1988 coupe auto

My ABS light has been on for a while. The ABS doesn't perform a test when first moving.

A friend lent me a Kent Moore ABS tester.

When I connected it & turned ignition on, there was no power to the tester.

The FSM says to check the ABS Module relay connector.

I got the correct result for tests 1-3 but on test 4 no voltage

Test 4 should show battery voltage between the GREY/BLK and the BLK.

I also tested the GRY/BLK straight to the negative battery terminal and no voltage

Looking at the schematics in the electrical section,this GRY/BLK goes directly to the Ignition On Input of the ABS control module.

I don't see what to test after that.

Any suggestions please?

Also the Kent Moore tester was bought on ebay and this is the first time it's been plugged in - is there any way to test that it is working? (apart from plugging it into another vette!)

 

Does the ABS light come on and stay on or does it go off after the car is started then go on again after the vehicle is moving?

 

The ABS light is on all the time, there is no self test when first moving at 3-6mph. The ABS was working fine for several years, then went totally dead and h been like that for 18 months.

I have checked all the fuses and followed the FSM instructions

I am following through the FSM test procedures and if the Kent Moore tester doesn't show a power up message the possible cause is No Battery Voltage to ABS Tester or Open ABS Ground circuit.

Ther Repair action is Do test A

Test A is the Module Relay Test, page 8A-44-9.
Tests 1,2 & 3 all give the correct result, test 4 shows zero on the multimeter when it should show battery voltage.

I confirmed the BLK is connected to ground, I'm unsure what to test next.

BTW the suggestion if test 4 fails is, 'Replace Module Relay' - now this isn't logical because I have removed the relay and am testing the wires at the connector. If test 4 fails that means the relay is not receiving a signal from the ABS control Module, so how can fitting a new one make any difference?

also when ignition is first turned on the brake warning light does NOT light. The globe is OK because the handbrake makes it come on. I'm fairly sure that this light should show for a few seconds to confirm it's working. Don't know if that and the ABS not working are related. Please can someone confirm that the brake warning light does show when turning the ignition on?

 

Sorry, I thought that I could work through it with you. I am doing my 1986 right now (light isn't on until the car moves at the testing speed then it comes on) Anyway, the 1986 manual only shows 3 tests and the wiring colors are different.

I will look around to see what I can find.

 

That's OK, appreciate any help I can get- I need an ABS or electrics guru I think - hope someone see's my post

 

Check the ground to make sure it makes contact

 

Test 4 is done with the Control Module relay installed in its
socket.

When you turn the ignition On, the Anti Lock light should light for less than a second and then go out which indicates the ABS module self
test has passed.

Turn the ignition key to On. Very slowly turn the key towards the
Start position. Before you get to the Start position, a bulb test
is done. The Brake light bulb should light and the Anti Lock
indicator should also light as long as you hold the key in
the position between Run and Start.

If this test works, the ABS Control module has 12 volts going to it
on Pin 1.

As for the ABS Kent Moore tester, you can manually apply 12 volts and ground to it and verify the tester powers up.

The Kent Moore test connector looks like this.
Apply ground to pin 34.
Apply 12 volts to pin 1.

 

Hooked on Vettes - THANK YOU!!!!!

The Kent Moore tests OK, much appreciate the picture to show which pins are #1 & #34

There is no voltage between BLK and GRY/BLK - therefore the relay is faulty.

I knew diagnosis 4 didn't make sense, I missed the instruction to connect the relay - now it makes perfect sense.

I may find further problems when I replace the relay, but I'm back on track and very grateful.

I have some spare MAF burnoff relays, will they work is is this relay specific to the module?

 

That's not a standard relay.

It has a zener diode from pin 87 to pin 31 of
the relay. The diode protects the Control Module
from high input voltage.

It also has a diode on pin 15 input of the relay coil.

Disconnect the negative battery terminal because
the Brake 10amp fuse is hot all the time.

Remove the Control Module relay and pry the
cover off. Look at the output contacts. Maybe
you can file the contacts so they work if that's
why there is no 12 volts coming out of it.

For test purposes you can remove the relay and
jump the Orange/Black wire at the relay socket
to the Gray/Black wire. This will allow the 12 volts
to get to the Control Module. (Leave relay out of
the relay socket).

You can then attach the Kent Moore tester, reconnect
the battery and continue your testing.

 

Thank you again Hooked on Vettes, that is exactly the kind of information I appreciate. I'm about to go away for a few days, I will try those things next week and report back.

 

Thanks again Hooked on Vettes- I did the jumper as you suggested and my ABS worked!!

I had a lot of trouble finding the relay online to ship to me here in Australia. Finally an electronic wizz friend of mine tested the relay and found the solenoid had burnt out.

He fitted a new solenoid and I now have my ABS working Wooohooo it's such a great feeling when you fix something!!

 

Troubleshooting my ABS today and had the same issue. Hooked up my ABS test set and no lights came on. Troubleshooted the control module relay as described in my FSM and no power on the grey/blk wire with the relay reconnected.

Performed the jump test and my ABS tester came to life.

Thanks for the valuable insight.

 

if the tester doesn’t light up check your ground at the connector c413 both black wire.

look if you have 12v at pin 1 on your ebcm connector