Trying to get ABS light out with no luck

[gstacky]

Hey guys, I have tried to follow all methods I could find on here, so no saying "search abs".
Here is what I've got so far:

Both the abs light and brake light were on. I checked the motor first by jumping the red/black wires, and it works, reconnected them.
Then checked the purple wire for power with key on, no brake pedal. Good to go.
Jumped the a and h in the aldl a few times, got the brake light to go out, but abs is still on.
I never got them both to come on and go out like I have read signifies a reset.
If I leave the a and h jumped, the abs light does blink, but barely. You can see it flicker a bit, but not flash on and off like I expected it too. Is this my problem? In the flicker, the only code it has is a 14, which is a normal abs code from what i've read and doesn't show any other codes. Any other ideas? I have yet to check the resistance at the aldl, but is there anything else to look for.
Any help is appreciated, it's my goal to get this fixed.

Greg

 

[gstacky]

Re: Trying to get ABS light out with no luck

It's on a 91. The light is normal brightness, and just dims a bit when flashing the code 14, so slight of a dim that you really have to look at it to see it, just a glance and you would never even notice. I'm thinking ground maybe? But everything else seems to work as it should, even when jumping a and h the motor cycles for a second like it should.

 

[alwayscode390]

Re: Trying to get ABS light out with no luck

Good question, my antilock and brake lights are both on too.

I was hoping a brake bleed would fix it since my master cylinder top flew off when pumping the brakes awhile back ( so it sucked in a LOT of air and spit out a LOT of fluid ) ... then both lights came on, lol ---

 

[gstacky]

Re: Trying to get ABS light out with no luck

Ok, so I had a minute last night and disconnected the 10 pin, and with key on, the abs light is out, plug it back in, and it's on again.
So you are thinking that this is a ground problem on the white/black wire Dave?

 

[waitn4]

Re: Trying to get ABS light out with no luck

I have this exact same problem. I know the ground for this ties into a ground on the back of the drivers side head. I have 4 volts on the aldl cable jumping A and H. Tomorrow I am going to examine the ground, but why would it read positive voltage if the was a ground problem? I just dont understand electricity. . .

Also, in the factory service manual if you are reading a voltage between 2-3 then it is the abs computer failing if the light disappears when unplugging the 10 pin connector. If the voltage reads 5 or greater then the ground mentioned above is the problem. I have 4 so I am going to try checking that ground tomorrow and then if that checks out I am buying a new abs computer.

 

[neildemo]

Re: Trying to get ABS light out with no luck

Great info Guys I have 2 trucks with this annoying light on will try everything you said.

 

[waitn4]

Re: Trying to get ABS light out with no luck

So I am trying to find G107, that is the system ground for the ecu, air conditioning and abs, and I cannot find where it attaches to the back of the head. It certainly does not help with having the wiring harness right in my way with only a few inches of space :rant: Does anyone have any idea on a trick to find that or how they got ahold of it?

 

[Rexxenexx]

Re: Trying to get ABS light out with no luck

Good stuff. Subscribing.

I have a similar prob. but my BPMV had a leaky gasket and drank water messing up the brain and (Hopefully only) the main section. It throws the relay something er other errors (ground problem) but we have good ground on the case which leads me to believe the prongs going from the brain to the inside of the main body are corroded to where they don't ground. Once we're done I'll post a new thread w a bunch of pics. Including repinning a 93 plug to accommodate a 92 brain and a dissection of the BPMV.

 

[waitn4]

Re: Trying to get ABS light out with no luck

I found the G107. It had been relocated in a much better location on the manifold. This was also connected on the same stud as the ground to the sheet metal. The nut on the stud was not very tight so I took it off and tested continuity. I got about 600 ohms from the 10 prong plug to the ground wire. This is not my problem. The only thing I can think is that the brain box acted up after the truck sat for a year. The abs worked great before it was parked.

As stated by the original poster, my abs light flashes codes but they are ground together and almost unreadable. I have checked all of the connections and I can only surmise that the issue is with the computer.

 

[waitn4]

Re: Trying to get ABS light out with no luck

If it IS 600 ohms, it may not be THE problem, but it IS a problem. Point-6 ohms, maybe, but no-way is 600 OK. Check it again.

Check terminal "A" (blk/wht) at the 10-pin to the alternator case for resistance. It should be way-less than 1 ohm. Like .03-.1 ohm. Wiggle the points of the leads into the metal, while watching the meter. Be sure you have a good connection. DVOM's are very sensitive. A bad "connection" at the meter lead will be misinterpreted as a fault in the circuit under test.

Check it again.
DaveP

I think the problem is my multi meter. I used the dial under 2k ohms and it read .6 and the dial goes down to 200 but when it does not even connecting the leads together is a number register it just reads 1 flat. How could a multimeter go bad like that?

 

[The Bronze]

Re: Trying to get ABS light out with no luck

I have this exact same problem. I know the ground for this ties into a ground on the back of the drivers side head. I have 4 volts on the aldl cable jumping A and H. Tomorrow I am going to examine the ground, but why would it read positive voltage if the was a ground problem? I just dont understand electricity. . .

Also, in the factory service manual if you are reading a voltage between 2-3 then it is the abs computer failing if the light disappears when unplugging the 10 pin connector. If the voltage reads 5 or greater then the ground mentioned above is the problem. I have 4 so I am going to try checking that ground tomorrow and then if that checks out I am buying a new abs computer.

I tried to follow this diagnostic pathway you are heading down and am confused.

Here is the diagnostic path:

The Pin H (diagnostic enable wire) should have a voltage of around 4-5 volts. I assumed you measured that with your meter from Pin H to Pin A. It reads positive because the meter is just measuring the difference in voltage. Until you apply a ground to the white wire Pin H, the voltage is still high. Once you ground it, the voltage should drop near 0 volts. If it doesn't drop, then you don't have a good ground at Pin A. You can follow that voltage until it does, or you can simply use a jumper wire and take Pin H to a real ground and retest voltage. The diagnostic steps from GM simply says:

1) that if the voltage is 0-1 volts when testing the circuit (ungrounded) that there is another path to ground prior to the ALDL connector on the white wire or the circuit is open.

2) If the voltage is between 1-5 volts (diagnostic connector not jumpered-which is enough to activate the test function of the PCM when grounded) then unplugging the 10-way connector (and the light stays on) that the problem is prior to the EHCU (something grounding the white wire), or:

3) If the voltage is between 1-5 volts (diagnostic connector not jumpered-which is enough to activate the test function of the PCM when grounded) then unplugging the 10-way connector (and the light goes out). If the light goes out, check the Disconnected Pin B wire and ensure that there is 12v there. If not, you have a circuit problem pulling that circuit to ground (as above) or if there is 12V then the EHCU is pulling the light to ground. That is the failure mode for the EHCU if it isn't powered up (verify that there is 12V at Pin A of the 10-way connector), If you then cannot get the EHCU to clearly flash the light then the EHCU is defective, or you are not doing it right.

In the real world, I would ground the test connector, and then watch the voltage on the Pin B and H of the 10-way connector. If the voltage did not go near ground, I would then look at the EHCU ground (Pin J). That is all that really controls the circuit, along with Pin A (power from brake fuse) and appropriate power to the bulbs (which you have since you said they illuminate just fine). Jumper a new ground to "J" if you can't test adequately.

Please note, that 12V does not equal 12V, it simply means roughly the actual battery voltage. If you battery is at 10V, please don't expect it to be higher than that at the test points. Please note that resistance is not used here. The computer doesn't care about that, only voltage/voltage drop. Please note that the red (red) goes on positive and black lead goes on negative or grounds. Please note you have to report back with the actual values you see and not "it was good" or "okay". Please note your mileage may vary. :2cents: :tup:

If you want a tool that can do all the above in about 1 minute, then get a powerprobe. Add a hyperlink here if you wish...

 

[waitn4]

Re: Trying to get ABS light out with no luck

I was able to borrow a nice fluke multimeter today and I can confirm something is screwy with my multimeter. Also the 200 ohm selection on it started working last night but the ohms it was reading are way off the fluke by about 20. I am never buying a crap multimeter again.

I was able to get a good reading on both the voltage at the aldl and measure the resistance in the ground at the 10 prong connector. The meter register 6ohms of resistance at the connector and the voltage read 4.42 volts jumpering A and H on the aldl. I did not connect the aldl to a separate ground.

To Bronze: The voltage when the 10 prong connector is connected to the ehcu reads 4.42 volts on the aldl. If the 10 prong connector is disconnected the voltage reads 0 at the aldl and the light goes out. The disconnected 10 prong connector reads voltages betweeen 11-12 on the ground wire connecting to all wires except the white wire that is for speed input. That wire reads nothing. You also referred to pin J, is that the white wire for speed input? The J pin on the 10 pin connector would have to be number 10 so it is either the pink/white ignition wire or it is the white speed input.

 

[The Bronze]

Re: Trying to get ABS light out with no luck

I was able to borrow a nice fluke multimeter today and I can confirm something is screwy with my multimeter. Also the 200 ohm selection on it started working last night but the ohms it was reading are way off the fluke by about 20. I am never buying a crap multimeter again.

If you don't worry about resistance, a cheap meter is usually within 1% for voltage and that is more than close enough. My trail bag has a $20 meter, as does my comm bag. I pull out the good one for calibrations only.

I was able to get a good reading on both the voltage at the aldl and measure the resistance in the ground at the 10 prong connector. The meter register 6ohms of resistance at the connector and the voltage read 4.42 volts jumpering A and H on the aldl. I did not connect the aldl to a separate ground.

If you provided a better ground, did the lights flash/PCM reset work as intented? Likely not as the ground was good enough to register the voltage difference and the circuit doesn't need much ground to work correctly.

To Bronze: The voltage when the 10 prong connector is connected to the ehcu reads 4.42 volts on the aldl. If the 10 prong connector is disconnected the voltage reads 0 at the aldl and the light goes out.

Good. Removing the 10 prong connector removes the ground path for the ABS light (and one path of ground for the BRAKE light). That means the EHCU is the reason the light is on.

The disconnected 10 prong connector reads voltages betweeen 11-12 on the ground wire connecting to all wires except the white wire that is for speed input. That wire reads nothing. You also referred to pin J, is that the white wire for speed input? The J pin on the 10 pin connector would have to be number 10 so it is either the pink/white ignition wire or it is the white speed input.

PIN J is the Black/White ground wire. PIN F is the white wire. That wire is the diagnostic enable wire. You know the one- it reads 4.42V at the aldl. It won't have voltage as it is generated at the EHCU. Speed inputs come from the ABS wheel speed sensors only. With the rest reading 12 volts, that means:

1) You have EHCU power on PIN A.( If you were missing this, you would be checking the brake fuse). Test=Good.
2) The ABS light ground on PIN B (it has power that is waiting on the EHCU to provide the ground to illuminate the light once you plug it back in- remember that until a ground is provided in an electrical circuit, there is power on both sides of the load (electrical device)). Test=Good.
3) PIN C. Purple wire. You have power through the brake switch (pedal is NOT depressed). Pressing the brake pedal would block power to the EHCU on this wire. Press the brake pedal and watch the power vanish. THEN Test=Good.
4) PIN D. Brown wire. Front axle switch. Funny, I didn't think this wire was there on a Syclone (I removed my harness). Someone else can verify. It does make sense as it wants to know if there is a connection between the two axles. I am too lazy to walk out to the garage to check the front axle or to perform a search. If it is there, then it should have battery voltage as well. Test=Good.
5) PIN E. Nothing.
6) PIN F. We discussed the diagnostic enable earlier. Test=Good.
7) PIN G. Nothing.
8) PIN H. Tan/White. This is the BRAKE light ground path. Same as #2. Should be power there unless the brake pressure switch trips or the E-brake is engaged. Engage e-brake, power should vanish. THEN Test=Good.
9) PIN J. Black/White. This is the EHCU ground wire. Super-duper important.

I would do this test a little differently. I would leave the unit plugged in. After all, isn't that how it normally works? Backprobe the wires to the EHCU. PIN A power? PIN B ground (mV reading) with the ABS light on/ Battery voltage with the ABS light commanded off? PIN C brake switch. Engage/disengage the brake pedal and watch the power cycle from battery voltage to 0.
PIN D. Ugh. somebody look that up or I will edit this tomorrow. :roll: PIN F About 5V with the ALDL NOT grounded. Ground it and it should drop near 0V. PIN H Grounded if the BRAKE light is illuminated. Battery Voltage if the light is off. PIN J Ground wire. With the system OPERATING, you should only see some mV (millivolts/ .xxxV) Nothing with a number to the left of the decimal!

Don't trust wiring to the ALDL? Just ground the white wire at the connector. You can clear the codes there as well doing the ground white wire for two seconds, remove for 1 second and then ground for 2 second procedure.

If the inputs are good and the EHCU won't pull/clear codes or flash the light by providing a GOOD solid gound path, then there is an internal fault.

<SOMEONE COULD INSERT THE GM ONE-PAGE WIRING DIAGRAM HERE>

EHCU is bad? Good; remove it and the rest of the ABS before you smack into the back of a van.