Guys(and gals), while working on my 91 vert I found that Buba had pulled out the "Service ABS" bulb out of the DIC so I couldnt tell that there was a problem. I put in a new bulb to find that it stays on whenever the car is on. The pump does not appear to energize right after start up like the manual says it should. I am not getting any codes whatsoever and let a mechanic hook it up to a diagnostic machine to see if he can pull the codes. His machine said the same thing. Where do I start? Should I just take it to a specialist? Any help would be appreciated.

 

Sounds like you have some sort of electrical short or ground problem or the Electronic Brake Control Module has gone south.

There are a number of tests that a service tech can make to determine whats wrong. A Tech 1 with the brake cartridge will be needed to find the problem.

Of course, your ABS is not working and there is also a possibility that the airbag may not work depending on the type of ABS problem, so drive carefully to the shop! You may need to bring money...lots of money.

 

On the 90, you hear the ABS pump cycle up when you reach 3 mph. I agree, if you are not hearing anything at all, that probably the controller went south. Wierd though, the Service Light comes on but you can not retreive any codes. Whose the "Bubba" that removed the bulb? Any chance that he has some "histroy" about this? If you bought the Vette from a dealer, you should be able to hold their feet to to the fire so to speak. my ABS has saved my butt a couple of times on icy roads, definately I would not want to drive without it.

 

I bought the car from out of state from an individual, so chances are I wont find out what is wrong or has been done to it. Fortunatly, the 91 is an extra vehicle and I dont drive it everyday. I think I might see if someone around here knows of someone that specializes in ABS work. Thanks

 

The fact that you can't hear it cycle at all is interesting. My ABS light comes on as well, so I checked the wheel sensors. One of my sensors was physically broken so I ordered a replacement from Jeff Kopp for a very good price. I'm hoping when I replace the sensor it'll clear up the problem, but I also don't hear or feel anything at all when it's supposed to do the cycle.

 

Tourney3p0, keep me posted on what happens with yours please. Thanks, Scott

 

RETRIEVING CODES USING ANTI-LOCK LIGHT
Flash Code Method
1) With ignition off, install jumper wire between pin "H"
(White/Tan wire) and pin "A" (Black/White wire) of Assembly Line Data
Link (ALDL) connector. The ALDL connector is located below left side
of instrument panel, near steering column.
2) Turn ignition on. Diagnostic display mode will remain
active as long as pin "H" is grounded, serial data link communications
has not been initiated, and vehicle speed is less than 4 MPH.
3) Approximately 3 seconds after ALDL pin "H" is grounded,
EBCM will begin flashing SERVICE ABS light to indicate trouble codes
in sequence. Sequence will start with Code 12 to signal the beginning
of trouble code display.
4) Each stored trouble code will be displayed 3 times. After
all trouble codes are displayed, sequence will be repeated.
NOTE: Codes 41, 45, 55, 61 and 63 can ONLY be read through ALDL
using TECH 1 if trouble code is currently present (current
code). The EBCM will not allow any trouble codes to be
flashed if any of these codes is current. If trouble code
existed previously (history code), but is not currently
present, trouble code can be read using SERVICE ABS light.

Maybe you are not getting anything because the codes are current and your not useing a TECH 1? If you need more info just post here and I'll send you some more tests.

Good Luck.

 

Search the archives. I've posted more deatiled instructions on possible ABS problem testing before. At a minimum you should chek all 4 wheel sensors. They attach to the wheel knuckles with one screw. Unscrew each one and check the end for dirt. The sensors are powerfull magnets and attract a lot of metallic dirt over time. Too much road debris will throw off the readings and cause the ABS controller to see a fault at startup. That causes it to not test the system and to turn on the ABS light. The sensor ends can be safely cleaned with WD40. The fronts can be done easily with the tires on the car. So can the rears, but it is a good bit easier to get to the rear sensors if you remove the rear wheels.

Since the ABS system doesn't even appear to run the pump test at startup it is likely that one of the 3 relays is bad. Ideally you have them tested by a shop that has a relay tester. You could try replacing them one at a time to see if that solves the problem. All 3 from Jeff Koop will run you just about $100, but that is probably chgeaper than the dealer will charge just to run the tests. All 3 relays are in the compartment behind the driver seat. It's trickier to get in there on a vert more so than on a coupe, but they are there and can be replaced without going to the dealer.

Relays:
According to my GM Parts & Illustartion Guide the 1986-1991 C4 ABS system has 3 relays. The GM Part #s are:
14105967 ... RELAY, PRESS MOD VLV SOLENOID
14105968 ... RELAY, PRESS MOD VLV PUMP MTR => Replaced with GM part # 12513302
1636973 .... RELAY, ELEK CONT

The 14105968 relay was replaced with a later GM unit of different internal design. It is the first relay I would replace and then follow that with a new 1636973 unit. Forum member Jeff Koop 800-728-8267 can get all 3 for you at a major discount to the usual GM dealer price. Approx $35 each from Jeff, $54 each from dealer.

Let us know how it goes.

Good Luck,
Mike

 

Replaced the wheel sensor and my antilock light is gone. I still don't hear it cycle, but then again my exhaust is very loud.

 

With this system, get your hands on a factory service manual. A great help with this system, even with no codes stored.

With your symptoms, checked my 90's service manual, (not same but very similar) and the trouble shooting started with verifying power. There are fuses and fuseable links associated with system operation. It must have power to work. Then, after power verification, it's off to the relays. Good post above on relays. For my money, it's check power and relays. Have seen complete modules, pumps, and relays for under $100 on ebay. Spent $160 for my 90's module, pump, and relays. At any rate, with a service manual, you will gain more confidence with what you're doing.

Let us know.

dlmeyers 90 coupe zf6 3 speed shocks