ABS module

Tiny
THOMAS JAMES CRAVALHO
  • MEMBER
  • 2004 CHEVROLET SILVERADO
  • 4.8L
  • V8
  • 4WD
  • AUTOMATIC
  • 90,000 MILES
How can I get air out of the ABS module without scan tool?
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Sunday, July 10th, 2016 AT 9:24 AM

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Tiny
CARADIODOC
  • EXPERT
If we are to assume there really is air trapped in a chamber, you need to open that valve to let the air out, but there has to be brake fluid under pressure ready to take its place. Scanners will command the controller to run the pump or pressurize the fluid. Scanners are used for that because it is much easier than the alternative. The computer will open each valve. That alternative is to unplug the connector, then apply ground and 12 volts to the two wires for each solenoid. That would take a long time and may not be very effective.

First you need to tell me why you want to bleed the system so I am in the right frame of mind. I have a number of tricks to get air out of any system without bleeding at the wheels. If you can get the hydraulic controller to kick in, let it keep on activating until the vehicle comes to a stop, but keep on holding the brake pedal down in the same position. Try very hard to never ever push the brake pedal more than halfway to the floor as that can damage a master cylinder from crud and corrosion if it is more than about a year old. Wait like that for about ten seconds, then let the brake pedal snap back quickly on its own.

While the valves are being pulsed, you'll be pushing brake fluid down to them, and if you are lucky, the air will come out of the chambers and float upward. The ten seconds is to let them float up as much as possible. Releasing the brake pedal quickly will make the brake fluid rush back to the reservoir and wash the air bubbles up with it. Stroking the brake pedal 1/4 way down can do that too. Push it very slowly so the air bubbles keep on floating up. Release quickly to wash the bubbles up. You don't have to be concerned with which wheel(s) skid during the stop. Individual wheel valves only block fluid flow momentarily when activated in a skid. Those wont trap air.

That pedal stroking also works as a secondary method after replacing the master cylinder.

There are wiring diagrams further down on this post that can help you activate the valves manually.
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Sunday, July 10th, 2016 AT 8:04 PM
Tiny
8592795367
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I have a 2001 gmc dually 6.6l turbo diesel. How can I manually bleed the abs pump or and module
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Sunday, October 8th, 2017 AT 9:15 PM
Tiny
CARADIODOC
  • EXPERT
Here is a wiring diagram for the ABS (BELOW) to figure out which wires are for each solenoid, then apply 12 volts and ground to apply them, then do the normal bleeding. YOU might be smart enough to figure out how to make that work, but I'm not. In normal operation during a skid, the computer pulses the various solenoids on and off very quickly, and for only a few seconds. With a scanner, the bleeding process is over almost as fast as you can push the buttons. If you were to apply 12 volts, I'd be concerned a solenoid could become overheated if it is kept applied too long.

Also be aware some solenoid-controlled valves are normally open, and they block fluid flow when applied, ("block" valves), and some are normally closed, and open to pass fluid when turned on, ("dump" valves). We don't know which valves to apply power to or if multiple valves have to be energized at the same time. Some engineer much smarter than us figured that out, then programmed their scanners to do it.

What you might consider is turning the ignition switch on while you're in the middle of bleeding. Most ABS Computers exercise the valves during the six-second self-test process when the yellow warning light is on. I could envision doing that two or three times, and that might be enough to expel air from the chambers. The self-test might be aborted if the computer sees you have the brake pedal applied, so consider pushing the brake pedal two or three seconds after you turn on the ignition switch. That might be enough to push any released air bubbles further down the line, then they can be bled out the rest of the way like normal. Have the bleeder screws open so fluid and air can flow down the lines and away from the valves.

Remember to never push the brake pedal over half way to the floor. Crud and corrosion build up in the lower halves of the bores where the pistons in the master cylinder don't normally travel. Pushing the pedal over half way runs the rubber lip seal over that crud and can rip them. That can result in a slowly-sinking brake pedal, and that often doesn't show up until two or three days later.
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Monday, October 9th, 2017 AT 9:28 PM
Tiny
8592795367
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So pretty much I have to either use the brake peddle and only go half way like I was bleeding the brakes at the wheels or ur 12 volts on it but not for long period of time. And my brake peddle is spongy and goes to the floor does that matter or still just pump the brakes peddle only half way with each pump. Also is driving the truck and making it go in to an abs skid out of the question or do you think it wouldn't hurt to try it.
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Thursday, October 12th, 2017 AT 10:24 AM
Tiny
CARADIODOC
  • EXPERT
You won't get the tires to skid if the brake pedal is mushy. Even if you could, you wouldn't be driving with the bleeder screws open, so no fluid, or the air in it, is going to flow out of the chambers. The fluid and air would just pulsate back and forth.

When you have a nail that needs to be smacked, you need a hammer. When you're stumbling around in the dark, you need a light bulb. When you need to bleed the ABS system, you need a scanner.

As for running the brake pedal all the way to the floor, my warning does not apply to any master cylinder that is less than about a year old. Also, if you've already done that, if a seal was going to be damaged, it has happened already. If no seal was damaged, it is a good bet none will be damaged in the near future from your bleeding attempts.
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Thursday, October 12th, 2017 AT 7:56 PM

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