CTS 2003-2005

Bleeding the ABS System

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Before performing the ABS Automated Bleed Procedure, first perform a pressure bleed of the base brake system. The automated bleed procedure is recommended when one of the following conditions exist:

  1. The base brake system does not achieve the desired pedal height or feel.
  2.  
  3. Extreme loss of brake fluid has occurred.
  4.  
  5. Air ingestion is suspected in the secondary circuits of the brake modulator assembly.
  6.  

The ABS Automated Bleed Procedure uses a scan tool to cycle the system solenoid valves and run the pump in order to purge any air from the secondary circuits. These circuits are normally closed off, and are only opened during system initialization at vehicle start up and during ABS operation. The automated bleed procedure opens these secondary circuits and allows any air trapped in these circuits to flow out toward the brake corners.

  1. Raise the vehicle on a suitable support.
  2.  
  3. Remove all four tire and wheel assemblies.
  4.  
  5. Inspect the brake system for leaks and visual damage.
  6.  
  7. Inspect the battery state of charge.
  8.  
  9. Install a scan tool.
  10.  
  11. Turn ON the ignition, with the engine OFF.
  12.  
  13. With the scan tool, establish communications with the electronic brake control module (EBCM). Select Special Functions. Select Automated Bleed from the Special Functions menu.
  14.  
  15. Bleed the base brake system.
  16.  
  17. Follow the scan tool directions until the desired brake pedal height is achieved.
  18.  
  19. If the bleed procedure is aborted, a malfunction exists. Perform the following steps before resuming the bleed procedure:
    1. If a DTC is detected, check for the cause and repair as necessary.
    2.  
    3. If the brake pedal feels spongy, perform the conventional brake bleed procedure again.
    4.  

  20.  
  21. When the desired pedal height is achieved, press the brake pedal in order to inspect for firmness.
  22.  
  23. Remove the scan tool.
  24.  
  25. Install the tire and wheel assemblies.
  26.  
  27. Inspect the brake fluid level.
  28.  
  29. Road test the vehicle while inspecting that the pedal remains high and firm.
  30.  


CAUTION
Use only GM SUPREME 11 (GM #1052542) or equivalent DOT 3 brake fluid from a clean, sealed container. Do not use fluid from an open container that may be contaminated with water. Improper or contaminated fluid could result in damage to components or loss of braking, with possible personal injury.


WARNING
Overfilling the brake fluid reservoir must be avoided due to the potential for overflow onto the nearby catalytic converters in the exhaust system. Brake fluid is flammable, and contact with hot exhaust components could result in a fire and possible personal injury. Do NOT allow brake fluid to spill on or come in contact with the vehicle's finish as it will remove the paint. In case of a spill, immediately flush the area with water.


NOTE
If any brake component is repaired or replaced such that air is allowed to enter the brake system, the entire bleeding procedure MUST be followed. Prior to bleeding the brakes, the front and rear displacement cylinder pistons must be returned to the topmost position. The preferred method uses a Tech 1® or equivalent scan tool to perform the rehoming procedure. If a scan tool is not available, a second procedure may be used, but it is extremely important that the procedure be followed exactly as outlined.

A bleeding operation is necessary to remove air when it has been introduced into the hydraulic brake system (by disconnecting brake lines or if the brake fluid reservoir has been allowed to run dry).

It is necessary to bleed the system at all four brakes. If a brake hose or steel brake line has been disconnected at one wheel, only that wheel caliper (or wheel cylinder, as equipped) needs to be bled. If brake lines or hoses are disconnected at any fitting located between the master cylinder and the brakes, then the brake system served by the disconnected brake line must be bled.

Before bleeding the ABS brake system, the front and rear displacement cylinder pistons must be returned to the topmost position. The preferred method uses a Tech 1® or T-100® scan tool to perform the rehoming procedure. If a Tech 1® is not available, the second procedure may be used, but it must be followed EXACTLY.

Manual Bleeding





Click image to see an enlarged view

Fig. ABS hydraulic modulator/master cylinder bleeder locations

  1. Clean the master cylinder fluid reservoir cover and surrounding area, then remove the cover.
  2.  
  3. Add fluid, if necessary to obtain a proper fluid level, then put the reservoir cover back on.
  4.  
  5. Prime the ABS hydraulic modulator/master cylinder assembly as follows:
    1. Attach a bleeder hose to the rearward bleeder valve, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
    2.  
    3. Slowly open the rearward bleeder valve.
    4.  
    5. Depress and hold the brake pedal until the fluid begins to flow.
    6.  
    7. Close the valve, then release the brake pedal.
    8.  
    9. Repeat Steps 3b-3d until no air bubbles are present.
    10.  
    11. Relocate the bleeder hose to the forward hydraulic modulator bleeder valve, then repeat Steps 3a-3e7.
    12.  

  6.  
  7. Once the fluid is seen to flow from both modulator bleeder valves, the ABS modulator/master cylinder assembly is sufficiently full of fluid. However, it may not be completely purged of air. At this point, move to the wheel brakes and bleed them. This ensures that the lowest points in the system are completely free of air and then the assembly can purged of any remaining air.
  8.  
  9. Remove the fluid reservoir cover. Fill to the correct level, if necessary, then fasten the cover.
  10.  
  11. Raise and safely support the vehicle.
  12.  
  13. Proceed, as outlined in the following steps, to bleed the wheel brakes in the following sequence: right rear, left rear, right front, then left front.
    1. Attach a clear plastic bleeder hose to the bleeder valve at the wheel, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
    2.  
    3. Open the bleeder valve.
    4.  
    5. Have an assistant slowly depress the brake pedal.
    6.  
    7. Close the valve and slowly release the release the brake pedal.
    8.  
    9. Wait 5 seconds.
    10.  
    11. Repeat Steps 7a-7e until the brake pedal feels firm at half travel and no air bubbles are observed in the bleeder hose. To assist in freeing the entrapped air, tap lightly on the caliper or braking plate to dislodge any trapped air bubbles.
    12.  

  14.  
  15. Repeat Step 7 for the remaining brakes in the sequence given earlier.
  16.  
  17. Carefully lower the vehicle.
  18.  
  19. Remove the reservoir cover, then fill to the correct level with brake fluid and replace the cap.
  20.  
  21. Bleed the ABS hydraulic modulator/master cylinder assembly as follows:
    1. Attach a clear plastic bleeder hose to the rearward bleeder valve on the modulator, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
    2.  
    3. Have an assistant depress the brake pedal with moderate force.
    4.  
    5. Slowly open the rearward bleeder valve and allow the fluid to flow.
    6.  
    7. Close the valve, then release the brake pedal.
    8.  
    9. Wait 5 seconds.
    10.  
    11. Repeat Steps 11a-11e until no air bubbles are present.
    12.  
    13. Relocate the bleeder hose to the forward hydraulic modulator bleeder valve, then repeat Steps 11a-11f.
    14.  

  22.  
  23. Carefully lower the vehicle, then check the brake fluid and add if necessary. Secure the reservoir cap to the reservoir.
  24.  
  25. With the ignition switch placed in the RUN position, apply the brake pedal with moderate force and hold it. Note the pedal travel and feel. If the pedal feels firm and constant and the pedal travel is not excessive, start the engine. With the engine running, recheck the pedal travel. If it's still firm and constant and pedal travel is not excessive, road test the vehicle and make sure the brakes are operating properly.
  26.  
  27. If the pedal feels soft or has excessive travel either initially or after the engine is started, the following procedure may be used:
    1. With the Tech 1® or equivalent scan tool, RELEASE then APPLY each motor 2-3 times and cycle each solenoid 5-10 times. When finished, be sure to APPLY the front and rear motors to ensure the pistons are in the upmost position. DO NOT DRIVE THE VEHICLE.
    2.  
    3. If a Tech 1® or equivalent scan tool is not available, remove your foot from the brake pedal, start the engine and allow it run for at least 10 seconds to initialize the ABS. DO NOT DRIVE THE VEHICLE. After 10 seconds, turn the ignition switch to the OFF position. The initialization procedure most be repeated 5 times to ensure any trapped air has been dislodged.
    4.  
    5. Repeat the bleeding procedure, starting with Step 1.
    6.  

  28.  
  29. Road test the vehicle, and make sure the brakes are operating properly.
  30.  

Pressure Bleeding





Click image to see an enlarged view

Fig. ABS pressure bleeding components



Click image to see an enlarged view

Fig. Position a shop rag to catch escaping brake fluid


NOTE
The pressure bleeding equipment must be of the diaphragm type. It must have a rubber diaphragm between the air supply and the brake fluid to prevent air, moisture and other contaminants from entering the hydraulic system.

  1. Clean the master cylinder fluid reservoir cover and surrounding area, then remove the cover.
  2.  
  3. Add fluid, if necessary to obtain a proper fluid level.
  4.  
  5. Connect bleeder adapter J 35589, or equivalent, to the brake fluid reservoir, then connect the bleeder adapter to the pressure bleeding equipment.
  6.  
  7. Adjust the pressure bleed equipment to 5-10 psi (35-70 kPa) and wait about 30 seconds to be sure there is no leakage.
  8.  
  9. Adjust the pressure bleed equipment to 30-35 psi (205-240 kPa).
  10.  


WARNING
Use a shop rag to catch the escaping brake fluid. Be careful not to let any fluid run down the motor pack base or into the electrical connector.

  1. With the pressure bleeding equipment connected and pressurized, proceed as follows:
    1. Attach a clear plastic bleeder hose to the rearward bleeder valve on the hydraulic modulator.
    2.  
    3. Slowly open the bleeder valve and allow fluid to flow until no air is seen in the fluid.
    4.  
    5. Close the valve when fluid flows out without any air bubbles.
    6.  
    7. Repeat Steps 6b and 6c until no air bubbles are present.
    8.  
    9. Relocate the bleeder hose on the forward hydraulic modulator bleed valve and repeat Steps 6a through 6d.
    10.  

  2.  
  3. Tighten the bleeder valve to 80 inch lbs. (9 Nm).
  4.  
  5. Proceed to bleed the hydraulic modulator brake pipe connections as follows with the pressure bleeding equipment connected and pressurized:
    1. Slowly open the forward brake pipe tube nut on the hydraulic modulator and check for air in the escaping fluid.
    2.  
    3. When the air flow ceases, immediately tighten the tube nut. Tighten the tube nut to 18 ft. lbs. (24 Nm).
    4.  

  6.  
  7. Repeat Steps 8a and 8b for the remaining three brake pipe connections moving from the front to the rear.
  8.  
  9. Raise and safely support the vehicle.
  10.  
  11. Proceed, as outlined in the following steps, to bleed the wheel brakes in the following sequence: right rear, left rear, right front, then left front.
    1. Attach a clear plastic bleeder hose to the bleeder valve at the wheel, then submerge the opposite hose end in a clean container partially filled with clean brake fluid.
    2.  
    3. Slowly open the bleeder valve and allow the fluid to flow.
    4.  
    5. Close the valve when fluid begins to flow without any air bubbles. Tap lightly on the caliper or backing plate to dislodge any trapped air bubbles.
    6.  

  12.  
  13. Repeat Step 11 on the other brakes using the earlier sequence.
  14.  
  15. Remove the pressure bleeding equipment, including bleeder adapter J 35589, or equivalent.
  16.  
  17. Carefully lower the vehicle, then check the brake fluid and add if necessary. Secure the reservoir cap onto the reservoir.
  18.  
  19. With the ignition switch turned to the RUN position, apply the brake pedal with moderate force and hold it. Note the pedal travel and feel. If the pedal feels firm and constant and the pedal travel is not excessive, start the engine. With the engine running, recheck the pedal travel. If it's still firm and constant and pedal travel is not excessive, go to Step 17.
  20.  
  21. If the pedal feels soft or has excessive travel either initially or after the engine is started, the following procedure may be used:
    1. With the Tech 1® or equivalent scan tool, RELEASE then APPLY each motor 2-3 times and cycle each solenoid 5-10 times. When finished, be sure to APPLY the front and rear motors to ensure the pistons are in the upmost position. DO NOT DRIVE THE VEHICLE.
    2.  
    3. If a Tech 1® or equivalent scan tool is not available, remove your foot from the brake pedal, start the engine and allow it run for at least 10 seconds to initialize the ABS. DO NOT DRIVE THE VEHICLE. After 10 seconds, turn the ignition switch to the OFF position. The initialization procedure most be repeated 5 times to ensure any trapped air has been dislodged.
    4.  
    5. Repeat the bleeding procedure, starting with Step 1.
    6.  

  22.  
  23. Road test the vehicle, and make sure the brakes are operating properly.
  24.  

Rehome Procedure



With Tech 1® Or T-100® Or Equivalent Scan Tools
  1. Using a Tech 1® or T-100® (CAMS), select "Motor Rehome." The motor rehome function cannot be performed if current DTCs are present. If DTCs are present, the vehicle must be repaired and the codes cleared before performing the motor rehome function.
  2.  
  3. The entire brake system should now be bled using the pressure or manual bleeding procedures outlined later in this section.
  4.  

Wthout Tech 1® Or T-100® R Equivalent Scan Tools

NOTE
Do not place your foot on the brake pedal through this entire procedure unless specifically instructed to do so.

This method can only be used if the ABS warning lamp is not illuminated and no DTCs are present.

  1. Remove your foot from the brake pedal.
  2.  
  3. Start the engine and allow it to run for at least 10 seconds while observing the amber ABS warning lamp.
  4.  
  5. If the ABS warning lamp turned ON and stayed ON after about 10 seconds, the bleeding procedure must be stopped and a Tech 1® or equivalent scan tool must be used to diagnose the ABS function.
  6.  
  7. If the ABS warning lamp turned ON for about 3 seconds, then turned OFF and stayed OFF, turn the ignition switch to the OFF position.
  8.  
  9. Repeat Steps 1-4 one more time.
  10.  
  11. The entire brake system should now be bled by following the manual or pressure bleeding procedure.
  12.  

 
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