2001 vert, as soon as i hit the brake pedal it locks up all the way and stays locked even if i try to accelarate! (with my foot off the brake pedal).
unlocks only after the engine is shut off.
cant use the car and not sure what to do, anyone has this problem ever?
problem goes away, with abs disconnected

 

Your explanation isn't too clear ....

What's locking ???

Your locking the tires and skidding ???

The brake pedal is staying down after you push it ???

If the pedal is staying down, are the brakes on or off after you release the brake pedal ???

Sounds like the brake pedal return spring may have come loose or broken, have you looked at that?? Though why disconnecting the ABS would affect anything doesn't make sense ?

 

as soon as i touch the brake pedal even at very low speed, the brakes act as if i am holding the brake pedal fully down, and even if i release the actual brake pedal, the brakes remain fully applied, only with a lot of accelaration the car etches ahead, still with the brakes fully applied (again not by the brake pedal i have already released it) i have never had or heard of this problem before, and don't know what to do.

 

Sounds like the EBCM is failing.

Check for codes (see https://www.corvetteforum.com/techti...D=26&TopicID=1

if you don't know how to display them, and post them here. You are especially looking for codes that are C codes rather than H codes.

A code looks something like this ..... B0401 C or C1201 H

The letter at the end shows whether the code is Current or History.

 

thats the biggest mistery of this all, there are no codes!
could the ebcm fail, without the computer detecting?

 

May have brake fluid contamination. Check the brake fluid. When removing the cap on the master cylinder look at the rubber on the cap, if it is deformed or swelled up in any way you have contamination in the brake system. Has anyone added fluid into the master cylinder?

 

I don't see how it could fail like that with no codes. Are you sure you're following the procedure given above for displaying codes? It is rare for a Vette to have no codes (History) stored. The EBCM doesn't generate brake pressure until it decides that at least one wheel is locking up. Even then, it "pulses" the pressure, it doesn't generate pressure and hold it.

If you're sure you're showing no codes, then I'd suspect the master cylinder, except you're stating that

A) turning the car off solves the problem

B) turning off ABS (how're you doing that?) solves the problem.

If A and B are true, then sounds like time for the EBCM to be looked at. Replacing the mechanical side of the BCM requires a Tech2 scanner to perform a purge of air from the system, so unless you have access to a Tech2 I'd starting making an appointment at a shop that you trust to do the work.

 

Try pulling the EBTCM module fuses. See if the problem still happens. Are you sure all four wheels are locking up?? You could have a pinched or damaged rubber brake line on one of the wheels. If it is damaged it will (AHHH SKIP THAT)!! You stated that if you turn off the car it resets! I would try to flush the system with clean fresh DOT4 fluid and see what happens. Still try to see exactly what wheels are being effected by jacking up the car on all fours and applying the brakes.

BC

 

 

car is in the shop already more than a week with no solution all grounds and electronics check out ok, and like i said there is no codes

mechanic says it might be the abs (brake) pump.

 

I disagree with the diagnostic result!!!
Well,,,,, riddle me this MR. GM service tech. If you disconnect the "electrical" portion of the system and the problem GOES AWAY,,,how can it be the mechanical side of the system??????????????

I would be more willing to say that the EBTCM side of the system is the problem. With the ELECTRICAL side of the system out of the picture it works or should I say "IT DOESN'T LOCK UP".

I'm just trying to stay of the "EASTER EGG" parts replacement game and try to save you some bucks. Talk the problem over with the service adviser and see what he says. Theres always more than one side of the story and sometimes,,, there is critical information left out of the conversations.

Let us know what you figure out. I'm interested!

Bill C

 

In addition to the electrical side of things, this is one area I would explore as well. If the master cylinder is preventing the fluid from returning to the reservoir, or if there is sufficient swelling inside the rubber brake hoses allowing them to effectively become "check valves" and impede the reverse flow of the fluid too.
All of these particular symptoms may be caused by, or at the very least aggravated by, any rubber part in the entire system that has swollen due to contamination.
Keep us posted on your progress.
Robert
BTW, Bill Curlee:
Isn't there some rubber components inside the BPMV? Around the valves maybe?

 

Ive never had the opportunity to disassemble one but I would be willing to bet that there is some rubber or rubber type of software in there. The weird part is,,,,everything works without LOCK UP when the electrical side is out of the equation.! If it were mechanical (BPMV, hose, wheel Cyl, proportioning valve etc ect... it would lock up all the time.

BC

 

LonestarFRC and (if I may call you that) Bill,

Here's my thinking on this ... tell me where I'm off track ....

Assuming C5FLORIDA is correct (and there is no reason to believe he isn't) then disabling the electronic side of the system makes the problem go away ... so ...

Mechanical brake system is working. There are no kinks in lines, bad fluid, master cylinder issues, etc.

So problem has to be in the EBCM ... but it seems weird that it isn't throwing codes ....

C5FLORIDA applies brake with EBCM enabled (disabled, again, no problem) and the brakes "lock" and stay "locked". This would lead me to believe that several things have to be happening within the EBCM itself.

First, it has to be making a "bad" decision that one or more wheels are "locking" when they aren't.

Second, it has to be then commanding ON the pump to allow it to pulse brake fluid to one or more calipers where it "thinks" there is wheel lock occuring.

Finally, it is unable to "pulse" the brakes and instead is pressurizing the lines to one or more calipers and not releasing the pressure.

BUT, if the EBCM is getting a false "wheel is locked" signal, wouldn't it first want to RELEASE pressure on that caliper, rather than put more on it?? Instead it seems to be adding pressure to the system .... HEY .. could the EBCM be getting a false "WHEEL LOCKED" signal from one wheel, be REDUCING pressure on that wheel, yet be INCREASING pressure to the other three "good" wheels????? If it's doing that then C5FLORIDA would think that the car is "braking" when he has his foot off the brake, and the EBCM thinks "I'm doing the right thing, I'm reducing pressure on one caliper and braking the s**t out of the remaining 3 ????? The EBCM wouldn't throw codes because it believes it is "doing the right thing" ... like certain politicians out there ???

Could a bad wheel speed sensor cause this ??? OR a bad signal from a wheel speed sensor (due to glitches in the wiring) cause this??

I would look at the wheel speed sensor input using a Tech2 scanner to see if the EBCM is getting a "bad" or "false" reading.

Your response(s) are looked forward to with fear and trepidation ...

Steve

 

Steve

Great post!! The 2001+ EBTCM are mini computers and preform some pretty complex stuff really quick. Its not very difficult for it to get whacked out! When mine went bad, it would apply all four brakes in the pulsed brake mode while the car was driving down a perfectly straight flat and smooth road. The wife told me that it was doing this and I told her that she was crazy!!!!

I get that run up my A$$ quite frequently!

Checking the wheel speed sensor outputs from all four sensors is a snap! Just unplug the main connector from the EBTCM and probe the pins that correlate to each wheel. You should be able to read the correct resistance and also an AC signal in millivolts that increases as wheel speed increases.

My problem is why would it read NORMALLY until he taps the breaks? If it were a faulty wheel speed signal,,,,,it would throw the DTC for that wheel as soon as the car moves a few feet.

I would suspect that the EBTCM is corrupt and needs to be replaced. If it were me,,,I would get a re-manufactured unit off the INTERNET for $450 that comes with a "LIFETIME" warranty.

Thanks

Bill C

 

Bill,

Thank you for the complement. It also dawned on me later (duhhh ...) that when C5FLORIDA releases the brake pedal the EBCM should command the pump OFF and let the brake system return to its "normal" non-pressurized state. The EBCM seems to not be doing that.

Then I thought "well maybe the problem is in the sensor that determines whether the brake pedal is in the ON or OFF position", but then thinking hard (my head hurts when I do this kind of thing ) I realized that if that sensor (switch) was bad then, as you point out, why does the brake system act normally up until the brake pedal is steppped on?

Gotta be the EBCM ... but why no codes ??? Is it so effed up that it doesn't even realize it is effed up ?? I've been in the computer industry for a LONG time and it isn't hard to believe that a software/hardware glitch is occurring that the computer itself doesn't recognize it has a problem. Hopefully GM is looking at cases like this and further "tuning" the software to recognize these kinds of situations.

Bill, I think you hit the nail on the head in recommending the EBCM be replaced.

Steve

 

C5FLORIDA

Contact GM Customer Assistance, tell them your plight and see if they Will lend you a hand with the cost of the module replacement! I know it sounds strange but, you never know. They helped me and a whole bunch of other people with the repairs. MAKE SURE that you tell them that IT is a SAFETY ISSUE!! Hea,,all they can say is no and you might get a YES!!

Let us know how you make out. The number is in your owners manual.

BC

 

Lot's of good advice here. Here's hoping you get this thing ironed out and soon. I just hope it doesn't turn out to be a compound problem of both a mechanical and electrical nature.
Like Bill said, keep us posted.

 

GM Tech says, it might be an issue with the anti theft programm (altho the security light does not light up when this happens ) that is governed by the BCM, not the EBCM, they will flash (reprogram) the BCM tommarow morning, so i will keep you updated.

Does this make sense to you?

 

WOW ..... I'd not argue with GM Tech .... but DARN that's scary if true .... the Security system can use (or cause) the EBCM to put the brakes on the car !?!?!?!?



PLEASE keep us posted !!!

Thanks,

Steve