Weird braking sensation on pedal

[Runner Up]

It's raining here today, so I'm getting all my questions out in rapid succession

When I'm driving at slow speeds in town, 80% of the time that I come to a set of traffic lights, 4-5 seconds before I come to a complete stop, I get a strange electronic noise and vibration in the brake pedal. It kind of feels like the ABS system is on the verge of kicking in, but it's not a true ABS sensation. In other words, it's less intense, and more of a constant vibration than the typical intense pulsation that you get from the ABS when you brake hard on snow and ice.

My ABS light comes on at ignition, but quickly goes out the same as all the other dash lights upon ignition.

Anyone else experience this, or know why it's doing that? Is this the ABS system telling me that my brake pads are due for replacement?

 

[MarkinWMich]

Mine has done that since I bought it in 2008. Mine is a more or less intermittent, usually first thing in the morning or when its cold outside. It's had a few sets of rotors and pads since then. I've got new rotors and pads on mine (a few weeks ago), and it did it this morning. I believe it is the ABS system, and I think it is normal behavior.

The ABS "idiot light" comes on and then off, along with several others, when you first trigger the ignition. I don't think there is anything to worry about.

 

[nevada]

I think what you are feeling is the abs pump pressurizing the accumulator. which is where you get you power assist from. pressurized brake fluid.

in itself, its normal. but I think if its happening too frequently, you may have an issue with an internal leak that is bleeding off the pressure.
USUALLY this type of thing is just a lead up to having to replace the MC.

but, as can be seen above, that's not always the case.

 

[bpowa]

mines does this also. almost a buzz on the brake pedal. I thought it was the abs module. Now the more I drive it. I think its the fan clutch kicking in.

 

[Runner Up]

mines does this also. almost a buzz on the brake pedal. I thought it was the abs module. Now the more I drive it. I think its the fan clutch kicking in.

I was starting to think it was the fan clutch as well, but it's not. When I come to a stop light, I get the brake buzz/vibration, and then it subsideds, and then the fan clutch kicks in. They sound and feel similar, and occur one after the other, but they are two distinct issues, at least on my rig.

The previous owner indicated that he had recently replaced the brakes, but I do find them to be soft. I have a feeling that Nevada is correct. I have a feeling that the ABS pump is working overtime, but the presure is bleeding off somewhere, which may mean that the master cylinder is on its way out.

 

[tysauce]

Could it be the traction control system? In my user Manual for my 2007, under the Traction Control heading, it says, "You may feel vibration or noise in your vehicle, caused by operation of the brakes. This indicates the system is functioning properly."

 

[KingPrat]

I would have to agree with the ABS accumulator. Pretty normal, unless it's happening every time you hit the brakes.

If the previous owner did brakes himself, I would have them bled to try to fix pedal feel. If that doesn't fix the issue, be sure to take a deep breath before reading how much the pump costs...

 

[m85476585]

It sounds like the ABS pump. Mine comes on just about every time I press the brakes, and if I've been holding the brakes for a while, like at a light, it comes on again for a bit, though I might not be holding the exact same pressure on the pedal the whole time. As far as I know that's normal. If you press the brakes a few times when the car is off, it uses up the accumulated assist. If you press the brakes while the car is on it uses up some of the accumulated assist, so the pump comes on to replace it. Our trucks don't use vacuum assist like a lot of cars do.

If it was running all the time or couldn't keep up with demand that would be bad.

 

[SanDeggo]

Try turning off your traction control for a trip and it will likely be gone. If that doesn't do it, I'm not sure what it could be.

 

[Runner Up]

Try turning off your traction control for a trip and it will likely be gone. If that doesn't do it, I'm not sure what it could be.

I'm not sure that I have Traction Control. Mine is 4x4. Can I turn it off?

 

[m85476585]

I think all the 4th gens have it. Some of them (2008 and newer?) have a switch to turn it off called VSC Off, otherwise you can lock the center differential to turn it off (not recommended on dry pavement). But if traction control comes on you'll know it. Vibration is an understatement; it is more like a jackhammer. What you described still sounds to me like the ABS pump working normally to give you power brake assist.

 

[tysauce]

Ya after doing more research it seems that it is the brake booster behind the firewall and is completely normal. Unless it gets progressively worse, I don't think it's anything to worry about.

 

[SanDeggo]

I'm not sure that I have Traction Control. Mine is 4x4. Can I turn it off?

This is the switch that I have in my 4Runner. Long story short though, what you are experiencing is completely normal. I've had it happen to me a few times, it is just the ABS pumping to regain traction to the tires.

 

[nevada]

This is the switch that I have in my 4Runner. Long story short though, what you are experiencing is completely normal. I've had it happen to me a few times, it is just the ABS pumping to regain traction to the tires.

no.
it is the ABS pump recharging the accumulator. which is what is used for the power assist.

 

[SanDeggo]

no.
it is the ABS pump recharging the accumulator. which is what is used for the power assist.

Correct me if I'm wrong, but the ABS will recharge the accumulator because traction control has been activated. At least that is certainly the way that I have understood it and the only time I have ever lost traction is when that vibration in the brake pedal takes place, which would not happen if I turned my traction control off.

 

[nevada]

Correct me if I'm wrong, but the ABS will recharge the accumulator because traction control has been activated. At least that is certainly the way that I have understood it and the only time I have ever lost traction is when that vibration in the brake pedal takes place, which would not happen if I turned my traction control off.

it will do it then ALSO. but the pressurized fluid is where the power assist comes from, so its being USED up every time you push the brakes. eventually, it will have to be recharged, even if the abs never activates.

 

[RPS13]

The ABS motor is separate from the assist pump correct?

You can turn the key to ON (engine off) and hit the brake pedal and you'll usually feel/hear the same thing.

 

[BlackWorksInc]

Correct me if I'm wrong, but the ABS will recharge the accumulator because traction control has been activated. At least that is certainly the way that I have understood it and the only time I have ever lost traction is when that vibration in the brake pedal takes place, which would not happen if I turned my traction control off.

The pump kicks on when when the pressure gets to its pre-set minimum threshold. When the Skid Control ECU decides to kick the pump on, it turns it on (which means during operation and just normal use and at start-up, ect.)

The ABS motor is separate from the assist pump correct?

You can turn the key to ON (engine off) and hit the brake pedal and you'll usually feel/hear the same thing.

Its all one unit, the physical pump is located on the bottom of assembly and is responsible for hydraulic pressure; the tank on the side is for storage.

 

[RPS13]

So there's no separate ABS motor for pulsing each circuit vs. the hydraulic assist unit? I know it's all one subassembly, but there are different motors on it last I looked.


The 4th gen 4Runner ABS is pretty crappy IMO, but I could just be spoiled coming from more sporty cars. It keeps the wheels turning, but it engages too soon, and it tends to not let up when the brakes are released (bad news when you're trying to actually move forward some to not have the girl texting behind you slam into the back of you).

 

[BlackWorksInc]

So there's no separate ABS motor for pulsing each circuit vs. the hydraulic assist unit? I know it's all one subassembly, but there are different motors on it last I looked.


The 4th gen 4Runner ABS is pretty crappy IMO, but I could just be spoiled coming from more sporty cars. It keeps the wheels turning, but it engages too soon, and it tends to not let up when the brakes are released (bad news when you're trying to actually move forward some to not have the girl texting behind you slam into the back of you).

Well Toyota set-up more for an SUV than a sports car, so it doesn't surprise me if its a bit aggressive; the common trend in the industry is to just have the car do everything for you because 95% of people can't or won't learn how to be a responsible human being and operate their vehicles correctly.

What you are referring to are "Solenoids" not motors, the Solenoid Pack is located on the side of the master cylinder inside the big black plastic box that also houses the Skid Control ECU (on pre-'05 units the Skid & ABS ECUs were split up if I remember.)

The main difference from a solenoid and a motor is that a motor rotates, a solenoid moves in and out. i.e. door lock actuator, fuel injector, shift solenoid, ect.