Last post on Apr 05, 2012 at 2:08 PM
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Toyota Avalon, Brakes, Sedan
#137 of 175 ABS Failure -- Pedal to Floor
Mar 02, 2009 (1:05 pm)
This morning I had a bizarre situation with my 2007 Toyota Avalon. My community received 1-2 inches of a dry snow overnight. I left my home prior to a snow plow showing up and needed to travel down several small hills to leave the development.
To say the least, the road was slick. So I kept my speed to about 5-10 MPH. On four separate occassions while traveling this 3/4 mile stretch, my ABS system failed on me. On each occasion, the ABS kicked in and was pumping like mad. After pumping for what was probably several long seconds, the brake pedal would sink to the floor. During these events, my car did not feel as if it was decelerating at all. And of course, once the brakes hit the floor, I had absolutely no braking ability.
Please note that I was not manually pumping the brake, but letting the ABS system do its job. In addition, I don't believe I lost the ability to steer the car, although steering was incredibly tough since the roads were so slick.
I was finally able to get down the various hills by mainly hitting up against curbs (and fortunately missing mailboxes and telephone poles along the way). Once I got to the main road (which was plowed), my brakes appeared to work fine. So I continued to work since trying to head back to my house up those snow covered hills didn't appear to be a good option.
The local Toyato dealer was kind enough to get me an appointment within the hour of my call to them. However, they were unable to find anything wrong with the brake system. They tried to simulate the ABS failure in a snow covered parking lot (which was several hours after my event...and thus the snow was at least starting to melt and turn into slop). Of course, they couldn't recreate the failure, but instead confirmed that the ABS system was working as intended. They also ran diagnostics, which showed that no ABS failure code was recorded in the system. Lastly, they called Toyota corporate who claims that no one else had reported a similar situation.
Of course, my car was out of alignment due to my curb riding. So I left with a $85 bill for an alignment along with the "call us if it happens again". I asked the service manager if he knew what he was asking me to do -- wait until the brakes fail again and hope that I'm still around to talk to them about it.
To say the least, I probably won't ever buy another Toyota. Not sure how long I'm going to hang on to this one either...which I also use to transport my family in. So much for their safety rating in my book.
I appreciate all advice, tips and suggestions!
#138 of 175 Re: ABS Failure -- Pedal to Floor [mermidon]
Mar 02, 2009 (6:40 pm)
The ABS' brake pressure sustaining pumpmotor is just a 12 volt DC fractional HP motor very much like your windshield wiper drive motor. This is the very same motor also used for TCS, VSC, EBD, and BA functionality.
If you read the owners manual carefully you will find that these other functions have a time out delay to prevent overheating of this pumpmotor. What the manufacturers do not seem to be willing to say, admit, is the ABS functionality has this very same limitation, if the pumpmotor begins to overheat then you will lose ABS capability .
If you happened to start out the morning with anything less than an absolutely FULL battery charge then even the WORSE. I would also clean and burnish the battery posts/terminals/connections as just a bit if additional insurance.
#139 of 175 Re: ABS Failure -- Pedal to Floor [mermidon]
by MrShift@Edmunds HOST
Mar 02, 2009 (7:06 pm)
If you didn't lose hydraulic fluid I can't really understand how this could happen. I could understand a loss of vacuum to the power brake, giving you a very HARD pedal that might feel like loss of brakes.
#140 of 175 Re: ABS Failure -- Pedal to Floor [Mr_Shiftright]
Mar 03, 2009 (9:43 am)
When ABS activates to prevent wheel lockup/skid it releases brake pressure fluid back into the reservoir at/from the individual brake calipers. If the ABS pumpmotor cannot keep up with the rate of brake fluid pressure depletion due to ABS then the pedal will go (slowly...??) to the floor since the "makeup" fluid pressure must now come from the master cylinder.
That could be the result of a low battery, poor battery positive and/or negative connections, poor connections to the ABS pumpmotor, or a "tired" ABS pumpmotor. Most modern day vehicles have a time-out system to prevent the prolonged use of the ABS pumpmotor in support of other, ancillary, functions such as TC, VSC, EBD, and BA. Basically "reserving" some portion of the ABS pumpmotor for its primary purpose/use.
If some of these ancillary functions were highly active just prior to the need for ABS it is entirely possible that ABS capability would be foreshortened accordingly. And given the conditions stated it seems highly probable that TC would have been in use and maybe even VSC.
The ABS pumpmotor very likely has a permanent magnet rotor and it doesn't take many overheating cycles to compromise the magnetic aspects of the rotor. Therefore a weakened pumpmotor functionality.
#141 of 175 Re: ABS Failure -- Pedal to Floor [wwest]
by MrShift@Edmunds HOST
Mar 03, 2009 (9:52 am)
Really??!! Are you 100% sure about this? I'm....shocked...that this could be a default position for an ABS failure.
Got any links for this? I need to know more about it.
#142 of 175 Re: ABS Failure -- Pedal to Floor [Mr_Shiftright]
Mar 03, 2009 (10:10 am)
The problem could also have been a bit of debris blocking one of the ABS fluid pressure solenoid relief valves open slightly. Debris "washed" away, nothing for the techies to find wrong with the ABS.
But my experience has been that an ABS failure light indication is often the very first indication that I need to replace a failing 12 volt battery. The ABS pumpmotor self-test puts a VERY heavy load on the 12 volt power source and distribution system and if the battery is even slightly marginal.....
#143 of 175 Re: ABS Failure -- Pedal to Floor [mermidon]
Mar 03, 2009 (5:15 pm)
You have answered your own question: ...but instead confirmed that the ABS system was working as intended. They also ran diagnostics, which showed that no ABS failure code was recorded in the system.
So, it was working as intended and it failed..but... it passed! This example is more proof that modern auto electronic systems are simply far too complicated. Scary trip. This should not happen in a modern sedan.
But then, you never lost control of the car. An ABS working well gives you control as the wheels don't lock. Same for skid control. You might not stop but you go where you steer. These systems generally override any manual input. The sinking pedal allows this to happen within the systems therefore no error code. Probably.
It may be as *wwest* has described it above. Electrical current is critical to the modern auto. A voltage drop could slow the response time and maybe still not show an error. In any case, you are along for the ride. This might happen in any ABS/VSC car depending on the system settings, electronics, etc. ....Where is my 1959 Buick......?
#144 of 175 Re: ABS Failure -- Pedal to Floor [fin]
Mar 04, 2009 (5:54 am)
"...Where is my 1959 Buick....?"
Either in the junk yard or already melted down as scrap..
Exactly where it should be.
The way I remember it cars of that era were more prone to brake pedal "fade" for a myriad of reasons. Blown master cylinder seal being the most common but not far above on eof the 4 brake shoe pistons.
#145 of 175 Re: ABS Failure -- Pedal to Floor [mermidon]
Mar 04, 2009 (10:58 am)
But my experience has been that an ABS failure light indication is often the very first indication that I need to replace a failing 12 volt battery
As wwest indirectly pointed out, if the system is over/short of voltage for whatever reason you should get a MIL in the dash along with a trouble code stored in memory. A MIL and corresponding DTC should appear for any abnormalities in the system (ABS, EBD, BA, VSC, etc.). What happened to “mermidon” was completely out of wack, especially for the fact that the tests done by the mechanic showed no symptoms at all. mermidon didn’t mention, however, if he noticed any warning beeps and/or lights in the dash just prior to the incident.
My two cents: pay attention to the dash when starting your car. If any of the brake system icons don’t clear a couple of second after ignition, leave your car where it is and jump out of there!
#146 of 175 Re: ABS Failure -- Pedal to Floor [amauhry]
Mar 05, 2009 (7:31 am)
MIL and/or CEL is reserved for engine problems/emisisons.
ABS/EBD/VSC/etc will not cause an MIL.