I'm about toe begin, again, trying to track down the casue of my ANTI-LOCK dash light.

Haven't found anyone to help me with the voltage tests while driving yet. I should be able to corral my son for this duty over the weekend.

I noticed in the compartment behind the driver's seat where the ABS is installed there is a two wire connector with a resistor soldered in.

The wires and green and white and are not plugged into anything. There's simply a resistor soldered between the two terminals and the wires are just laying loose.

There's nothing for them to plug into and, in fact, they couldn't plug into anything with the resistor in the way.

It's obvious this isn't a factory arrangement. Does anyone know what these two wires could be for and, possibly explain the need to add a resistor to them? Apparently the previous owner had ABS problems before too.

Thanks,

Jake

 

Hi.

I can`t say whether or not it should be like this from the factory but my 86 also has the resistor in the end of that connector as well.....

Hope u manage to finally track the problem down. I don`t care whether a car has ABS or not - but i like everything to be working like it should.

Good Luck,

Dom

 

The resistor is actually factory. Go figure. I didnt read completely thru the post again but have you pulled all the sensors? Mine turned out to be a bad rear wheel sensor. I replaced it and it was fixed. Where is Desoto? If you are remotely near Austin, I have an extra ABS computer, pump, relays, 2 front sensors, and right rear sensor you can use to test your system. I also have the Wagner service manual you can borrow if you need it. LMK

 

Wow, that's really surprising. I never would have figured the factory would rig something like that and just leave the wires and connectors hanging loose inside the compartment.

DeSoto is right outside Dallas, so I'm a pretty good ride from you. Thanks for the offer though

Today, I pulled off the wheels and checked the sensors AGAIN. They were all clean. According to the instructions another member sent me, in order to check the wires and sensors for the wheels, the car would need to be in motion and the readings taken while it's moving.

I bled the brakes, flushing out all the old fluid just to have that base covered. I then checked all the brake pads (plenty of meat left) and the torque on the rear nuts. Did the old shaker-roo to check the wheel bearings and they're okay.

An aside: never noticed before that with the rear wheels off the ground AND the trans in neutral with the engine idling, the rear wheels still turn. I guess neutral doesn't REALLY mean neutral.

Then I tracked down an old copy of Vette magazine (or was it Corvette Fever) and found the article on trouble-shooting the ABS with a test light.

I couldn't get it to light on pin 9 for the module relay; BUT THE LAST TIME I CHECKED IT - ABOUT SIX MONTHS AGO WHEN THIS ALL STARTED - I got voltage there. I remember trying a different module relay - it's the silver colored one - that was sent to me by another Forum member and even with his I got voltage. Now no voltage; what gives??!!

According to the mag article, I should be able to disconnect the big connector, turn the ignition key to "ON" and get voltage at pin 9. If voltage is there, then the relay is okay; if not, it's new relay time.

Actually there are two ways to check that relay for proper function, one is to buy a new one and see if it cures the problem and the other is to check for voltage at pin 9. Since I don't go in for buying parts unless I need them, I chose the pin 9 route.

The other two relays had voltage where they were supposed to have it. Pink/blk, orange/black and orange all had voltage and the ground didn't light the tester, so the ground connection is okay.

I'm going to buy a new relay and see if it cures my intermittent problem. If not, I plan to check the lateral sensor, but I'll have to tear apart the dash to get to it UGGGGGGGH!

I checked the high amp wire and it showed voltage as it should, so that's okay.

And the saga continues . . .

Jake

 

The component between the white and green wire is a diode. The purpose of a diode is to only allow current flow in one direction.

In this case its purpose is turn on the Anti Lock indicator if the cable to the Control Module is disconnected. The other purpose is to allow the Control Module to control the Anti lock indicator.

When you first turn the ignition key to run (engine can be off) the Anti lock indicator comes on. Twelve volts is applied to the Control Module via the Module relay. The Control Module does a self test and also checks its input and output terminals.

This all takes place in less that one second. If the test passes, the Control Module will energize the Solenoid relay and the Anti lock indicator will turn off. This would confirm the Module relay, the Solenoid relay and Lateral Acceleration switch are good.

Does you system react this way?

The next test would take place when the vehicle starts to move. Once the vehicle speed is between 4 to 8 mph the Control Module does a dynamic test of the Modulator Valves, Pump motor and monitors the input from the wheel speed sensors.

You can tell when this test takes place when moving the car in reverse and applying light pressure on the brake pedal. You should hear the Pump motor come on. If you hear the motor, that tells you the Pump Motor and Pump Motor relay is good.

How does your system react during this test?

 

Hooked on Vettes knows Vette ABS. The diode is part of the control system to activate the ABS light on the dash. The way it is put together, it looks like a kludge by an incompetent previous owner, but it is just another example of fine GM 80's engineeering.

With a multi-meter or diode test tool you can test the diode to see that it is working correctly. It should have very high resistance in one direction and low resistance in the other. If not, the ABS light will remain on even if the system is ok.

What month magazine article did you find that outlines how to test the ABS relays?

 

Okay, here's what it does:

I turn the ignition key to "ON", but don't immediately start the engine; SES, Low Coolant and Anti-lock dash lights come on. Coolant and Anti-lock go off almost instantly, but SES stay ON.

I start the engine, same three come on but ALL go off almost instantly.

I back the car out of the garage down my 50 ft or so driveway and brake to a stop: No light at all.

I then shift to drive, accelerate slowly back into the garage and brake: Anti-Lock light comes on and stays ON.

Shut down the engine and restart and it does the whole thing all over again.

The magazine article is in Corvette Fever, May 2001; pages 62/64.

Any advice will be appreciated.

Thanks,

Jake

 

Oops, got to go back and check for the sound of the pump motor.

In the past I recall hearing it, but on the test I just did I didn't listen for it or hear it come on.

Back in a few . . .

Jake

 

Well does the pump come on?

If the pump comes on, you need to do the wheel sensor tests.

If the pump doesn't come on, you can test the pump by jumping 12 volts to it.

Remove the Pump Motor Relay. That's the black one mounted on top of the Modulator Valve.

With the relay removed, at the relay socket jump pins 87 to 30.

Pin 87 has 12 volts on it all of the time
Pin 30 is the lead to the Motor.

Touching these two pins together will energize the motor.

If you look at the bottom of the relay, it shows you the pin numbers.

 

Sorry I wasn't able to check on the pump motor operation; I had some guests stop by and I couldn't get away without being a worse host than I already am.

Thanks for that info. I'll try it later today. I'll post the results.

Jake

 

Well, I just did the test.

Pin 87 has 12 volts with the key either "On" or "Off".

When I jumped 87 to 30 I got a spark; motor did not come on.

I tried it twice with the same result. I then checked the gauges and brake fuses and neither was blown.

I hope that doesn't mean what I think it means.

Jake

 

Not good news.

Appears the motor is seized.

I've seen the used ABS pumps on E-bay for around $50.00. I believe 86-89 and maybe 90 are the same.

If you do change it, make sure you protect all surfaces from the brake fluid or you will need a paint job.

 

And I just finished painting the car (four times) too; that's all I need is to get brake fluid on it.

Well, I guess I'm in the market for another pump.

Jake

 

There's a pump on E-bay.

http://www.ebaymotors.com

Search on item 7959295172 3 hours to go.

$75.00

 

Thanks for that tip. I'm going to have to hold off for a few weeks before I buy another one, got to make this last college tuition payment for my daughter. She's up there in your neck of the woods; Harvard "ain't" cheap.

Jake

 

I have the exact same problem with my 87 Vette
the light goes on when i roll with the second diags test

When i jump the motor is engages and spins it doesn't seem to click in the solenoid and make pressure. It sounds like it is freewheeling like a starter does without catching the flywheel.

I took the caps off the relays so i can test the poles and see the relays work. Both seem to test OK on the bench and in the car.

The black relay clicks on and off a few times then stops and is open.

The light comes on only after i roll.

Could it be the solenoid for the pump motor?

I checked the plugs from the wheel sensors and they are all the same resistance. Is there a test i can do using those plugs? There are two wires from each wheel and a black wire.

 

Would love to find out more info on the 87 ABS also. I have had this same trouble for years, all sensors measure similar resistance, but the light comes on as soon as I start to move. Although she's been laid up a while now, this is one item I really need to fix when the engine goes back in.
Dave

 

I prepared a doc file of the ABS test procedure that was taken from an article in the May 2001 issue of Corvette Fever. The article also has photos, so if you can track it down the photos will help a lot.

If anyone wants a copy of the doc file I made, email me and I'll send it. jakejr266@sbcglobal.net

Jake

 

Thee actually three relays to check, the module relay, the pump motor relay and the solenoid relay. There's also a high amp circuit wire and a ground that should be checked.

You can check for voltage AFTER the relay at pin #9 of the module connector. If there's voltage there, the relay is good.

There are several wires that should be checked for the presence of voltage or, in once case, the absence of voltage (a ground wire.)

Be sure to remove each wheel sensor to check for and clean off any buildup on the sensor tips.

See my previous post for additional information.

Hope this helps.

Jake

 

Thanks for your help Jake. I have most copies of CF from years back, I will have to search through my old mags. My filing system is as good as my memory, it may take some time to surface. Dave