Over the last couple of days our 2004 Toyota Prius has sent out numerous Electronic Skid Control false alarms. Light flash, brakes sometimes grab to "correct" a non-existent slide and, most of all, a piercing piezo beep fills the cabin.
The first time it happened I has sweeping through an on-ramp. Was I going that fast? Not really. Did I hit a bump, or something? Probably. I didn't think much of it.
Next morning, my wife grabbed the keys to take the kids to school, 10 miles distant. She called back in 5 minutes.
"Get the van ready," she said. "I'm bringing this thing back. The skid control is going nuts."
One of the places she said it happened was the road above, not 200 yards from our home. There is nothing in the way of G forces here, just a gentle bend to the right as you coast slightly downhill to the stop sign ahead. It happens every time, exactly where this picture was taken, so long as the speed is 33 mph or higher. The posted limit is 35 mph.
And then I remembered some things that might add up to a theory...
When I first drove the Prius home from the office, I noticed was off to one side--way off. Ten degrees, at least. Could be alignment, could be excess "conicity" in the well-worn tires, could be lots of things.
Here's another piece of information: the ESC false alarms only occur when turning right. I proved that to myself with some lane change maneuvers on a deserted road. There are no problems turning left.
Here's how these two facts add up to an early ESC warning. Let's say my local bend in the road requires 70 degrees of steering input. The ESC computer actually measures this using a steering angle sensor deep in the steering column. It compares the measured steering angle to the cornering G measured in another sensor to calculate the degree of understeer or oversteer.
But if the wheel is at minus 10 when I'm going strainght, my 70-degree right input will measure only 60 degrees on the steering angle sensor. The computer could be comparing this to the lateral G being produced and say to itself "That's not enough steering input for this amount of lateral G. The car must be oversteering. I'd better DO something."
Beep! Beep! Beep! Beep! <brake grab> Beep! Beep! Beep!
Now, you're probably think about left turns of the same magnitude. The computer would see 80 degrees, and think this was more understeer than usual. Well, oversteer is the more heinous situation, (to an ESC computer, at least). It will be much more sensitive to oversteer.
Beyond that, I'd like to think such systems would be smart enough to "learn" where straight ahead is and compensate for worn tires or bad wheel alignment. Maybe some do and some don't. The technology was still in its infancy when this particular car was originally in development.
For grins, I looked underneath for any signs of damage. Was there a rock strike? Is something bent. Nope. Everything looks just fine under there.
Damage can't explain it. The steering wheel is off center for some other reason. Here's my plan:
First: I'm going to install new tires. One of them is bad anyway, but it's a rear, and rear tires don't cause pull or steering wheel misalignments. Besides, the front ones are worn, too, and worn oddly. There could be excess conicity at work, enough to create sufficient right-hand force to make me have to steer left to go straight.
If these were good tires, I'd simply swap the front tires left-to-right to redistribute the conicity so it acts in the opposite direction. If conicty was the culprit, I'd see a change at the steering wheel. But since these tires are worn, I'm going straight to new ones.
Second: If the steering wheel is still "off" to one side after the new tires, I'll adjust the toe-in at the tie rod ends to recenter the steering wheel.
Third: There is no third. If these two steps don't work, my theory is wrong and I'll have to take this Prius to the dealer.
But I think I'm right. We'll all soon see after I get back from the tire store.
Dan Edmunds, Director of Vehicle Testing @ 84,490 miles
subaru123 says:
05:16 PM, 09/25/10
Well just about anything will trip the Prius' traction control. For example, it's raining and you have to stop in a small puddle at a red light. Anything but coasting away will trip it. What there's some sand between where road A meets road B? Yep that will trip it to. Another time I sped up to change lanes. As i moved right (:o) the traction control tripped. Maybe your wife thinks she was in a race car lol.
kevm14 says:
05:48 PM, 09/25/10
I don't know if I'd say stability control was in its infancy in this car's development. I know it was optional in 98 on the C5 Corvette and standard by 2001. Then again, people think drive by wire throttle is "new"....97 Corvette had that. Though in the Prius's price class, stability control was pretty unheard of for the 2004 model year, so I'll give you that.
7driver says:
06:04 PM, 09/25/10
Hm, I thought ESC normally means a yaw sensor is on board and that it would have higher priority over a steering angle sensor input. Perhaps Toyota is behind the times or cost-cut it out. Either way, I'd have expected it to throw a diagnostic warning that it sensed something was off. Maybe Toyota cost-cut that out as well.
vt8919 says:
06:34 PM, 09/25/10
I hear the reason why Toyota has non-defeatable traction control is that it's supposed to protect the special hybrid components.
Technically, though, you CAN defeat it. Assuming it's not snowing in your area yet, I would suggest disabling it until it gets fixed. Unless the car is still under warranty... wouldn't want to void anything.
1) Turn the car to ignition by pressing START twice without pressing the brake.
2) Floor the gas pedal two times (two full top to bottom pressings)
3) Make sure the parking brake is on, and while pressing the brake pedal put the car into NEUTRAL
4) Again press the gas pedal two times
5) Push PARK and press the gas pedal two more times
6) Now put your foot on the BRAKE and press START one time while holding the brake down.
(according to http://wiki.answers.com/Q/Can_toyota_prius_traction_control_be_turn_off)
I've always wanted a Prius, but seeing as I'm in Vermont, I'm afraid that I would get stuck in the worst locations during winter.
pezzy669 says:
07:04 PM, 09/25/10
kevm14:
ESP was widely available on the '00+ VW Jetta/Golf/New Beetle. These cars also featured drive by wire since '00 so both features are not as hard to find as you may think. :)
creeper says:
07:07 PM, 09/25/10
VT- i think that's the self destruct sequence. maybe try with the joystick up up down down left right a b select start. that should work.
Dan: what happened with the mysterious mileage issue that everybody claimed was battery fatigue?
firstwagon says:
07:25 PM, 09/25/10
From what I've heard you have to disable it in the snow. It's so over protective that the car will just sit and go no where in deep snow. It doesn't allow any tire spining.
I'd just leave it off all the time. Serves no real propose if you know how to drive.
mustang5507 says:
03:25 AM, 09/26/10
off topic...but
one of your colleagues complained about a slight misalignment in the Sonata's dash panels. Check out the WAY uneven gap in that steering wheel center cap! That's at least 0.5mm.
sodaguy says:
03:29 AM, 09/26/10
Dan-
The Toyota VSC systems require a "zero point calibration" after an alignment. The issue you are experiencing sounds like the car is so far out of alignment that it is needlessly triggering the stability control system. A proper 4-wheel alignment and a "zero point calibration" should solve the problem, or should be the first step to solving the problem. I know the newest Hunter racks have an optional adapter that will plug into the vehicle's communication port to perform the reset, otherwise, the Toyota scan tool or a higher-level aftermarket scan tool will be needed.
sodaguy says:
03:33 AM, 09/26/10
Also, some forums state that it is possible to perform the zero point calibration without the scan tool, but the procedures will vary by model.
bodyblue says:
07:39 AM, 09/26/10
"Well just about anything will trip the Prius' traction control. For example, it's raining and you have to stop in a small puddle at a red light. Anything but coasting away will trip it"
Our Prius is not like that at all, it is a 2005. The only time I have noticed it in use is when I floored it in the rain just see what it would do...the light flashed when it started to slip and power was reduced.
"Perhaps Toyota is behind the times or cost-cut it out. Either way, I'd have expected it to throw a diagnostic warning that it sensed something was off. Maybe Toyota cost-cut that out as well."
Six years is an eternity in car electronics.....but no car will give you a warning if the alignment is off. There was no cost cutting as very few cars back then had ESC in its price class.
subaru123 says:
07:59 AM, 09/26/10
@bodyblue
Mine is a 2008. For me any thing more than half throttle in the rain trips it. It's sometimes a problem when merging on a highway from a side street.
chunky_azian says:
12:58 AM, 09/27/10
@7driver
"Hm, I thought ESC normally means a yaw sensor is on board and that it would have higher priority over a steering angle sensor input. "
Steering wheel sensor measures the ordered turn rate. Yaw sensors measures the actual turn rate. Yaw sensor data doesn't tell whether the car is understeering or oversteering if it isn't cross checked with the steering wheel sensor. Both sets of data have to agree or ESC goes nucking-futs.
vvk says:
07:13 AM, 09/27/10
Just FYI, first generation Toyota Crown Majesta (S140) sold between 1991 and 1995 was the first Toyota to offer Vehicle Stability Control.
mieden says:
08:01 AM, 09/27/10
vvk, that wasn't a fully electronic, 4-channel yaw control system. Mercedes was first to market with stability control in its $140,000 1996 (or 97 depending on market) W140 S600. They were first to market but since they shared development with Bosch, Bosch was able to license the technology (in another name) to BMW the following year. The "Electronic Stability Program", ESP for short, was optional on every Mercedes model by 99 and standard on every Mercedes by 2002. Also, Bosch was first to market with twin "Electronic Throttle Actuators" (drive-by-wire) in BMWs 1988 750iL. Legacy ETA's for early German cars can still cost over $1000 to replace!
roadburner says:
08:13 AM, 09/27/10
Another FYI; the BMW M70 V12 had dual drive-by-wire throttles when it was introduced in 1987...
stovt001 says:
11:04 PM, 09/27/10
My Miata, even as a 2006 model, has no such electronic nannies. The closest thing it has is ABS. If my steering is off, it will have adverse effects on the handling, but it will not confuse any computer in the slightest bit and cause that computer to "correct" for me. If I was really oversteering, there is no computer to weigh lateral Gs against steering input and put a damper on the fun. Instead, I would receive that information directly from the road through the tires, through the steering column, through the steering wheel, and into my hands. I'd perhaps unwind a bit, maybe even a bit of opposite input depending on the severity, and the exquisite neutral balance of the vehicle would practically take care of the rest. And this would all be perfectly intuitive. It needs no electronic nannies because it was simply designed mechanically correctly from the start. And that is why the Prius, and practically all other modern cars for that matter, are simply wrong. Period.
bruceha_2000 says:
08:16 AM, 11/ 2/10
First: Dan - If this car is misaligned, I suggest you get that fixed BEFORE writing up a 'this car's ESC is broken' post. Clearly you have not had this car since it was new. Someone whacked a curb or pothole HARD and didn't get it realigned or it has been in a frame bending accident and improperly repaired.
Second:
I just LOVE it when people who have never driven a car tell others how it works! :)
I have owned my 2004 Prius since the day it arrived on the dealer's lot in Sept 2004, it has 106K miles on it now. I live in NW Vermont, but not up in the hills. However, until 2 years ago, my in-laws lived up a steep hill in Stowe.
The TC is protecting the electric motor from over reving. It does seem like they could have some limiter rather than full cutout though.
To those posters who mentioned the overly sensitive traction control even on wet or sandy roads. Yes... and No. The OEM Goodyear Integrity tires are CR@P. If you haven't figured that out while driving, check the TireRack survey results. Very sad that Toyota couldn't spend another $100 total and get some decent tires on the car from the start. If you don't replace them soon after getting the car, buy some decent (and I do NOT mean performance) tires when the OEM's wear out and you will notice the difference in those situations IMMEDIATELY. My wife's cousin didn't like his '05 Prius for the exact same reason until we talked and he replaced the tires. Then he LOVED his Prius and still does.
If you live where there is real snow, get real snow tires (which you SHOULD do for ANY car). If you don't get too much snow, QUALITY all seasons with at least GOOD snow survey results.
With my lousy OEM tires only 3 months old and maybe 2,000 miles on them:
- Stopping at a stop sign on a slight down hill on a PLOWED street: wheels would stop turning and the tires would slide about a foot on the muck before coming to a stop. :O I could get the TC on even when starting slowly on similar stuff on a flat. Had to be VERY gentle on the accelerator to get started.
- Going up a relatively steep long driveway that HAD been plowed (maybe 1/2" packed snow and some mostly bare spots) and some speed (~10 MPH) going in, the TC kicked in but the car made it up.
- Going up from 0 MPH, the TC would stop the drive with the pedal to the floor. The car stopped (gravity) then SLID back down until the tires got traction and the car would str up the hill some more. Rinse and repeat for 100 yards until the hill flattened out. Remember this driveway HAD BEEN PLOWED!
I got some Goodyear TripleTreds the next week. Same hill, 4" - 6" UNPLOWED and UNTRACKED snow, with the plastic stickers still on the tires having been mounted 2 miles away:
- Starting with speed (~10 MPH) the car went up with some TC kick.
- Starting from 0 MPH, it would still come to a stop but it did NOT slide down. I had to take my foot off the accelerator so the car could ROLL back to a traction spot.
- Once the driveway was plowed, no TC at all from 10 MPH, slight TC from 0 MPH. HUGE difference.
The ONLY time I have gotten stuck was in a 'Century storm' - 29" in 22 hours. The plows couldn't keep up. Minimum ground clearance on this car is 4.9". MOST of the 10 mile trip home from work was in 6-8" of chewed up snow having to go around cars stuck all over the place. When the TC stopped the car, I backed up to get some speed on and 'plowed' ahead. If only there were a mini 'personal' plow for my car. Just enough to get the snow down to 4.5" would be fine. :) I made it a LOT farther in my Prius with 40K miles on the TripleTreds in that Valentine's Day storm than most cars (i.e. not trucks/high clearance 4WD SUVs) with true snow tires. Another 1/8 mile and I would have been home but the last 1/4 mile hadn't been plowed and was 12" deep.
Do not reject the Prius just because you live where it snows. Mine handles better in the snow than any car I have owned ('78 Celica Manual, '86 Mazda 626 manual, '95 Honda Odyssey automatic - all FWD). You don't lose momentum at shift points since there aren't any. Tortoise and the Hare - slow and steady (as you SHOULD be driving in the snow anyway) wins the race. My wife's prior car was a '97 Subaru Legacy AWD. She is perfectly happy driving her '06 Prius in the snow with the same Hakkapeliitta snow tires. 4WD/AWD is NOT necessary.
lzmperu says:
12:27 PM, 01/25/12
Hi, I have the exact problem with my 2004 Prius. Did you get it fixed?????
Thanks for your time.