On vehicles equipped with anti-lock brakes (ABS), please refer to the appropriate procedure in a later section of this Section.
If any maintenance or repairs were performed on the brake system, or if air is suspected in the system, the system must be bled. If the master cylinder has been overhauled or if the fluid reservoir was run dry, start the bleeding procedure with the master cylinder. Otherwise (and after bleeding the master cylinder), start with the wheel cylinder which is farthest from the master cylinder (longest hydraulic line).
- If none of the above conditions apply, use standard bleed procedures.
- The auto bleed procedure is used on BOSH 5.3 equipped vehicles. This procedure uses a scan tool to cycle the system solenoid valves and run the pump in order to purge the air from the secondary circuits. These secondary 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 inside the BPMV to flow out toward the wheel cylinders or calipers where it can be purged out of the system.
- Inspect the battery for full charge, repair the battery and charging system, as necessary.
- Connect a scan tool to the data link connector (DLC) and select current and history DTCs. Repair any DTCs prior to performing the ABS bleed procedure. Inspect for visual damage and leaks and repair, as needed.
- Raise and vehicle on a suitable support.
- Turn the ignition switch to the OFF position.
- Remove all 4 tires.
- Connect the pressure bleeding tool according to the manufacturer's instructions.
- Turn the ignition switch to RUN position, engine off.
- Connect a scan tool and establish communications with the ABS system.
- Pressurize the bleeding tool to 30-35 psi (206-241 kPa).
Performing the Automated Bleed Procedure
NOTEThe Auto Bleed Procedure may be terminated at any time during the process by pressing the EXIT button. No further Scan Tool prompts pertaining to the Auto Bleed procedure will be given. After exiting the bleed procedure, relieve bleed pressure and disconnect bleed equipment per manufacturers instructions. Failure to properly relieve pressure may result in spilled brake fluid causing damage to components and painted surfaces.
- With the pressure bleeding tool at 30-35 psi (206-241 kPa), and all bleeder screws in closed position, select Automated Bleed Procedure on the scan tool and follow the instructions.
- The first part of the automated bleed procedure will cycle the pump and front release valves for one minute. After the cycling has stopped the scan tool will enter a cool down mode and display a 3 minute timer. The auto bleed will not continue until this timer expired, and cannot be overridden.
- During the next step, the scan tool will request the technician to open one of the bleeder screws. The scan tool will then cycle the respective release valve and pump motor for one minute.
- The scan tool will repeat step 3 for the remaining bleeder screws.
- With the bleeder tool still attached to the vehicle and maintaining 30-35 psi (206-241 kPa), the scan tool will instruct the technician to independently open each bleeder screw for approximately 20 seconds. This should allow any remaining air to be purged from the brake lines.
- When the automated bleed procedure is completed the scan tool will display the appropriate message.
- Install all 4 tires.
- Remove pressure from the pressure bleeding tool and then disconnect the tool from the vehicle.
- Depress the brake pedal to gage pedal height and feel. Repeat steps 1-8 until the pedal is acceptable.
- Remove the scan tool from the DLC connector.
- Lower the vehicle.
- Inspect the brake fluid level in master cylinder.
- Road test the vehicle while making sure the brake pedal remains high and firm.
- If the vehicle is equipped with a traction control system (TCS), the scan tool will cycle both the ABS and the TCS solenoid valves. This bleed procedure is the same as above.