bwellard

Hi and thank you all in advance for your help.
It is a ’94 LT1 auto with 117k miles.
The “abs –inop” and the “brake” light are on. I purchased the car with the abs-inop problem and I had it scanned shortly after. The code came up as “abs motor pack short to positive”. I started to investigate the issue and have read and tried many of the procedures here. I have done the following:
Replaced the motor pack, tried two other EBCMs with the same result(the original is in the car now) , checked all grounds, abs sensors and connections, abs relay, continuity from the EBCM to the motor pack and used a pressure bleeder many times. I have dismantled the motor pack and turned the drive gears, then hooked the module up and turned the key and heard the motors cycle then bled the brakes again. After each procedure I would disconnect the battery cables to clear the codes. The only thing I have managed to change is the “BRAKE” light indicator now stays on all the time. I dismantled, cleaned and centered the differential valve and that didn’t correct the “Brake” indicator.
I decided to take it to the dealer to have it scanned and hear is the next problem.
The dealer report says:
No communication with the EBCM. Scan with tech 1 and found codes “1” and “4” ??? . Re scanned with tech 2 and found no codes but when function test was performed module lists codes. Also noted “EBCM communication POOR”.
Any suggestions???
Thanks again

GaryDoug

Do the lamps come on with the ignition switch or when the car starts to move? There are separate self tests that occur at those times. In either case I would check the connections at the power wires to the EBCM at both ends. I know that when the EBCM does it's system self tests and the 12v is drooping under the load, that can cause some false failures.

bwellard

YES all of the lamps (abs inop, brake and low trac) come on when the key is turned on. Once started the "low trac" light goes out. Nothing changes when the car starts to move. I will check all of the electrical connections and keep everyone posted.

bwellard

Ok, here is the latest.

After checking all of the obvious things I have ordered the suggested cable from amazon and downloaded the apps from GaryDoug. The cable should arrive sometime after 6/20.

Just to recap:
Abs inop and Brake lights in the instrument cluster are on all the time and the rear brakes will not keep the rear wheels from turning while the tires are lifted in the air and it is in gear.

I will keep everyone posted.

96m6lt1

You may need to pull your wheels of and clean the front reluctor rings Lt1s have this problem with age. I upgraded to the Ls1 brakes and hubs it solved my consistent inop light

Sent from my LG-P999 using Tapatalk 2

bwellard

Thanks for the response, Correct me if I am wrong, I thought the wheel sensors only turned the abs inop light on after the vehicle starts moving.

Barry

bwellard

Here is an update.

I purchased the USB to ALDL cable from Amazon and downloaded Scan9495 Free OBD1 scan app for 94-95 LT1. Installed the included driver for the ALDL cable and scanned the car. I only had three codes in the EBCM and they would clear and return in the blink of a eye.

The codes were:
63 - RF ABS motor short to ground
64 - Rear ABS motor short to open
86 - EBCM turned on the "BRAKE" warning light

I still doubt the abs motors are the problem because I have switched them out with different units and the DTC's did not change.

Any suggestions before I tear into the service manual flowcharts.

GaryDoug

You might check the condition of the large connector at the motor pack, and at the other end, the smaller connector at the EBCM. One other possibility is the ABS power enable relay in the underhood fuse box and/or the fusible link that supplies the power, at the wheelhouse junction near the battery.

bwellard

OK here is the latest. I have followed the GM service manual trouble shooting chart to the tee. All circuits from the EBCM to the ABS module are in good condition and ohm test within specs. If I follow the chart my next step is to swap out the EBCM. I did and my DTC's changed from 63, 64, & 86 to 61, 64, & 86. These codes cannot be cleared.
Did I swap out with another bad EBCM or do I actually have a another bad ABS motor pack.
Thanks for any advise.

GaryDoug

I am no expert here, but this is what I got when I did not have the balanced load on the motor outputs of my benchtop ABS/PCM setup (no real car) I noticed that if one was the wrong load (different from the others) it would cause failures for itself and the others as well.

bwellard

Thank you, how did you check for a balanced load on the motor outputs and what values should I see?

GaryDoug

When I say that, I mean that I was trying to put something on the motor drive outputs of my benchtop ABS setup in order to eliminate the trouble codes that occurred at power-up. I do not have a motor pack or pump assembly attached and have no intention of buying one any time soon. The "load" I am using is just an ordinary 20ma LED+1k resistor in series and those parts with another 1k ohm resistor in parallel overall (one set of these 3 parts for each of the 3 drivers). That has stopped the power-up setting of those trouble codes I showed. When I placed just one load on one output, the code for that output did not go away. It was only when I had all 3 loads attached that the codes disappeared. The point I was trying to make is that if there isn't at least a small load on each output and they are the same current drain, you will get those codes. So, I suspect you have an intermittent open circuit to the motor pack or inside the pack itself.

bwellard

Thank you for the clarification, I will double check all circuits from the EBCM to and including the motor pack.

bwellard

OK WE FIXED IT !!!

Thank you for all of your help. I couldn't have fixed it without GaryDoug's knowledge and programming skills. Thank You, Thank You, Thank You.

I had an open short on the rear (RR) motor circuit. And a bad EBCM. I tested the circuits by using the method below. I found the green wire in the 6 pin ABS module connector was not making contact (thanks to a good wiggle test). The circuit didn't have continuity. This made me happy that I finally found something wrong. I adjusted the pins in the ABS motor pack to correct the open circuit. I cleared the codes using GaryDoug's Program and still had a DTC #61. I knew the motor pack and the wire harness checked out within specs, I then changed the EBCM out with the unit I picked up from the wrecking yard, cleared the codes again. After several test drives I am smiling again.

Here is how I troubleshot the ABS motor pack and circuits from the EBCM at the same time.
1: Disconnect 8 pin connector from EBCM, use ohm meter to check resistance between pink and black wires.
2: Check resistance between green and orange wires.
3: Check resistance between purple and second black wires.

Note: Their is more than one black wire in the 8 pin connector so check the correct one. I used a Multimeter with Audible tone when continuity is present, This helps when you wiggle the wire harness and hear the tone.

Thank you all again.

Injuneer

Sometimes Gary is scary!



He never ceases to amaze me.

And, I'm going to copy this thread to the "Suspension, Chassis and Brakes" forum, and "Computer Diagnostics and Tuning" forum to make sure people can find it when they have a similar problem.