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Help! 1986 ABS Light On

chris123

Well-known member
Joined
Jul 7, 2006
Messages
75
Location
Wilkes Barre, PA
Just a quick question to all those that have had experience with the Bosch ABS system, since it could save me some time and $$$; when I turn the key to the on position, I hear the relay one of the relays click about 3 times and the ABS light flashes in unison as well, then the light goes out; it will stay out until I begin to drive, and then it will stay on; I am familiar with the fact that the system is supposed perform a self-test at about 4 miles per hour, which unfortunately, the system is not doing now; before I pick up one of the Kent-Moore J35890 ABS testers on line, which I can get pretty cheap, are there any other easy checks to perform? I have the FSM, however it doesn't say you can do much other than check the "BRAKE" and "GAUGE" fuses, and make sure all the wheel speed sensors are seated properly; any suggestions to those who have gone through some testing? I'm guessing it's probably not the relays, since I can hear one clicking; hopefully it's just one of the wheel sensors, but will need the tool so I don't just start replacing unnecessary parts; actually, now that I'm mentioning it, does anyone have the AC Delco parts #'s for both the pump motor and solenoid relays that sit on top of the modulator valve? If they are fairly cheap, I may start with those 2, since even though I can hear one of them clicking, not sure if the other is working as well.......


Regards, Chris
smile5.gif
 
You might try to get up to 60 or 70 and jump into the brakes hard enough to get them to activate. Believe me it takes a lot of effort to get the abs to work but the shaking and pulsing of all the sensors may brake lose a stuck sensor. Bring the car to a complete stop and then do it again. Be safe and pick a good clean road that you can tell there is not other cars near you.
 
Troubleshooting

Just a quick question to all those that have had experience with the Bosch ABS system, since it could save me some time and $$$; when I turn the key to the on position, I hear the relay one of the relays click about 3 times and the ABS light flashes in unison as well, then the light goes out; it will stay out until I begin to drive, and then it will stay on; I am familiar with the fact that the system is supposed perform a self-test at about 4 miles per hour, which unfortunately, the system is not doing now; before I pick up one of the Kent-Moore J35890 ABS testers on line, which I can get pretty cheap, are there any other easy checks to perform? I have the FSM, however it doesn't say you can do much other than check the "BRAKE" and "GAUGE" fuses, and make sure all the wheel speed sensors are seated properly; any suggestions to those who have gone through some testing? I'm guessing it's probably not the relays, since I can hear one clicking; hopefully it's just one of the wheel sensors, but will need the tool so I don't just start replacing unnecessary parts; actually, now that I'm mentioning it, does anyone have the AC Delco parts #'s for both the pump motor and solenoid relays that sit on top of the modulator valve? If they are fairly cheap, I may start with those 2, since even though I can hear one of them clicking, not sure if the other is working as well.......


Regards, Chris
smile5.gif

I'm most familiar with the system on my '89, but assume it's basically the same. There is a decent amount of diagnostic stuff in my FSM not pertaining to the factory ABS testing tool. Runs through the typical troubleshooting of specific components in the system, lists sensor specs to test against and wire colors for each individual sensor, describes the "sequence of operation" for the system, etc. Maybe your earlier manual doesn't have that same info. Also, I believe someone posted a link, perhaps last summer - it had some tips for doing ABS troubleshooting without the factory diagnostic tool, ran through a process for checking the relays, etc. Maybe that might show up in a search or perhaps someone else remembers it. I probably printed copies, if I can find them. Anyway, I was able to diagnose my own system using only a DMM using the information in the FSM and the extra information I mentioned. It took me a while to run through all the tests listed, as there are circuits in a number of places that need to be checked and of course none of it is easy to get at. Ultimately everything tested out "ok" and my actual control module was the culprit. To your own situation, am I understanding that the lamp goes out once the vehicle starts and stays out until you drive? Once you start to move, the control module looks for signals from the wheel sensors. If it doesn't see those signals, the light comes back on. So, a wheel sensor would be my first guess. Depending on what you're most comfortable doing first, both mechanical inspection and electrical testing would be appropriate to see if the sensors are at least in place and intact electrically.
 
You might try to get up to 60 or 70 and jump into the brakes hard enough to get them to activate. Believe me it takes a lot of effort to get the abs to work but the shaking and pulsing of all the sensors may brake lose a stuck sensor. Bring the car to a complete stop and then do it again. Be safe and pick a good clean road that you can tell there is not other cars near you.

John: Thanks, I will take a quick look and see of all the sensors appear to be intact and seated correctly before I do the lock-up test.....

I'm most familiar with the system on my '89, but assume it's basically the same. There is a decent amount of diagnostic stuff in my FSM not pertaining to the factory ABS testing tool. Runs through the typical troubleshooting of specific components in the system, lists sensor specs to test against and wire colors for each individual sensor, describes the "sequence of operation" for the system, etc. Maybe your earlier manual doesn't have that same info. Also, I believe someone posted a link, perhaps last summer - it had some tips for doing ABS troubleshooting without the factory diagnostic tool, ran through a process for checking the relays, etc. Maybe that might show up in a search or perhaps someone else remembers it. I probably printed copies, if I can find them. Anyway, I was able to diagnose my own system using only a DMM using the information in the FSM and the extra information I mentioned. It took me a while to run through all the tests listed, as there are circuits in a number of places that need to be checked and of course none of it is easy to get at. Ultimately everything tested out "ok" and my actual control module was the culprit. To your own situation, am I understanding that the lamp goes out once the vehicle starts and stays out until you drive? Once you start to move, the control module looks for signals from the wheel sensors. If it doesn't see those signals, the light comes back on. So, a wheel sensor would be my first guess. Depending on what you're most comfortable doing first, both mechanical inspection and electrical testing would be appropriate to see if the sensors are at least in place and intact electrically.

89: Thanks for the info; yes, the light will stay out until the wheels actually start moving; I will double check each sensor to see if anything is obviously out of whack; I know that the left front sensor connector was repaired by the previous owner, so I may wind up checking that one first; will keep you posted on the results.......
 
Those Bosch relays are not unique to early C4s. They are available from many sources.
 
I run on to this problem all the time!
I usually find a rear wheel sensor relucter ring on the half shaft covered with metal filings from the brakes or a chewed up sensor tip from a loose WB!
 
I run on to this problem all the time!
I usually find a rear wheel sensor relucter ring on the half shaft covered with metal filings from the brakes or a chewed up sensor tip from a loose WB!


Junk: The system is not even performing the self-test at the 4 mph point, so I know the first set of checks is to check that relay, however I will definately check those rear sensors as well...........


Those Bosch relays are not unique to early C4s. They are available from many sources.

Hib: Thanks; I did a couple of searches so far and came up empty; do you know of any sources to purchase from other than a used one from a recycler?
 
Relays and misc.

Junk: The system is not even performing the self-test at the 4 mph point, so I know the first set of checks is to check that relay, however I will definately check those rear sensors as well...........




Hib: Thanks; I did a couple of searches so far and came up empty; do you know of any sources to purchase from other than a used one from a recycler?

The link Hib posted contained the "extra" information I referred to earlier. I hoped someone else would come up with it. With the relays, try searching some of the national auto parts chains (whatever is local to you). I don't recall having too much trouble locating them when I was doing my own searching. Automotive relays like those used are quite standardized and they can be used for many applications. The same type relay used in the Corvette ABS system may be used to operate foglamps on a different make/model vehicle....
 
At RockAuto.com
1986 CHEVROLET CORVETTE 5.7L 350cid V8 : Electrical-Switch & Relay : ABS Relay Price
STANDARD MOTOR PRODUCTS Part # RY304 {Click Info Link for Alternate/OEM Part Numbers} A/C CONTROL RELAY; Terminal Type Stud Terminal Gender Male Direct OE Replacement 12 Volt Number of Terminals 4 Mounting Bracket No Continuous Duty No Contents Relay
4 Term.

RockAuto.com is a CAC sponsor.

Also, you could pull out the relay, take to a GM dealer and ask if they have a replacement.

Good luck.
 
Also, you could pull out the relay, take to a GM dealer and ask if they have a replacement.
Most GM dealers will have them,there used on almost every GM vehicle since about 1982 till 1997-98 somewhere in the electronics,(Fords Too!) Even the later model relays that plug into the power distribution center will plug in and work with no ill effects in a pinch,You'll just have to use a zip tie to mount them!:thumb
 
At RockAuto.com
1986 CHEVROLET CORVETTE 5.7L 350cid V8 : Electrical-Switch & Relay : ABS Relay
Price
STANDARD MOTOR PRODUCTS Part # RY304 {Click Info Link for Alternate/OEM Part Numbers} A/C CONTROL RELAY; Terminal Type Stud Terminal Gender Male Direct OE Replacement 12 Volt Number of Terminals 4 Mounting Bracket No Continuous Duty No Contents Relay
4 Term.

RockAuto.com is a CAC sponsor.

Also, you could pull out the relay, take to a GM dealer and ask if they have a replacement.

Good luck.

Hib: Thanks for the link; will order from them if necessary; they offer a 5% discount to forum memebers, but the guy I spoke with said to check with one of this forum admin's for the specific discount code to use when ordering on line? Also, it looks like there are 3 realys in total, the pump motor and solenoid relays are the ones in the link above, however do you know of any source for the module relay? I think it is part #: 1636973. I had no luck with my searches in trying to find one of these relays......
 

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