Hey everyone,

I think I have only one or two more problems left that I've inherited from the previous owner. The guy really did a poor job of maintaining the vehicle. (It's an 88).

Anyway, my Anti-lock Brake light comes on after I hit 3 mph, and it stays on. I've already checked my fluid level and it's fine. The moron who owned my car before allowed the front driver side caliper to be on way too lose, and it would rub against the inside of the tire during hard braking. :mad

So I fixed that, and replaced the front pads just for safe measure. Haven't looked at the rear ones yet. I know to look behind the driver side seat in the little storage compartment, and that's where the ABS "system" is. Did a visual inspection there and everything appears to be okay.

Next step I suppose is actually testing my equipment.. is there any way I can test my wheel sensors without special equipment aside from a voltmeter? Same with the computer itself.

Thanks again for your help. I've learned a tremendous amount about my car from this forum.

 

Well I was gonna say wheel speed sensors but I don't know how you test them. There should be a way to pull the codes out of the ABS system to see what it says, that might tell you exactly what's wrong.

 

I *think* I read that you can't pull the codes off an 88. 89 and up only, or something like that. I would love for someone to prove me wrong about that.. that'd make it too easy.

I also forgot to mention.. my brakes don't really seem to be as firm as they should be. Not sure if it has anything to do with the ABS problem I'm having, but I thought I'd throw it out for what it's worth. Don't get me wrong, I have no problems at all stopping. But I have an 81 Firebird that has a much firmer stop to it. It's like night and day when I decide to drive the Firebird to work.

I'll completely bleed the brakes on the Corvette to see if that helps, but I don't see it doing anything for the Antilock light.

 

The 89 module does not store codes. 90 was the first year ABS modules store codes.

Do you have the factory service manual? If not, try to get one. Trouble shooting charts are very good.

The rolling check is conducted around 4-11 miles per hour. The ususal suspects are the wheel sensors. You can check them with the ohm feature on a multimeter. The system uses the right front and left rear sensor to determine vehicle speed. As quickly as you're setting the codes, sounds like it's missing a wheel speed, maybe relays/pump. The sensor is basically a magnet with wires wrapped around, senses the tooth on the reluctor/wheel bearing assembly.

Just shooting from the hip here. For whatever reason, the RF sensor seems to cause more problems. Without jacking up the car (front), trace the wire from the sensor to the connector. Release the connector, go to ohm setting, place across pins, note reading. Should be around 900-1100 ohms. If this reading looks good, you MAY elect to remove the sensors and perform a visual inspection. You will be looking for debris, dirt, grime, grease, etc and the end of the sensor. Clean sensor. Then, take a light, inspect inside the wheel bearing, checking the reluctor, thing with teeth. Check for grease. There should be none. Wiggle the wheel bearing, check for excessive play. Worn wheel bearings can cause problems. Do not loose the little seal. You may have to do this on all four wheels. Also, check the wire routing. They are very susceptible to EMI. After you have checked all four wheels, let us know. I chased my ABS problems 3 months before finally replacing the module. Fortunately, used ones are very reasonable. New ones can cost over $1000. Wish I were kidding.

Once again, if you are planning on maintaining the car yourself, get the factory service manual. If you're unhappy with it, I'll buy it from you.

Good luck. Hope you get the thing fixed. Send Instant Message or whatever for any more questions.


dlmeyers 90 coupe zf6 3 speed shocks

 

Tourney3p0,

Here is an extensive step-by-step list of things to check for an 86-89 ABS system. I'll be submitting it as a Tech Doc one of these days.
ABS
---
Drawing on my own experience and a lot from the Aug. 1998 Corvette Fever article
by C4 Expert Gordon Killebrew there are several checks that can be done.

Static Test #1
1. 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. You will be amazed how much junk can accumulate.

2. 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.

* You can get a 10 Megohm meter for less than $20 at most any decent electronics shop. You don't need anything trick or expensive.

Dynamic Test #1
VERY IMPORTANT: Disconnect the main harness that connects directly to the ABS Controller first.

1. Set the DVOM to AC volts and you will now have to 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).

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. I personally called Gordon about adjusting the air gap and he said that it 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. You can check with Gordon at 1-800-4YOURCAR. He charges a fee of $10 + $3/minute, so be prepared to be brief or it will cost you. Gordon was a mechanic at GM who helped write the Service Manuals for the C4 vettes.

Personal note:
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 rears.


If the Static #1 and Dynamic #1 tests do not pinpoint the problem, you can do the following:

Static #2
1. 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. (Since you see the ABS light come on when shifting hard, it is VERY possible that this is your problem.)


Relays:
According to the 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 GM unit of different internal design. It is the first relay Iwould 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.

Feel free to email me directly with any questions. Please let us all know what it turns out to be that resolves the problem for you.

Good Luck,
Mike