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Toyota Avalon Brakes, ABS, VSC, etc.

147 messages,  Last post on Mar 05, 2009 at 7:31 AM

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#138 of 147 Re: ABS Failure -- Pedal to Floor [mermidon] by wwest Mar 02, 2009 (6:40 pm)
Replying to: mermidon (Mar 02, 2009 1:05 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 147 Re: ABS Failure -- Pedal to Floor [mermidon] by Mr_Shiftright HOST Mar 02, 2009 (7:06 pm)
Replying to: mermidon (Mar 02, 2009 1:05 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. Replies to this message: wwest (Mar 03, 2009 9:43 am) Mr_Shiftright (Mar 03, 2009 9:52 am) wwest (Mar 03, 2009 10:10 am)
#140 of 147 Re: ABS Failure -- Pedal to Floor [Mr_Shiftright] by wwest Mar 03, 2009 (9:43 am)
Replying to: Mr_Shiftright (Mar 02, 2009 7:06 pm) 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. Replies to this message: Mr_Shiftright (Mar 03, 2009 9:52 am) wwest (Mar 03, 2009 10:10 am)
#141 of 147 Re: ABS Failure -- Pedal to Floor [wwest] by Mr_Shiftright HOST Mar 03, 2009 (9:52 am)
Replying to: wwest (Mar 03, 2009 9:43 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. Replies to this message: wwest (Mar 03, 2009 10:10 am)
#142 of 147 Re: ABS Failure -- Pedal to Floor [Mr_Shiftright] by wwest Mar 03, 2009 (10:10 am)
Replying to: Mr_Shiftright (Mar 03, 2009 9:52 am) 100% sure..??   No, NEVER.   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 147 Re: ABS Failure -- Pedal to Floor [mermidon] by fin Mar 03, 2009 (5:15 pm)
Replying to: mermidon (Mar 02, 2009 1:05 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......? Replies to this message: wwest (Mar 04, 2009 5:54 am)
#144 of 147 Re: ABS Failure -- Pedal to Floor [fin] by wwest Mar 04, 2009 (5:54 am)
Replying to: fin (Mar 03, 2009 5:15 pm) "...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 147 Re: ABS Failure -- Pedal to Floor [mermidon] by amauhry Mar 04, 2009 (10:58 am)
Replying to: mermidon (Mar 02, 2009 1:05 pm) 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!   Amaury '08 Limited Replies to this message: wwest (Mar 05, 2009 7:31 am)
#146 of 147 Re: ABS Failure -- Pedal to Floor [amauhry] by wwest Mar 05, 2009 (7:31 am)
Replying to: amauhry (Mar 04, 2009 10:58 am) MIL and/or CEL is reserved for engine problems/emisisons.   ABS/EBD/VSC/etc will not cause an MIL.

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