The master cylinder reservoirs must be kept properly filled to prevent air from entering the system. No special filling procedures are required because of the anti-lock system.
When adding fluid, use only DOT 3 fluid; the use of DOT 5 or silicone fluids is specifically prohibited. Use of improper or contaminated fluid may cause the fluid to boil or cause the rubber components in the system to deteriorate. Never use any fluid with a petroleum base or any fluid which has been exposed to water or moisture.
Auto Bleed Procedure
The auto-bleed procedure is used to provide a complete brake system bleed on vehicles with ABS. The procedure cycles the system valves and runs the pump to purge air from secondary circuits normally closed off during non-ABS/TCS mode operation and bleeding. It is to be used when it is suspected that air has been ingested into the systems secondary circuits, or when the BPMV has been replaced.
To successfully perform this procedure, you will need the following equipment:
- Scan tool
- Pressure brake bleeder that can produce at least 30 psi
- Jack and stands to safely support the vehicle.
- Clean plastic bleeder bottle with a hose that fits snugly on the bleeder valves. The other end of the hose should protrude into the bottle, with its end immersed in brake fluid.
- Assistant to pump the brake pedal during the procedure.
- Suitable safety apparel, including goggles.
- Raise and safely support the vehicle.
- Remove all 4 wheel and tire assemblies.
- Check the brake system for leaks and/or component damage. If any if found, they must be fixed before performing the procedure.
- Make sure the vehicle's battery is in a full state of charge.
- Connect a Tech 1® or equivalent scan tool to the DLC.
- Turn the ignition to the RUN position, but do NOT start the engine.
- Establish communications with the scan tool and select ABS/TCS features.
- Select "Special Tests".
- Select "Automated Bleed Procedure".
- Bleed the base brakes as outlined earlier in this section.
- Follow the scan tool menu driven instructions until the proper brake pedal height is achieved. If any malfunctions are found, the bleed procedure will be aborted. If DTCs are present, the scan tool will display "DTCs PRESENT" or list the DTCs depending on when the DTCs were set. The DTCs can be displayed or cleared as appropriate in the "Trouble Codes" mode. Refer to the code list earlier in this section for ABS codes. If the test is aborted, but no codes are found, check and correct all system malfunctions before attempting the bleed procedure again. If a road test is necessary for diagnosis, and the brake pedal feels spongy, perform a conventional brake bleed, making sure to achieve a firm brake pedal before driving the vehicle.
- When the Auto Bleed Procedure is complete, depress the brake pedal. It should be high and firm. If not, re-inspect the brake system thoroughly for any conditions which could cause excess brake pedal travel. If the brake system is OK, but the excessive brake pedal travel exists, repeat the Auto Bleed Procedure.
- Disconnect the scan tool. Reinstall the wheel and tire assemblies, then carefully lower the vehicle. Check the fluid level in the reservoir and add if necessary. Road test the vehicle, making several ABS and Traction Control actuations in a suitable area. The brake pedal should stay high and firm after the road test.