So on my drive to work today my gs started beeping really loud and continuously, noticed the brake light was on the dash. I pulled over, turned the car off and back on, no change. I then checked my brake line connections for leaks and had nothing. Checked my master cylinder and fluid level was good, float also seems ok. I also checked the parking brake release cable and everything was fine. Seemingly happened with no warning signs. I recently did the ls400 brake upgrade so pads/rotors/calipers are all new. Thinking its my abs motor relay, but not sure what else i can check. Ive tried everything i can find related to it on the forums and havnt seen anyone with the same symptoms as me. Am i headed in the right direction or is there anything else i can try/test before replacing the whole master cylinder.

 

so i was able to take a look at it after work and grab some fault codes. main one im seeing thats the issue is a c1251 and c1256. peddle is hard as a rock pump is not working at all. what are higher chances of it being fuses or bad masterbrake cylinder/booster. I have access to the wiring diagram. and before i cleared the codes to see what came back immediately i did get a C1251 bad battery voltage code. i have a spare battery i can also test with. any help or which direction to start would be greatly appreciated!

 

So is it beeping and buzzing? If you can take a short video of what’s going on, i could confirm if it’s a bad ABS module or brake booster

 

its a constant buzzing exactly like this video here . cant take a video of my own atm since im not home.

 

Sounds like you have figured out the culprit, you might find a simple problem with the wiring or something like that, you can get a wiring diagram and test the wire plug just to make sure everything is everything, but your likely going to need to replace the ABS module/brake booster. Unless there is anything else that you suspect? Have you done any other work on the braking system recently? Another possible culprit is the brakes were bled incorrectly when you were installing the new front calipers. You might look for a forum that gives you the step by step instructions for bleeding the brake system, if you didn’t do that before?

 

was able to get a new booster/master cylinder at a local pull apart yard. swapped it in today and bled the brake system. pump on the new unit is definitely working now and i can hear it activate when the car is in the on position. the buzzing/beeping continued through the bleed until the last caliper was finished. after i finished the last caliper and restarted the car the buzzing/beep and brake light went away! I have recently upgraded my front calipers to an LS400 4 piston set about a month prior (full set, calipers, pads, rotors, and rca adapters) not sure that had anything to do with the failure of the previous booster/MBC. but as of now seems I have solved the problem. hopefully this thread will help anyone in the future with the same issues!