ABS troubleshooting '87
Thread Starter
6th Gear
Joined: Aug 2003
Posts: 6
Likes: 1
From: Bath ME
ABS troubleshooting '87
How do you troubleshoot ABS in an '87 without taking it to the dealer for diagnostics?
The ABS light comes on when I get up to ~5 mph and the system tries to activate. I've checked the obvious things (fuse is OK, power to the unit is OK), but from what I understand, there are no trouble code accessible for ABS in the early C4s. This leaves me with no clue where the problem lies. Is there any troubleshooting possible?
Thanx......
The ABS light comes on when I get up to ~5 mph and the system tries to activate. I've checked the obvious things (fuse is OK, power to the unit is OK), but from what I understand, there are no trouble code accessible for ABS in the early C4s. This leaves me with no clue where the problem lies. Is there any troubleshooting possible?
Thanx......
Burning Brakes
Joined: Aug 2001
Posts: 896
Likes: 1
From: Oro Valley AZ
I have been chasing the same issue on my 86 for over a month. If you have a factory manual there is a trouble shooting section and also you can check the whole system if you can find some one with the Bosh tester that plugs into the ABS main harness at the brain box. I haven't found anyone yet in AZ who can service the brakes with a tester. Good luck, and I have just been using it the way it is and haven't had any problems .
Pro
Joined: May 2005
Posts: 510
Likes: 0
From: crofton maryland
some one tol me to try cleaning all wheel sensors? mine was just pump relay went bad, my abs did nothing, i changed the relay and the light went out, but i never hear anything coming from my ABS????
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Originally Posted by actoppan
How do you troubleshoot ABS in an '87 without taking it to the dealer for diagnostics?
Thanx......
Thanx......
Here's some checks you can do at home with a Digital Multi Meter.
http://corvettefever.com/howto/19239/
http://automobiletest.com/service/1987corvette/abs.htm
http://automobiletest.com/service/19...te/sensors.htm
Last edited by 86PACER; Sep 4, 2005 at 03:57 AM.
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Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Originally Posted by L98Corvette
Not to sound like an idiot but where is the fuse for the ABS?
They are the Brake Fuse, Guages Fuse, Stop-Haz Fuse, and the INJ 1 Fuse located in the fuse panel. Which should be on the far right of the dash on the side with the passanger door open.
This is on my 86, not sure if later L98's are still the same.
Last edited by 86PACER; Sep 4, 2005 at 03:47 AM.
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
Originally Posted by actoppan
How do you troubleshoot ABS in an '87 without taking it to the dealer for diagnostics?
The ABS light comes on when I get up to ~5 mph and the system tries to activate. I've checked the obvious things (fuse is OK, power to the unit is OK), but from what I understand, there are no trouble code accessible for ABS in the early C4s. This leaves me with no clue where the problem lies. Is there any troubleshooting possible?
Thanx......
The ABS light comes on when I get up to ~5 mph and the system tries to activate. I've checked the obvious things (fuse is OK, power to the unit is OK), but from what I understand, there are no trouble code accessible for ABS in the early C4s. This leaves me with no clue where the problem lies. Is there any troubleshooting possible?
Thanx......
In your case it's most likely the signal from the ABS sensors at each wheel. The fact that the ABS light goes out after the motor starts and only comes back on once you start moving indicates that all input voltages to the ABS control module are correct and good. The ABS control module does a self check at start up, and if all input voltages from the other components in the ABS system are good, the contol module will put the ABS light out. So if the ABS light comes back on only once you reach 5 MPH it indicates a problem with the ABS wheel sensor signals going into the Control Module. I would start by looking at the ABS wheel sensors.
Last edited by 86PACER; Sep 4, 2005 at 04:03 AM.
Team Owner
Joined: Jan 2003
Posts: 20,300
Likes: 240
From: Summerland B.C. Canada
I can only offer info as i haven't had to mess with mine yet. Its from my 86 manual but should prove somewhat helpful. 
http://members.shaw.ca/agent86/ABS.pdf
http://members.shaw.ca/agent86/ABS.pdf
Thread Starter
6th Gear
Joined: Aug 2003
Posts: 6
Likes: 1
From: Bath ME
ABS troubleshooting '87
FIXED!
Thanks for the tips....turns out the right rear sensor wire was cut, apparently by road debris. Soldered it up and it's working fine. I guess it must've happened on the long drive back from Carlisle to Maine....
Thanks for the tips....turns out the right rear sensor wire was cut, apparently by road debris. Soldered it up and it's working fine. I guess it must've happened on the long drive back from Carlisle to Maine....
Instructor
Joined: Sep 2002
Posts: 137
Likes: 0
From: Toa Baja Puerto Rico
Originally Posted by actoppan
FIXED!
Thanks for the tips....turns out the right rear sensor wire was cut, apparently by road debris. Soldered it up and it's working fine. I guess it must've happened on the long drive back from Carlisle to Maine....
Thanks for the tips....turns out the right rear sensor wire was cut, apparently by road debris. Soldered it up and it's working fine. I guess it must've happened on the long drive back from Carlisle to Maine....
So, I had the unit removed from the car and had it replaced with what the mechanic called an "octopus" or distributor, where the master cylinder lines go in one side and the lines for the calipers go out the other side. A $400.00 fix
Le Mans Master
Joined: Jan 2003
Posts: 5,858
Likes: 7
From: Santa Maria CA
I wish I was that luck. The ABS compartment on mine has an old waterline errosion about 1/3 up much like an aquarium. Everything but the wiring harness is bad. All 3 relays, the Control Module (ABS computer) and the Modulator Valve itself are severly corroded internally. I pried open the relays and the Control Module and there was a huge ammount of rust in the form of dust essentially in each. I wish I had a digital camera. Looks like they were sitting in the bottom of the ocean. I think many years ago the original owner must have left the car out in the rain with the top down or someting.
I wish I had a digital camera. Looks like they were sitting in the bottom of the ocean. I think many years ago the original owner must have left the car out in the rain with the top down or someting.
Last edited by 86PACER; Sep 16, 2005 at 05:06 PM.
Instructor
Joined: Apr 2005
Posts: 128
Likes: 0
alf
Where did you get the octopus distributor?
Didn't you add a proportioning bias valve or is there one in the system somewhere
It is not in the ussual location on the frame rail so i asume it is in the anti lock motor module.
I am considering removing my anti lock system and installing all new lines and proportioning valve from an 86
but doing it behind the seat would be much easier.
Didn't you add a proportioning bias valve or is there one in the system somewhere
It is not in the ussual location on the frame rail so i asume it is in the anti lock motor module.
I am considering removing my anti lock system and installing all new lines and proportioning valve from an 86
but doing it behind the seat would be much easier.
