Brake system trouble codes?

[sofasurfer]

I was told that the ABS system produces trouble codes which are accessible through the ALDL. Can you tell me if this is true and what pins I jump to read them and where to find explainations for the codes?
Thanks.

 

[Molson02536]

I was told that the ABS system produces trouble codes which are accessible through the ALDL. Can you tell me if this is true and what pins I jump to read them and where to find explainations for the codes?
Thanks.

It can be done with a OBDI system and not with a OBDII system. The OBDII system started in 1996 vehicles and newer.

On a typical General Motors application with a Bosch 2U ABS system (1990-94 fullsize rear-wheel drive passenger car), for example, codes can be accessed manually by grounding terminal "H" on the ALDL connector, then counting flashes of the ABS lamp. On these systems, flash codes repeat three times. Codes will stay in memory 50 ignition cycles. But to clear codes, you need a scan tool.

On ABS systems that provide manual flash codes (such as Bosch 2E, 2S, 2U and 3, Kelsey-Hayes RWAL and 4WAL, and ITT Teves Mark 2), you do not need a scan tool but using one reduces the chance of misreading a code.

http://www.troublecodes.net/GM/

The ABS brake system has separate diagnostics. Here's how to do the ABS system diagnostic test:

Turn the ign switch to the "ON" position. Jump terminal "H" to terminal "A" of the DLC (AKA ALDL) and count the number of "ANTILOCK" lamp flashes. The terminals must be jumped for a few seconds before the DTC (Diagnostic Trouble Code) will begin to flash. Here's an example: if the lamp flashes twice <pause> once, then that indicates DTC 21 which is listed as "Right Front Wheel Speed Sensor or Circuit Open (Static)".

If the ABS system is working properly then codes 12, 13, 14 or 15 will display depending on whether 2WD/4WD & whether brake pedal is released/applied.

Here's the procedure for clearing ABS codes:
1. Turn the ign switch to the "ON" position.
2. Use a jumper wire to ground DLC terminal "H" to "A" for 2 seconds.
3. Remove the jumper wire for 1 second.
4. Repeat the grounding for 2 seconds.
5. An indication of success is when the "ANTILOCK" and "BRAKE" lamps turn on and then turn off.

All of the above is directly from my '95 FSM.

Pin A, the ground, is the topmost right corner pin & pin H is one pin over from the bottom left corner. Keep us posted.

 

[sofasurfer]

Hmmm...
I jumpered the correct pins and turned the key on and the check engine light just stayed on solid. Am I missing something?

And just in case I make progress, where you say, "Here's the procedure for clearing ABS codes:", shouldn't the jumper be in place BEFORE I turn to ignition on?

Just out of curiosity, what will happen if I install or remove the jumper with the ignition turned on? I ask because I started my truck with the jumper across A&B a couple times.

 

[Molson02536]

Hmmm...
I jumpered the correct pins and turned the key on and the check engine light just stayed on solid. Am I missing something?

And just in case I make progress, where you say, "Here's the procedure for clearing ABS codes:", shouldn't the jumper be in place BEFORE I turn to ignition on?

Just out of curiosity, what will happen if I install or remove the jumper with the ignition turned on? I ask because I started my truck with the jumper across A&B a couple times.

To clear the ABS, the ignition needs to be on already. just follow the instructions and take your time.

Post me back if you have any more questions, be glad to help.

GM vehicles made before 1995, the diagnostic connector is located under the dash panel by the driver side. To get the check engine codes to flash in your dash panel, use a jumper wire or a paper clip and connect terminals A and B of the diagnostic connector. Turn your ignition key on with engine off and the codes should start to blink. All codes should start with code 12 which is one long flash followed by 2 short flashes. This code 12 means the diagnostic system is normal and will repeat itself continuously if there are no trouble codes. Otherwise, code 12 will flash 3 times before flashing the fault codes.

 

[sofasurfer]

I just want to clarify, I neglected to say in this thread that I have a 95 Sierra.

 

[sofasurfer]

O, this is weird.
I turned on the ignition switch. I put the jumper in the "A" pin and then touched it to the "H" pin. I heard a noise that I thought was a gun way off in the distance. I did it again...Theres that dang gun again, and my fuel pump started to run for about 5 seconds. Or maybe its fire works. I touched it again. Again, the gun, but this time I noticed it is coming from under the hood. Every time I touch the "H" pin I heard the pounding or muffled banging noise from under the hood, and every time the fuel pump runs for 5 seconds or so. I opened the hood but I can not tell where the sound comes from since I am under the dash.

The ABS light did go out but it came right back on again when I removed the jumper. Is that how it should be?

You said,"An indication of success is when the "ANTILOCK" and "BRAKE" lamps turn on and then turn off". You are saying it turns ON and then OFF, however, mine is always ON.

 

[Molson02536]

O, this is weird.
I turned on the ignition switch. I put the jumper in the "A" pin and then touched it to the "H" pin. I heard a noise that I thought was a gun way off in the distance. I did it again...Theres that dang gun again, and my fuel pump started to run for about 5 seconds. Or maybe its fire works. I touched it again. Again, the gun, but this time I noticed it is coming from under the hood. Every time I touch the "H" pin I heard the pounding or muffled banging noise from under the hood, and every time the fuel pump runs for 5 seconds or so. I opened the hood but I can not tell where the sound comes from since I am under the dash.

The ABS light did go out but it came right back on again when I removed the jumper. Is that how it should be?

You said,"An indication of success is when the "ANTILOCK" and "BRAKE" lamps turn on and then turn off". You are saying it turns ON and then OFF, however, mine is always ON.

Sorry for just getting back to you, work thing. You may have the OBD1.5 system in your Sierra and your going to need a scanner for that, Auto Zone can scan free of charge and Parts Source in Canada.

Keep me posted and recheck to make sure you are grounding the right terminals. Bottom left terminal G - Fuel Pump is your fuel pump data link and right next to it to the right is your H - Brake Sense Speed Input.