Should ABS brakes cycling frequently?

just bought my 1st runner an 02 and real clean no rust runs great with 160500 on the odo.
So my question is this.....when I first start the truck I can hear the an elec motor located just below the master cylinder cycling for about 30 sec. then a relay from the front right (the other side from the abs) clicks and it goes off. I can make it do it again by pressing firm on the brake peddle a few times and it will do this continually. It will also come on while driving say 5 or 6 times over about 7 miles. especially when hilly. Is this normal? Anything to worry about? The brakes are solid and have a good hard peddle. I have pulled the wheels off and checked the wheel cylinders and have looked at the whole system over and don't see any leaks. It has an accumulator right next to the reservoir ad just above and to the right of the aforementioned elec motor but if nothing is leaking, after the motor builds the proper pressure where the hell is the pressure going? It always has a hard peddle and no drip spots in the garage or wet areas under truck?
PS brought it to toyota and had a flush and bleed.


Thanks fellow runners looking forward to a long run!
Tom

 

Hi Tom, and welcome to the site. This activity does NOT sound normal. For ANY vehicle. Has the vehicle been involved in any accident, or is the brake system losing fluid? I am wondering if the ABS system might be failing somehow. Check it out..

 

Haven't heard another word. Kinda normal around here for some reason.

 

I took it to toyota and had them flush and bleed it still no change. Its not leaking anywhere i can find its dry. never been in an accident as far as I know of Ill get some pics up soon. I relisted the question with more detail today not sure where it went?

 

What does that mean you bumped it for me?

 

Hi Tom, 'bumped' usually means that another reply was posted to a past thread, to bring it back up to the top of the thread list. Inactive threads sink toward the bottom of the list! I am wondering if your system uses an "accumulator", which is a hydraulic device that would "store" some volume of fluid/pressure in order to cycle the ABS in certain conditions. If so, I wonder if it is losing pressure when the vehicle is parked for a while, and is getting "pumped back up" when the vehicle is restarted.. I dunno but that would explain the lack of a wet spot on the floor.

 

Thanks for replying to me!
I had revamped my question and reposted it and then it just disappeared?
So I do believe it has an accumulator Its a gold cylinder right next to the master just above the elec motor im talking about.
It seems to cycle and build back up pressure very frequently.... every few minutes? I explained all this to toyota when I had the brakes bleed I had heard air in the system could do this did not get any better actually seems to be getting worse! what do you think I should do now?
Thanks, Tom

 

Hi Tom, sorry for the late reply. Have actually been asking people and researching to find out exactly how the system works before answering. So far, it looks like the consensus is that the accumulator is loosing pressure, the system is sensing this, and cycles the electric motor to rebuild the pressure to it's 'ready' state. What I find strange is that there is no ABS fault light showing. My gut thinks that the accumulator cannot be serviced separately, and that most likely you would be better off money wise to replace the entire sub-unit. I would also have whoever that I entrusted to do this to very carefully inspect the brake lines/ calipers for internal rust. This is another reason to semi- annually have your brake system flushed. Most likely the previous owner did not bother with this maintenance, thinking it was OK. Then water got in the system, rust hosed some internal check valve on the ABS.. (just a hypothesis) Best of luck on this- and please keep us posted on the outcome.

 

Thanks so much for your diligence, when I took the truck to toyota for a flush and bleed (I did not do it myself. after reading that you need a toyota computer to do it right AKA you do not pump the brakes or use air pressure to do it the computer uses this elec motor we are talking about to flush and bleed the system) They pulled up my vin and showed me the service history it has been done before. I wastold what came out was clean and had no water in it. Is there air in the accumulator that leaks out? If its just fluid would I not see it leaking out? Yes it is strange that the peddle is always firm there is no lights coming on the dash? Thank you again!

 

Hi Tom, Just had another thought. something you just said triggered a memory. Bear with me here. A well pump system has a storage tank that serves two purposes. The first is to store a volume of water to be used without the pump having to run, and the second is to tell the pump when to run. This system has a rubber diaphragm in the tank that separates the water from the air that tells the well pump when to cycle and build pressure back up. IF the diaphragm is ruptured, or the air pressure is set too low, the system will "short cycle" - Now to your ABS. The accumulator acts very similarly to the water storage tank, in that it has a ready supply of high pressure brake fluid at the ready in case of the need of ABS action. I believe that the ABS system does not use a rubber diaphragm/ air separator, but rather a metal diaphragm/ large spring/ with maybe N2 on the back side. Still, if the diaphragm is leaking, the charge pressure will be very 'peaked' instead of a 'plateau'. - And I would expect your system to behave as the well pump would.
It is interesting that the previous owner had this service performed. How recently, did they say? If it was fairly recent, makes me think that they knew something was wrong when they sold it.

 

If this is a closed system ..not like a well pump system ( witch I have on a house in NH. and have recently replaced) .......... Ah this is to much for a holiday weekend We can pick it up later The best to you and yours enjoy! It looks like I can pick up a complete unit warrantied (6 month) for around $400.00 then install it and have it bleed again. Its still working for now Hope the sun is shining where you are ...Talk soon

 

Hey Tom, just in time for another holiday, but what became of the ABS issue? Is it fixed yet, or are you still dealing with it?

 

You sound correct about the accumulator issue so if that whole thing needs to be replaced I figure I will use it till it breaks.There are no lights on the dash its got a great peddle and abs works fine so Ill roll with it for a while see what happens!

 

did toyota also bleed the abs master block where all the break lines go into.

 

because if the former owner cracked open the abs master block and tried to bleed the brakes from there that would most likely be the cause of your problems.

 

believe me i have seen people do this against my advice. some people rite.

 

Thanks so much for your diligence, when I took the truck to toyota for a flush and bleed (I did not do it myself. after reading that you need a toyota computer to do it right AKA you do not pump the brakes or use air pressure to do it the computer uses this elec motor we are talking about to flush and bleed the system) That being said I don't know what that entails if that block was bled or not? Why dose it have a good peddle and no lights on the dash?