Whining noise & brake failure after dead battery

Have had 4runners since the 90s, this 2007 for 8 years. Left the lights on and a door slightly ajar, so the lights didn't cut off automatically. Killed the battery. Jumped started and: Brake light is on and a loud whining noise! Never had this happen in all the years of owning a 4Runner!!! Brakes go to the floor, plenty of brake fluid. Disconnected the negative post 5 minutes, no change. Any ideas? Alternator?

 

Pump on the master cylinder/booster sounds like it's dry but I don't know why it would be on if there's no key in the ignition. Still, it's probably something about the master cylinder that's causing the problem if the reservoir is full. The pump is trying to pressurize the system and it can't so it just keeps pumping and drained the battery. Is there evidence of brake fluid under the car?

 

OK, will check out the master cylinder in the morning. No leaks anywhere. No issues before I killed the battery leaving the headlights on and a door ajar. This 4Runner has been problem free for 7 years (regular maintenance). The whining noise is high pitched. Could I have damaged something jumping the dead battery?

 

You wouldn't have hurt anything unless you crossed the polarity on the battery to the jumper cables.

I don't understand why the brake pump would be running if the ignition was off but the headlights were on. I know on my '04 if I leave the lift gate open the lights will go out after a while. I don't know about the other doors. The headlights go off after a short while too but I think you have to have the doors shut and locked.

Check where the whining noise is coming from. If it is the master cylinder and there's no leak under the car and the master cylinder is full then I would hazard a guess that there's a disconnect between the pump and motor, but I don't know why a jumpstart would have caused that. It's also a mystery as to why the brake pedal goes to the floor. I thought all cars had to have SOME brake capacity by means of dual brake lines.

 

Not sure why a dead battery would cause this issue....but the way the brakes work is there's a master cylinder ABS assembly, which has the master cylinder, a little electric motor which runs a pump which builds up and stores pressure in an accumulator.

When you turn on the ignition the motor comes on and runs for around 15+/- seconds to build up pressure in the accumulator, the same thing happens after about 3 depressions of the brake pedal as the pressure drops, you should hear a slight buzzing/electric motor sound coming from behind the speedometer area when the motor is running, all this is normal.

The pressure in the accumulator does 2 things, it's used to assist the master cylinder when you apply the brakes to give you "power brakes", it's also used by the ABS system to help control braking.

What you're describing sounds like there's no pressure in the accumulator which will trigger the brake warning light, it should also trigger an alarm, which you don't seem to be getting, with no pressure in the accumulator the brake pedal will go almost to the floor and feel very hard to press any further, you should still have some braking power but it will be very minimal and not stop you very good but the harder you press the pedal the more it will try and stop you...but I would advise not to drive it in this condition because it's very difficult to get the vehicle stopped.

I'm not sure what the buzzing sound you're hearing is unless it's the little electric motor trying to run but can't, you need to pinpoint where this buzzing is coming from, check to see if it's coming from the master cylinder/ABS assembly, use a long stick/broom handle, very long screwdriver or similar item and press it against your ear cupping your hand around it as you press it to your ear, touch the other end to surfaces in the area the sound seems to be coming from the broom handle will function like a stethoscope enabling you to pinpoint where the noise is louder/coming from, the electric motor/pump/accumulator assembly is at the back of the master cylinder where it attaches to the firewall.

Report back what you discover.

 

If you jumped it with the jumper cables grounding cable on the negative battery terminal there is a "slight" chance something was fried.. the grounding cable of is suppose to be attached to a metal point to ground it out.

 

"Somehow", jumping a dead battery fried the Brake Master Cylinder motor?

 

Have you disconnected the battery for 20 mins and reconnected to try to see if for some reason a reset would sort it out?

 

Now when you charge up the battery the master cylinder pump is running with the ignition off?

In addition to leaving the lights on and the door ajar did you leave the ignition on? I'm trying to figure out the scenario of what happened after you parked the car for the night. You said you left the door ajar and the headlights on but I would expect that the headlights would go out if the ignition was off and the only way the brake MC pump would be running was if the ignition was left on, which would leave the headlights on.

 

Makes no difference as there's a 4" body ground wire connecting the negative terminal to the fender. I suspect @ehanvey reversed the polarity of the jumper cables, which can get messy. Hopefully he hasn't fried any modules, which can exceed the value of a 17 year-old 4Runner.

 

99% sure I didn't cross cables because eventually the battery charged and cranked. Tried this morning and the battery was dead again. Bought a new battery. Waiting for the rain to stop.