Rear antilock and Brake light on

[jar2187]

Well my rear antilock and brake light have been on since I bought the truck. The brake pedal is very spongey, I have replaced the master cylinder and the light is still on. Replaced the front brakes the other day and the brake light shut off for 2 days and then came back on, rear antilock light was still on at the time. If you unplug the connector that goes to the master cylinder the brake light shuts off.. When you plug it back in it turns back on. When you ground out the abs connector under the dash, the abs light flashes 4 times. I have posted this problem a few months ago and was asked if I could unplug the abs computer behind the dash. Well at the time I couldnt. Untill the other day, I unpluged it and the Brake light and the Rear Antilock light went out. If you plug it back in they both turn back on. With it unpluged I checked to see if the brake light still worked, put the ebrake on light didnt come on, then pushed the float down in the master cylinder and the light came on, So i left the computer unpluged.
My question is, How come the lights turn off with the abs computer unpluged. Not getting signal that the rear proportioning value it bad. I remember someone saying if the lights turn off when the computer is unpluged it the computer. So which is it the computer or the rear proportioning value?

 

[Rhett]

I'd say its the computer. You are right, you would think the ABS light would be programmed to come on if the system is disconnected, after all that would be a failure in the ABS system.

You say your brake pedal is spongy. If it's still spongy then you need to bleed the whole system, and that includes the ABS. You would think that when the master cylinder was replaced that all the air would have been bled out then, but sometimes it's tough getting it all out, and ya don't want air bubbles especially in the master cylinder. Bleeding the ABS is tricky and most people recommend a dealer do it; apparently it seems that the dealerships have some sort of expensive machine that makes it easy to bleed the ABS.

 

[jar2187]

I just have rear abs and it doesnt need a speical tool to do bleed them. Maybe they Werent bleed right, my dad thought they were bleed enough when we changed the master cylinder