My ABS light is on. Turns on when i turn the ignition on and stays on after running. ABS pump does not go through it;s self check. I tried diagnosing the problem using a test light and this link here:

My module relay has power on the three terminals and all grounds are good through the entire system. I used a test light and checked the high amerage single wire circuit and there was no power on it. I have not checked the pump or solenoid relay though since i did not buy a new relay to do a swap since i'm not sure if that is the problem. but having no power at the high amperage circuit doesn't sound right... but i have no clue where to go from there.

Also my guages fuse and brake fuses are good.

 

that big red wire should be hot when the key is on. check your fuse pannel, the abs gets power from a few different fuses...can't remember about the high amp on the pump,.might have a fusable link by the battery. your pump not cycling usually means A: no power B: bad pump or C: bad EBCM.

 

it's actually a big black single wire, there is no big red wires by the pump...

 

man, i just went through this with my own car a couple months ago. did you check the wiring in the FSM? also have you pulled codes out of the EBCM? this can be done easily on a 1990+ on 86-89 you need a breakout box. the service abs light being on the second the car starts means you have a hard failure. in fact it most likely comes on and stays on when the key goes to the 'on' position. i have no idea why i thought the main wire was red, it is black. i honestly can't remember if that is a ground or hot. did you verify it is 12v in your FSM? also what year is your car? just to throw it out there most abs problems on these cars are blown fuses and bad EBCMs. if the ebcm is bad the pump often does not prime because the ebcm does not send a ground to the pump. also, the ebcm failure will cause that hard code that never goes away. there is a relay on the pump with a plastic cover, bosch relay...not the metal one but the plastic one. if you pop the top off of it, plug it back in the pump, turn the key on and take a screwdriver and press the relay closed the pump should fire up. if it doesn't you have a power issue somewhere {like a fuse} or a bad pump {rare, but it can happen}

 

I don't have a pinout tester just a test light. I'm trying to figure out now how I can narrow it down and check the solenoid module, pump module, with what i have and if theyre good it could only be the ebcm i think.

This all started after i was doing valve work on the car and then had to jump start the battery after it was sitting for over a month and dead as a door nail. according to the fsm there is a red fusible link (J) which says it's near the abs harness near the jump start junction block, i assumed the block behind the battery with a handfull of other fusible links. problem is i have no clue on which one i'm looking for there. I don't see anything abnormal with any of the links there though, no burned wires and they all feel pretty solid.

Damn this has me frustrated....

 

see picture and check fuse link j for open

 

you just upped the odds of it being the EBCM. they are extremely sensitive to voltage spikes. so sensitive that i want to slap GM for not using a voltage fuse inline on them. the jump start you just spoke of is my guess. also, i know of no way to test 2 of the 3 relays easily. the one clipped to the side of the cubby is easy to test. the other 2, well you can pop the top off the plastic one and do what i mentioned above, but that is only to test the pump, not the relay. what year is your car again? i'm guessing 86-89 based on your comment about the breakout box. if so the ebcm's are dirt cheap on ebay. usually close around $25-50

 

I'd like to slap GM for giving the C4 a mind of it's own! I got in the car this morning to go to work, backed it down the driveway and whrrrrr. .... Holy SH*%T WTF? The damn car just fixed itself. I started stopped and drove the crap out of it today to try and get it to throw the light again. ...nothing. Works like it did before the problem started. I'm glad it's working now but frustrated that I have no clue why it wasn't working for days. ...Well, hopefully it won't come back and be an intermitent pain in the ***. ...wish I knew the cause.

Thanks for all the help. Hopefully it's working for good.

 

even more likely the ebcm. before mine totally quit it did the same thing. it would fire up, be fine for a few days then do the service abs light again. eventually it just died all togeather. the other thing you may have is a bad ground. the ebcm grounds by your oil filter, make sure that bolt is tight and you don't have a mass of corrosion where that group of wires bolt into the block. i'd say clean the grounds and keep driving it. if it gives you problems again; come on back with the symptoms.

 

sounds good, thanks for the help so far... hopefully i won't have to post on this problem again for a very long time.. knock on wood