scorp508

Ever since putting the new rims on my car I've been getting this. I'm hoping it is just coincidental as both front and rear rim/tire combos have the same overall height.

My car will do the 3mph self test and be good to go. After a few initials stops or applications of the brake pedals the ABS light comes on, stays on, and the car reverts back to non-ABS mode until you turn the car off and on again.

If I slam on the brakes hard enough the tires lock up and a sliding we shall go through whatever hard object comes in front of us. It really isn't an issue because the car stops fine before having to brake so hard things lock up, but still it sucks to have a light on.

Now, my question to all of you is if you know HOW I can get whatever code is set for the ABS light being on. The version of EASE I have doesn't provide ABS stuff, the MT2500 Snap-On scanner cartridge I've currently got has no ABS tests (I guess I should ask dad if he knows of one that works), and as far as I know back in the 80s there was a standalone ABS test computer that GM dealerships used to find this stuff out. I've never seen it since that means I was 7 years old then. :lol:

Anybody know for sure? I don't feel like replacing all 4 wheel sensors blindly just to find out later its the $600 ABS pump.

rick lambert

Yeah, the tester is J35890 ABS tester-don't know where you can get one-maybe dealer. But since it only began after new rims and tires, I suspect one or more of the wheel speed sensors got messed with. I'd check them first. Then check to see if the control module connector is securely connected and the ABS connectors, brake fuse and guage fuse. Good luck and please let us know. ;)

jfb

No error codes are stored for the ABS in 87. Find a dealer that still has an ABS tester, thats how I found my defective LR wheel sensor and I looked at the waveform of all four sensors with an oscilloscope and couldn't see any difference between them.

tequilaboy

Most likely a sensor signal, or bad/intermittent connection. If your getting past the pump self test ok, this means the all the electrical connections are intact for the pump motor, pump motor relay, wheel speed sensors and solenoid valves. If a fault is detected while driving it is most likely an implausible sensor signal (frequency too high or noisy, etc.) or an intermittent open circuit somewhere in the harness or at one of the connectors. I had a similar problem with my 88 that was "cured" by unplugging and re seating all the relays and connectors on the ABS module.

I also have some 86-89 trouble shooting info from some friends at Bosch with wiring diagrams and pin-out resistance values that I can e-mail, (if I still have it on my work pc. will check tomorrow.)

scorp508

Thanks everyone. I guess I'll be starting with reseating everything and maybe I'll clean the wheel sensors off one more time.

Hawaii89vette

HI Tequilaboy,

I would appreciate a copy of the ABS troubleshooting guide. Currently my ABS light on my 89 Coupe is always on.

Thanks
-Tim (timleedude@hotmail.com)

Wheelman

:withstupid:
Could you send me this info too please? dkredmetallicc4@hotmail.com

XtremeVette

hey brian!!!! whatup Mr. ScorpMan.....I see you got the yellow beastie running once again...man I haven't talked to you in a long while here.....

to maybe help you out.....do you have a manual of any kind on that 87 of yours....Iam not 100 percent on how your system works but if you are throwing a light then I believe your computer will indeed store the code.....in my manual if I jump and ground certain pins on my ALDL connector under the dash....the car goes into ABS diagnostic mode and will blink the ABS light the same way the service engine light works when in diagnostic mode.....I already tested it out on mine....i bring up a code 45....front wheel sensor missing....Iam doijng this through my lil code scanner which has a switch on it....ABS or ENGINE...bought it down at autozone or you can get it at advance auto for like $30. its made by ACTRON ...says GM code scanner for OBD 1 cars......but like I said all this scanner does is the same thing you could do with a jumper and 2 pins......I would tell you what pins to jump....but more then likely your 87 might be different then my 90.....so check out your manual....this info might even be in your owners manual to the car.....

well let me know how it goes ok....
ttyl
jeff

Davemc1963-87conv

[QUOTE]HI Tequilaboy,

I would appreciate a copy of the ABS troubleshooting guide. Currently my ABS light on my 89 Coupe is always on.

If you're feeling charitable, would you also send it to me please, my 87 has had it's light on for years and I have been unable to track down the fault. please take out the four spaces in my e-mail address.
TIA
dave mc1963 @ hotmail. com :cheers:

dlmeyers

Couple of points.

The MT 2500 scanner will work with MY90 and above. You can menu around and watch all four wheel speeds at once, MY90 and above. It's best to have someone else drive while you watch the scanner. I love watching the numbers. As correctly stated above, 86-89 ABS systems would not interface with scanners. The filing cabinet size special test set is getting harder to find. When you find one, they may or may not have anyone who knows how to use it. Have seen them on ebay.

I would first check the brake fluid level. Then, remove and clean all sensors. With sensors out, use a light and check the reluctor mounted in the wheel bearing housing. Check for general condition, clean teeth, etc.

With all that done, we have to look at the tire rim variable. The ABS computer is calibrated to a particular tire size/rim. The right front sensor and left rear sensor speed signals are used to calculate vehicle speed. If all tire/rim sizes changes are proportional, I don't see how that can be a problem.

For the 86-89 cars, there's a good post about 2 years old that used some test proceedures using a good DVOM checking each wheel circuit. I'd search under ABS and see what happens.

Good luck and let us know.

JackDidley

Hey Scorp, how old are your wheel bearings? If the bearings get sloppy the ABS sensor gap goes out of spec. You geta ABS light. This happened on my 86 and my old ladys' 94 Camaro. Worth looking at. :chevy

scorp508

Excellent point! I totally forgot about this possibility. I know for a fact that my right/front bearing has some play in it and I just haven't gotten to replace it yet. I remember now my light coming on when my rear bearings had play in them. Looks like I have to replace that before anything else. :cheers:

tequilaboy

I'll be happy to provide the info that I have. Note: I have found the hard-copies, but have not yet found the electronic copies, but I have more archived e-mails to check through. I'll look a little deeper tomorrow, or worst case I can scan what I do have and send along.

Jloshotz

:withstupid: :withstupid: :withstupid:

87NassauBlue

Hey this wouod be great info to post here. I have and 87 with problem too.!! :smash:

Mike_88Z51

Scorp,
As already mentioned the 86-89 ABS systems DO NOT interface with the ECM and do not set codes like the 90+ Vettes. Ours use a simple Fault/NoFault condition to decide if the ABS is to stay active or not. Since your system passes the initial low speed check, the sensors are probably good and the fault is most likely the bad front wheel bearing you mention or the change in rim size you made. I actually bought the official GM Kent-Moore ABS test unit for my 88 ABS and have done a LOT of research in this area. (The test unit is not file cabinet size, but it is'nt laptop size either. )

I need to put this in the Tech Tips once I get some pics to go along with it. This is a copy of a post I made a good while back that might be of help to several members with pre-90 ABS.

First : Pull each sensor and clean with WD40. The sensors are essentially powerful magnets and they will accumulate a lot of road dust and debris which affects the sensor readings. The sensors are screwed into each wheel knuckle with a 10mm screw. After you clean them, use a little anti-seize on the sides to keep the steel sensor from welding itself to the aluminum knuckle. See if that helps.

Static Test #1
Using a digital volt/ohm meter (DVOM) with a 10 megohm reisitance, disconnect and check the resistance across the 2 pins on each of the wheel sensors. They should read 900 to 1100 Ohms. They should also all be within 100 ohms of each other. If not in range, clean with WD40. If still not in range, replace the sensor. You can pull the sensor connector where it connects to the main wire for each sensor going into the main harness, or you can disconnect the 8 pin connector in the ABS compartment on the drivers side under the plastic tray. If you use the connector behind the seat you need to get the correct pair of wires for each sensor. Check the ABS wiring diagram for you year car in the manual. For my 88 the wire colors are:
LF - yellow & blue/white stripe, RF - Green/white & brown/white,
LR - red & black, RR - brown & white.

Static Test #2
Check your laterial acceleration switch, remove the right console carpet and locate the switch behind the AC/blower controls (it will have a orange and orange/black wire). Test it by holding it in your hand in the same position as it was mounted in the car and measuring the resistance with an ohmmeter. It should read zero ohms.

Then turn it 90 degrees to vertical and check for an open (or infinite reading). If it fails this test replace it. Check the junk yard for one. Nobody usually buys them there because they seldom go bad. So you should be able to get one for about $20.

Dynamic Test #1
VERY IMPORTANT: Disconnect the main harness that connects directly to the ABS Controller first.
Note: this test is essentially the same as what the Kent-Moore J35890 ABS test tool tests in the ABS controller, we aren't testing the relays at the same time like the K-M ABS Test tool does.

Set the DVOM to AC volts and go to the ABS 8-pin connector in the ABS compartment on the drivers side under the plastic tray (unless you have or can borrow a Kent-Moore J35592 Pinout Box). Again, for my 88 the wire colors are:
LF - yellow & blue/white stripe, RF - Green/white & brown/white,
LR - red & black, RR - brown & white.

You will need someone to make AC voltage readings for each wheel sensor while you drive at 15 MPH. The left front should read .65 millivolts and the right front close to the same. The rear sensors should each read 1.1 millivolts. If your reading is high it means the air gap at the toothed gear is too small. A lower reading would mean too much of a gap. If the air gap does not match left to right it could be caused by worn wheel bearings. If the air gap is out of adjustment it will cause the ABS light to come on. The air gap is not really adjustable. To decrease the gap you may need to sand the area where the sensor attaches to the wheel knuckle.

To increase the gap you need to put a layer of paper between the sensor and the knuckle. A meer fraction of an inch makes for a major change so DON'T do this unless you are sure it is not due to a loose or bad wheel bearing.

I have found that the front wheel bearings have a minor amount of play in the way that they mount to the car. Once they are bolted in, they are in solid, but they can be mounted a tiny bit more forward or aft of center. Since the toothed wheel that induces the voltage to the ABS front sensors are on the front wheel bearings, this will allow you to make a minor adjustment in voltage if your reading is slightly too high or too low compared to the other front sensor, by adjusting the wheel bearing. This doesn't work for the rear. A bad wheel bearing can cause the voltage to be off enough to set the ABS light. That was the cause in my case.

Another point of failure is one of the 3 ABS relays. According to my GM Parts & Illustartion Guide the 1986-1989
C4 ABS system all use the same 3 relays. The GM Part #s are:
1636973 .... RELAY, ELEK CONT
14105967 ... RELAY, PRESS MOD VLV SOLENOID
14105968 ... RELAY, PRESS MOD VLV PUMP MTR => Replaced with GM part # 12513302

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

Mike

vinnies87

Could also use a copy.... thanks vincedaddio@***.net