behavior of the TC/ABS system in these circumstances is not good and borders on dangerous. Keeping or even increasing pressure on the brakes does not help. The modulation of the ABS once the TC kicks in increases stopping distance regardless of user input. Of course, releasing pressure on the brakes in these types of situations will make it worse.

 

I think a lot of Prius owners have noticed the somewhat delayed change from regen to friction brakes when the system transistions. If while braking a front wheel happens to hit a pothole, a manhole cover, some gravel on top of pavement, or anything else that can upset traction, you will experience the upset

One thing to keep in mind about ABS, is that it generally does *not* improve stopping distance. Some claim that ABS will keep the tires right at the edge of lockup, to maximise braking, that seems dubious.

ABS is primarily intended to keep you in control under hard/panic braking. In an emergency, you stomp the brake pedal on a non-ABS vehicle, you lock up all the wheels. Once that happens, steering is imposible, you will also possibly enter a sideways slide

ABS can be designed to be very "smart" or it can be pretty simple and downright dumb. The ABS on early to mid 1990 GM pickups was downright scary, even a hint of a wheel locking up and the ABS became oversensitive. Back in Utah, I knew of such pickup owners pulling the ABS fuse to have "normal" brakes

Both my Prius and my FJ have ABS, EBD, Brake Assist, electric power brakes, and traction control that cannot be defeated. Toyota has clearly learned from the Prius.

The ABS in my FJ is far superior. A few times I've had to avoid deer on the drive out to my hobby farm. Since there is no delay from regen to friction, the brake assist immediately pushes massive braking. As the FJ has a four wheel, four channel system, the results are superior to the Prius

With the traction control, the FJ never kills all the power. I've purposely driven my FJ into a snow drift at low speed, in 2wd, until it bogged down. Not only is it very easy to "rock" the FJ, once you floor the gas pedal and keep it floored, the Trac appears to switch to a desensitised mode.

I find it a bit odd that Toyota hasn't applied these lessons to the current model Prius. The 2008 I test drove was far better behaved than my 2004, especially on snow and ice. However, there is room for improvement. Perhaps they are saving major improvements for the new model