*HELP!* Brake Pressure light on

[LT1Vettepilot]

1996 LT1
While driving around this morning, I stopped to go into a shop and when I came back out a drove away, about the 4th time I applied the brakes, my "BRAKE PRESSURE" light came on. I pulled over and opened the hood to check the brake fluid level, vaccum connection, and any electrical connections to the brake booster. The level is good, vaccum hose is in great shape, but I can't find any obvious electrical connections to the booster. I don't know a whole lot about this braking system (my last car didn't have ABS). I looked under the car and can't find any leaks. The brakes feel fine, I even tried a few hard braking applications on my way back to the house. No fade, stops fine, ABS works fine. If I shut off the car and wait a few seconds and turn the ignition back on, the "BRAKE PRESSURE" light comes on bright like its supposed to when the engine is first started and then tries to go out, but only dims and then gradually gets bright again, taking about 2-3 seconds to come fully on. Seems like the light is tide into a varible resistance pressure switch, i.e. the reason the light is gradual.
I checked the parking brake and it works fine as well, and of course has its own advisory light. The owner's manual of course just says to take the vehicle in for service. Being Saturday, none of the dealer's service centers are open. What else should I be checking? Where is the brake computer? Where is the pressure switch? If any of the brake pads are worn too far, would the computer sense the extra movement required and turn on the light?
I did wash the car yesterday, including under the hood. I'm going to check all the connections I can find and blow any water out of them with compressed air.
The Corvette is my daily driver, and only vehicle, so any help I can get is greatly appreciated! Thanks

Mike

 

[vigman]

Poll the CCM!

See what it thinks the problem is.

Mike

 

[vigman]

Procedure ( reposted )WILL NOT WORK FOR 96!!

Never mind
1996 ODB II
This will not work..sorry!




You can pole the CCM and get the error codes for the ABS/ASR system

TURN OFF KEY..FIND ALDL CONNECTOR
(UNDER DASH LOWER THAN YOU KNEE WOULD BE)

To read the CCM
Make sure the ASR light is OFF before doing this
Key Off
Have pen & paper ready
Jump pins a & g in tha ALDL connector paperclip will do (Top left A bottom right G)
turn key on
This will start the Auto diag of the CCM
The numbers where the speedo lives will give you codes eg C 51 or H 51
(the C means current H means History)
and below there will be another number
( eg 1.1, 2.1 etc)
These will tell you the MODULE at fault.
9.0 is the one of interest I believe.
Write this info down
Repeat as needed
To exit
Key off

Post this info..
Mike

 

[vigman]

More thoughts

The EBTCM module
Electronic Brake & traction control module
Isn't that a mouthful!

Is not shown on my 93 book.. but the computer TYPICALLY just pulls a transistor to ground to light the light, the fade thing has me concerned
since the sensors go into the computer directly, and the outputs are indivdually controlled.

In the digital world things ( should be ) either on or off!

will look in a C-5 book for more insight!

Mike

 

[LT1Vettepilot]

UPDATE

Everything checks out visually...no damaged wires, hoses, lines, no water in any connections. In the time it took me to post the first message and go back to the car, the light no longer comes on after the initial test phase.
I found the ALDL connector, but it isn't labeled with pin identity, the owner's manual has nothing about it at all, and I don't have a Haynes or Chilton's on the car...*YET*
Since the standard practice for pulling codes doesn't work, I guess it doesn't matter than I found.
So I took the car out on the street and did some quick accel, decel runs and had no problems. ABS worked fine, car stopped. I tried power braking it with ASR on and off. With ASR on, everything worked properly, no brake pressure light. ASR off I got expected wheel spin let off brake and reapplied-car accelerated and stopped as demanded. Light has not come back on.
I pulled the hydraulic brake fuse in engine bay (after the light had already gone off) and it was good.
As far as the digital world of electronics goes, if the switch runs off of a transistor, then the transistor may be switching on and off very rapidly, this would appear as a gradual increase in the light's intensity. Not sure though, been several years since I've dealt directly with digital electronics.
When did the OBDII first take over? It was '96 right. That figures
If the light stays off, then some time next week when I've got a chance, I'll take it to the dealership and talk with their Corvette Specialist (yes, I'm that lucky to have a dealership with a Corvette specialist on the pay roll...he's built several daily driver vette's with 450-650HP and one very streetable 750HP one!!!!!!).
Hopefully I won't have to pay the $60 an hour for him to hook up his handy dandy computer and tell me whats wrong.
Thanks for the info

 

[vigman]

ODB 2

95??!!!! I think.

Yes, have it tested to see what the history was..might give a clue to the failures.

Sorry about the confusion.. still getting my electronic year / brake points down.

The eveloution(sp) of different sub systems is interesting to track.. and how they retrofit & modify make it all so .....whats the word im looking for

Confusing..no challenging!

Yea that's it

Mike

 

[LT1Vettepilot]

PROBLEM SOLVED!

Well I've found the culprit! It was a loose connection at the pressure sensor attached to the bottom side of the master cylinder. I completely missed that connection! My room mate is an old school mechanic, hates all the new electronics stuff, but knew about this switch that started being installed in the '70s. Went out to the car found the switch right away. A little jiggle on the wire and the light came on and went out. Just cleaned up the connetor and all is fine now. Guess I won't be needing to see the service center this week. Thanks for the help

 

[korea]

What a great site here !

Thanks Lot..

I had a same problem about "Brake pressure Light "above .
Finally I got a fixed just before.
I just dry out after unplug connecter bottom of Master cylinder


Thank for your post.

From kim