Engine Off, pumping brakes never gets stiff.

Hi, awhile back I had a close call with a vehicle merging into my lane. I had to brake really hard and noticed my brakes grinding aggressively and 4Runner had difficulty stopping, barely avoided a collision.

Today, I was checking my brakes and noticed a problem. When the engine is off, my brakes do not stiffen when pumping them. Is this normal behavior?

When the engine is on another odd behavior happens, I’m pumping the brakes several times while parked and a warning comes up saying pre-collision system failure please contact your local Toyota dealer.

Does anyone else have these issues, I have a 2023 4Runner ORP.

Thanks

 

If your brakes don't stiffen when pumping them with the engine off, it's usually normal because the brake booster, which relies on engine vacuum to assist with brake pedal pressure, isn't functioning without the engine running, making the pedal feel harder and requiring more effort to press.

Key points to remember:

• Vacuum-assisted brakes:
  Most modern cars use a vacuum booster that helps amplify the force applied to the brake pedal when the engine is running, resulting in a softer pedal feel.
  
  
• Engine off = no vacuum:
  When the engine is off, there's no vacuum to assist the brakes, so the pedal will naturally feel harder and require more pressure to engage.
  

When to worry:

• Spongy pedal even with engine on:
  If your brakes feel soft or spongy even when the engine is running, it could indicate issues like air in the brake lines, worn brake pads, a failing master cylinder, or a leaking brake line, and should be inspected by a mechanic.
  
  
• Sudden loss of braking power:
  If you experience a sudden drop in braking power with the engine running, this could be a sign of a serious brake system problem and needs immediate attention.

 

That’s the problem. The brakes are not getting hard when the vehicle is off. I have the same travel distance when stepping on the brakes whether the vehicle is on or off

 

The power brakes on late 3rd Gens and up to the newest T4Rs do not use vacuum assist brakes, these brakes now and have for many years uses an electric motor ran pump to build up pressure stored in an accumulator to assist in the braking action and to supply pressure to the ABS system.

 

Thank you, I thought I had a leak somewhere. I couldn’t get a straight answer from google.

 

With the engine off, and the brake is depressed, you should hear that motor run to pressurize the brakes. Are you not hearing the electric motor run?

 

Not sure if you saw my post about these brakes aren't vacuum assisted.

If you have a leak in the assist part of the braking system that affects braking action you would have the brake light coming on along with an alarm, your problem is most likely not the assist part of the system.

 

Are you under warranty? If the warning on the dash doesn’t go away, take a picture of it and show it to the dealer.

As far as the rest of your post, It’s hard to tell if your brakes have a problem or not, based on your description. It’s a brand new car, so it would be surprising if something is wrong.

If you were about to collide with a vehicle, and you slam your brakes as hard as possible, the anti-lock brake system will usually start to pulse the brakes to keep the tires from skidding. The hydraulic pulsing from the abs can be very loud and can sound like grinding. That’s normal during hard braking whenever the tires are about to lose traction.

A side effect of ABS activation is that sometimes all the pulsing makes it feel like you are losing braking effectiveness, especially if the road is slippery. In reality, the brakes feel less effective because there isn’t enough traction to stop as fast as you want to.

 

Well, disregard this comment. I could swear I have heard the motor come on when the brake pedal is pressed with the engine off. Try as I might, it did not happen. I did not cycle the brake pedal to several times to see if I could deplete the pressure, but, I did not notice a difference in the brake pedal. It is a hard pedal though when the engine is off.

 

The motor will come on with the engine not running...but the ignition does have to be in the "on" position to send power to the motor once the pressure is depleted.

 

That makes sense - I tried with the engine off, ignition on, pumped several times and didn't hear anything. And, of course, tried it with the ignition off, heard nothing again with several pumps of the brake pedal.

My 2015 Tacoma TRD Sport has brake boost... maybe that is where I heard the motor come on.

 

OPs problem could be some air trapped in the ABS system.

 

It usually only take 3 to 4 depressions of the brake pedal to trigger the motor....but in the shop manual it does say to completely deplete the pressure to do 20 or more depressions so it could take more than 3 to 4