Bleeding the Brake System (ABS)
Auto Bleed Procedure
Perform a manual bleeding procedure. If the brake pedal height and firmness results are not achieved, perform the auto bleed procedure below.
ABS Automated Bleed Procedure
- Raise and support the vehicle.
- Remove the tire and wheel assemblies.
- Inspect the battery state of charge.
- Install a scan tool.
- Turn ON the ignition, with the engine OFF.
- With the scan tool, establish communications with the ABS/TCS system. Select Special Functions from the ABS/TCS menu. Select Automated Bleed from the Special Functions menu.
- Bleed the base brake system.
- Follow the scan tool directions until the desired brake pedal height is achieved.
- If the bleed procedure is aborted, a malfunction exists. Perform the following steps before resuming the bleed procedure:
- If a DTC is detected, refer to Diagnostic Trouble Code (DTC) List and diagnose the appropriate DTC.
- If the brake pedal feels spongy, perform the conventional brake bleed procedure again.
- When the desired pedal height is achieved, press the brake pedal in order to inspect for firmness.
- Remove the scan tool.
- Install the tire and wheel assemblies.
- Inspect the brake fluid level.
- Road test the vehicle while inspecting that the pedal remains high and firm.
In most circumstances a base brake bleed is all that is required for most component replacements (such as wheel cylinders, calipers, brake tubes, and master cylinder) except for brake pressure modulator valve (BPMV) replacement.
The following automated antilock brake system (ABS) bleed procedure is required when one of the following occur:
- Manual bleeding at the wheel cylinders does not achieve the desired pedal height or feel.
- Replacement of the BPMV
- Extreme loss of brake fluid has occurred.
- Air ingestion is suspected.
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 a full charge.
- Repair the battery and charging system as necessary.
- Connect a scan tool to the data link connector (DLC) and select the current and history DTCs.
- Repair any DTCs prior to performing the ABS bleed procedure.
- Inspect for visual damage and leaks and repair as needed.
Automated Bleed Procedure
- Before servicing the vehicle refer to the precautions at the beginning of this section.
- Raise and support the vehicle.
- Turn the ignition switch to the OFF position.
- Remove all 4 tires (if necessary)
- Connect the pressure bleeding tool.
- Turn the ignition switch to RUN position with the engine off.
- Connect a scan tool and establish communications with the ABS system.
- Pressurize the bleeding tool to 30-35 psi (206-241 kPa).
The 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 set to 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.
NOTE: 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 1 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, if necessary.
- Remove the pressure from the pressure bleeding tool
- Disconnect the tool from the vehicle.
- Depress the brake pedal to gauge pedal height and feel.
- Repeat the procedure until the pedal is acceptable.
- Remove the scan tool from the DLC connector.
- Safely lower the vehicle.
- Inspect the brake fluid level in master cylinder.
- Road test the vehicle while ensuring 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 TCS solenoids valves. This bleed procedure is the same as above.