The base brake's hydraulic system must be bled anytime air enters the hydraulic system. The ABS though, particularly the Hydraulic Control Unit (HCU), should only need to be bled when the 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 requires bleeding 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.
- Make sure all hydraulic fluid lines are installed and properly torqued.
- Connect the DRBIII® scan tool, or equivalent, to the Data Link Connector (DLC). The connector is located under the lower steering column cover to the left of the steering column.
Using the scan tool, check to make sure the CAB does not have any fault codes stored. If it does, clear them using the scan tool.
CAUTIONWhen bleeding the brake system wear safety glasses. A clear bleed tube must be attached to the bleeder screws and submerged in a clear container filled part way with clean brake fluid. Direct the flow of brake fluid away from yourself and the painted surfaces of the vehicle. Brake fluid at high pressure may come out of the bleeder screws when opened.
- Bleed the base brake system using the standard pressure or manual bleeding procedure. Refer to Base Brake Bleeding procedure in this section.
- Using the DRBIII® scan tool, or equivalent, 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.