Bleeding brakes, especially in vehicles equipped with Anti-lock Braking Systems (ABS), can sometimes require more than just the traditional pump-and-hold method. When air gets trapped in the ABS Hydraulic Control Unit (HCU), a specialized tool like a DRB scan tool becomes essential. This guide will walk you through the process of effectively bleeding your brakes using a DRB scan tool, ensuring a firm pedal and optimal braking performance.
Before starting, it’s important to understand why a DRB scan tool is necessary for certain ABS brake bleeding procedures. Conventional bleeding methods may not always remove air trapped within the ABS pump and solenoids. The DRB scan tool, or equivalent professional diagnostic tool, can cycle the ABS pump and valves, forcing trapped air out of the HCU and into the brake lines where it can be bled in a controlled manner.
Step-by-Step Brake Bleeding Procedure with DRB Scan Tool
This procedure combines conventional brake bleeding techniques with the use of the DRB scan tool to ensure all air is purged from the brake system.
1. Prepare the Master Cylinder
If you are replacing the master cylinder, it’s crucial to bench bleed it before installation. This pre-bleeding step eliminates air from the master cylinder itself, simplifying the bleeding process once installed in the vehicle.
Alt text: Brake caliper bleed screw with hose submerged in brake fluid container for bleeding process.
Regardless of whether you’re replacing the master cylinder, begin by cleaning the master cylinder reservoir and cap to prevent contaminants from entering the brake fluid. Open the reservoir and fill it with fresh, high-quality Mopar brake fluid or equivalent DOT 3 or DOT 4 fluid as specified for your vehicle.
2. Initial Conventional Brake Bleeding
Perform a preliminary conventional brake bleed to remove the majority of air from the brake lines and components before engaging the DRB scan tool.
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Master Cylinder and Combination Valve Bleeding: Locate the brake line fittings at the master cylinder and combination valve (if applicable). With the help of an assistant, have them depress and release the brake pedal while you slightly loosen and then tighten these fittings to bleed out any air.
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Wheel Brake Bleeding Sequence: Bleed the wheel brakes in the correct sequence, starting with the wheel furthest from the master cylinder and moving progressively closer. The typical sequence is:
- Right Rear
- Left Rear
- Right Front
- Left Front
Alt text: Close-up of glass container with brake fluid and submerged hose during brake bleeding, showing air bubbles.
- Bleeding Procedure at Each Wheel:
- Attach a bleed hose to the brake caliper bleed screw of the wheel you are bleeding. Submerge the other end of the hose in a clear container partially filled with brake fluid. Ensure the hose end remains submerged to prevent air from being drawn back into the system.
- Instruct your assistant to slowly depress and hold the brake pedal to the floor.
- Open the bleed screw approximately ½ turn. Observe the brake fluid flowing into the container, along with any air bubbles. Close the bleed screw just as the brake pedal reaches the floor. Important: Do not pump the brake pedal during this process, as it can create small air bubbles that are harder to remove.
- Repeat this bleeding operation at each wheel until the brake fluid entering the container is completely free of air bubbles. Regularly check and replenish the brake fluid level in the master cylinder reservoir throughout this process to prevent it from running dry, which could introduce more air into the system.
3. HCU Bleeding with DRB Scan Tool
This is the critical step where the DRB scan tool is used to cycle the ABS HCU and bleed any trapped air within it.
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Connect the DRB Scan Tool: Locate the ABS diagnostic connector in your vehicle. In many models, this connector is found under the carpet at the front of the console, near the instrument panel center bezel. Connect your DRB scan tool to this connector.
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Initiate ABS Bleed Function: Navigate the scan tool menu to access the ABS bleed function. Typically, this involves selecting “CHASSIS SYSTEM,” then “TEVES ABS BRAKES,” and finally “BLEED BRAKES.” Follow the on-screen prompts provided by the DRB scan tool to initiate the HCU bleeding process. The scan tool will cycle the ABS pump and solenoids, effectively bleeding the HCU.
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Complete Scan Tool Test: Allow the DRB scan tool to complete the bleeding cycle. The scan tool will usually display a “TEST COMPLETE” message once the HCU bleed procedure is finished. Once complete, disconnect the DRB scan tool.
4. Final Conventional Brake Bleeding
After using the DRB scan tool to bleed the HCU, it is necessary to perform a second conventional brake bleed. This step removes any air that may have been pushed into the brake lines during the HCU bleeding process.
- Repeat the conventional bleeding procedure outlined in Step 2, starting again with bleeding the master cylinder/combination valve fittings and then proceeding through the wheel brake bleeding sequence (Right Rear, Left Rear, Right Front, Left Front). Bleed each wheel until bubble-free fluid is observed.
5. Final Checks and Verification
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Top Off Brake Fluid: Ensure the brake fluid in the master cylinder reservoir is filled to the correct level.
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Brake Pedal Feel and Operation: Carefully check the brake pedal feel. It should be firm and responsive. Pump the brakes several times to confirm proper operation.
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Road Test (Carefully): Before driving in normal traffic, perform a careful low-speed test in a safe environment to verify proper brake function and ensure the ABS system is operating correctly.
By following these steps and utilizing a DRB scan tool, you can effectively bleed brakes on vehicles with ABS, ensuring optimal braking performance and safety. Remember to always use the correct type of brake fluid and consult your vehicle’s service manual for any specific instructions or recommendations.
