The base brake's hydraulic system must be bled anytime air enters the hydraulic system; follow the Conventional Bleeding Procedure. The ABS system though should only need to be bled when the Hydraulic Control Unit (HCU) is replaced or removed from the vehicle. The ABS must always be bled anytime it is suspected that the HCU has ingested air. Under most circumstances that require the bleeding of the brakes hydraulic system, only the base brake hydraulic system needs to be bled.
When bleeding the ABS system, the following bleeding sequence must be followed to insure complete and adequate bleeding:
- Bleed the base brake system using the standard manual bleeding procedure.
- Using the scan tool, select ANTILOCK BRAKES, followed by MISCELLANEOUS, then BLEED BRAKES. Follow the instructions displayed. When the scan tool displays TEST COMPLETED, disconnect the scan tool and proceed.
- Bleed the base brake system a second time. Check brake fluid level in the reservoir periodically to prevent emptying, causing air to enter the hydraulic system.
- Fill the master cylinder reservoir to the full level.
- Test drive the vehicle to be sure the brakes are operating correctly and that the brake pedal does not feel spongy.