Need help please ABS INOP
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Need help please ABS INOP Hey everyone not new to the site just lost my old log in credentials. Need some help asap. I have my abs inop and BRAKE lights on. Iv read and read and read countless of threads on the abs fault. My MC was leaking so i replaced that, bled the brakes with complete new fluid and it is still on. Today i was diagnosing my abs problem further when i made a discovery if i turn my car on (95 z28 auto) with the brake pedal pressed all the way to the floor it turns on with no lights. As soon as i let go my lights dim and i hear what im assuming is the abs pump turn on and the lights turn on. My question is i know its not a connection or the ebcm do you all think it could be the abs pump? My MC is new with new fluid
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Hey all thanks for the replies, well my pedal doesnt go all the way down it needs maybe a half of an inch more to reach the bottom. Also i followed a write up on how to bleed the brakes which states i have to bleed the rear abs nipple first then the front then the regular bleeding precedure stsrting with the farthest wheel to the closest to the mc then bleed the front abs nipple then the rear, cylce the abs pump and then re bleed the whole system again.. I did it yesterday and still nothing what i noticed was it actually has jothing to do with the pressure it is jn fact the brake switch. I removed the switch left the pedal alone and everytime i start the car with the switch on( thinking the brake is applied but it its not) the abs is off as soon as i press the button(thinking the pedal is up) the abs turns on?? I dont think it is the switch as they are just contacts and it would either stay on or stay off. Does any circuit pass throught the brake light switch?
Staging Lane
Joined: Nov 2014
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From: North Carolina.
Try going a slow speed somewhere safe, perhaps the road you live on and just slam
the brakes going about 15-20mph, make sure no one is behind you! It sounds silly and unorthodox however, it got rid of my brake light...As for the ABS INOP, mine has done this twice, one time because my third brake light was out (you should check that if you haven't) and the second time was after doing a brake pad swap in the rear, I took the negative battery cable off for 10 minutes, put it back on, the light hasn't been back on since. Hope this helps!
the brakes going about 15-20mph, make sure no one is behind you! It sounds silly and unorthodox however, it got rid of my brake light...As for the ABS INOP, mine has done this twice, one time because my third brake light was out (you should check that if you haven't) and the second time was after doing a brake pad swap in the rear, I took the negative battery cable off for 10 minutes, put it back on, the light hasn't been back on since. Hope this helps!
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There is air in the system still or you have a leak. There should be very little action in the brake to fully engage them. I'm telling you that Motive bleeder will make bleeding your brakes so much easier.
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From: Nebraska
Rightfully you need a Tech II or the like to activate the solenoids in the ABS unit to bleed air. Or like said, you can go find a gravel road and stomp on the brakes to activate the ABS. Although the ABS has to work for it to do that.
You don't absolutely need a Tech 2. As long as the ABS has not activated since you bled down the brakes, the modulators will be in their home positions and you can bleed the ABS unit using the two external bleed nipples.
I agree with SS RRR, it sounds like you still have air in the system.
I agree with SS RRR, it sounds like you still have air in the system.
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I bled the brakes going on my fourth time if i do it again. And what i found out is my abs only activates when the brake switch is pressed inif i start the car with the pedal up but the button depressed the abs will not trigger. Im waiting on the aldl 16 pin obd1 cable to arrive so i can scan it with the scan9495 program that was offered to me by GaryDoug. Might be a week also im not sure its a leak i ran through my whole brake system and dont seem ti find a leak. What should i look for when im scanning my abs? What code will pop up if there is in fact still air in my system? And will i be able to bleed my system with that program?
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Also abs has been on in the vehicle since the first day I got it. Also the master cylinder had been leaking ever since too. My brakes work fine and stop great the thig is that the lights never turned off.?.
TECH Resident
Joined: Jun 2013
Posts: 853
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From: Kernersville, NC
Even with the above(Motive bleeder), I had a slightly soft pedal. I was finally able to solve that problem(by cycling the abs motors several times and bleeding the ABS modulator) when I bought a Tech 1(yes... a Tech 1) off ebay with the correct mass storage cartridges and OBDII adapters.
I didn't ever get an ABS INOP light through that entire process.
For the "brake" light, check your ebrake switch at the console handle(detects if the handle is up or down)....as well as the level being low in the brake master cylinder reservoir. It also could mean a problem with the brake system according to the drivers manual.
Given your ABS INOP light, I suspect the brake light on is a result of whatever is wrong ABS system.
Given that so much has been done to the car and that issue has been there since you bought the car, I think you need to pull the codes for the ABS system to see what the car is flagging as a problem.
To my knowledge, you will need a Tech 1 or 2 tool to do this as the ABS bus resides on a different bus than the PCM/ECM(that is why general code scanners can't pull ABS codes...at least on OBDII cars).
I'm not sure on OBDI cars....I do remember reading that Gary may have a solution to pull ABS codes. It should help in trying to isolate the issue. Could be a bad ABS motor pack, isolation solenoid, wheel speed sensor(that has turned on my ABS INOP light before....had to get new front hub...just replaced both since they were almost 20 years old...wow, that seems so wrong....20 years....), etc.
Last edited by ACE1252; Jan 17, 2015 at 06:07 AM.
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Ok well today i got my cable in i downloaded the software and im getting a no response by pcm message?. My car starts fine i also got data masters to check if it might be the software and when i pressed on test a message came up and said aldl cabke working fine. And something about the data not being able to be read, it suggested to try another software? I checked my pcm and its the correct one for the year. Im really stumped at this point i just want to junk the damn car already. Any suggestions?
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Ok well i fanally gotnit to read, i had to switch from the ground on pin 5 to pin 4 not sure whats going on with that, now i have abs codes 45 46 and 86 . 86 is just the lights being on due to 45 46 they are as follows
DTC 45 Right Front ABS Channel Does Not Move
DTC 46 Rear ABS Channel Does Not Move
DTC 45 Right Front ABS Channel Does Not Move
DTC 46 Rear ABS Channel Does Not Move
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Would anyone happen to know what they mean? I tried searching cant seem to find a legitamate answer some say its the abs module others say its the sensors in the tire and diff?
Last edited by 95z28ltt1; Jan 21, 2015 at 05:29 PM.
TECH Resident
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From: Kernersville, NC
EDIT: this is wrong....see my next post....
It could be either the sensors or the input receiving them....
The sensors need to be tested for output. On a tech 1 or 2 tool, when driving, you can view individual wheel speed to see if there is any kind of output from the sensors at all being received.
I'll do a little digging to see if GM suggests another way to test the sensors other than with a tech 1 or 2.
It could be either the sensors or the input receiving them....
The sensors need to be tested for output. On a tech 1 or 2 tool, when driving, you can view individual wheel speed to see if there is any kind of output from the sensors at all being received.
I'll do a little digging to see if GM suggests another way to test the sensors other than with a tech 1 or 2.
Last edited by ACE1252; Jan 21, 2015 at 09:19 PM.
TECH Resident
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From: Kernersville, NC
Ok, I just looked up the codes and they are not referring to the wheel speed sensors at all....glad I looked them up.
Both ABS codes 45 and 46 are referring to the ABS modulator/motor pack.
There are 3 motors on the ABS modulator, a left front, right front, and one combined for the rears. For some reason, when your right front and rear motors are commanded to go to home on start up, they are not moving(locked up).
This could point to a bad ABS motor pack, seized pistons in the ABS modulator, power or short issues to the wiring of the motor packs.
The EBCM is looking for current feedback from the motors to determine if they are doing the proper movements.
Most of the diagnostics in the GM manual are using a Tech 1 or 2 for the troubleshooting process. Commanding the motors to home, move, etc. It will also tell you the current draw from each motor(I've seen this myself when cycling the motors to purge the ABS modulator of air with my Tech 1).
Here are a couple of iphone photos from my '96 factory manual. Just be aware, that wire numbers and/or colors may be different from another model year. The pictures are big, but I left them that way to zoom in on the text, even though it is a little blurry.
http://www.ace1252.com/1996_Z28_Fact.../ABS_DTC45.JPG
http://www.ace1252.com/1996_Z28_Fact.../ABS_DTC46.JPG
Both ABS codes 45 and 46 are referring to the ABS modulator/motor pack.
There are 3 motors on the ABS modulator, a left front, right front, and one combined for the rears. For some reason, when your right front and rear motors are commanded to go to home on start up, they are not moving(locked up).
This could point to a bad ABS motor pack, seized pistons in the ABS modulator, power or short issues to the wiring of the motor packs.
The EBCM is looking for current feedback from the motors to determine if they are doing the proper movements.
Most of the diagnostics in the GM manual are using a Tech 1 or 2 for the troubleshooting process. Commanding the motors to home, move, etc. It will also tell you the current draw from each motor(I've seen this myself when cycling the motors to purge the ABS modulator of air with my Tech 1).
Here are a couple of iphone photos from my '96 factory manual. Just be aware, that wire numbers and/or colors may be different from another model year. The pictures are big, but I left them that way to zoom in on the text, even though it is a little blurry.
http://www.ace1252.com/1996_Z28_Fact.../ABS_DTC45.JPG
http://www.ace1252.com/1996_Z28_Fact.../ABS_DTC46.JPG
Last edited by ACE1252; Jan 21, 2015 at 09:57 PM.