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Brake Assist System Diagnosis

WARNING: This page is about a different car, the 2007 Suzuki XL7. However, it is still accessible from the selected car via links, so may be relevant.
DIAGNOSIS PROCEDURE TABLE - BRAKE ASSIST SYSTEM DIAGNOSIS

Step Action Yes No
DEFINITION: This diagnostic table is designed to diagnose ONLY the components of the brake ASSIST system in order to determine if the brake ASSIST system is operating properly. You will be directed by the appropriate Symptom table to go to other brake system diagnostic tables as appropriate.
1 Were you sent here from a Brake Symptom table? Go to Step 3 Go to Step 2
2 Were you sent here directly from an electrical diagnostic to investigate vacuum as a possible concern? Go to Step 5 Go to DIAGNOSTIC STARTING POINT - HYDRAULIC BRAKES 
3 Inspect for proper brake pedal travel. Refer to BRAKE PEDAL TRAVEL MEASUREMENT AND INSPECTION .
Is the brake pedal travel distance within the acceptable limits?		 Go to Step 5 Go to Step 4
4
  1. Inspect for worn, missing, misaligned, bent, or damaged brake pedal system components.
    • For the brake pedal pushrod component inspection, refer to BRAKE PEDAL PUSHROD INSPECTION .
    • Inspect the brake pedal bushings for excessive wear and/or damage and inspect the brake pedal for a misaligned, bent, and/or damaged condition.
  2. Replace the brake pedal system components that are worn, missing, misaligned, bent, or damaged.

Did you find and replace any worn, missing, misaligned, bent, or damaged brake pedal system components?		 Go to Step 5 Inspect for internal and external fluid leaks and air in the hydraulic brake system Go to HYDRAULIC BRAKE SYSTEM DIAGNOSIS 
5 Check the engine vacuum source that supplies vacuum to the vacuum brake booster. Refer to BRAKE SYSTEM VACUUM SOURCE TEST .
Is the vacuum reading within the acceptable limits?		 Go to Step 6 Go to Engine Controls Diagnostics Information
6 Does the condition occur during cold start-up conditions? Go to Step 7 Go to Step 8
7 Check engine vacuum under the same cold start-up conditions.
Refer to Engine Controls Diagnostics.
Did you find and correct a condition?		 Go to Step 18 Go to Step 9
8 During the vacuum source test, did the vacuum booster check valve operate properly? Go to Step 10 Go to Step 9
9 Replace the vacuum booster check valve. Refer to VACUUM BRAKE BOOSTER CHECK VALVE AND/OR HOSE REPLACEMENT . Did you complete the replacement? Go to Step 10 -
10 If equipped with a booster mounted separate vacuum sensor, inspect the vacuum sensor grommet for cracks, cuts, dry-rot, or damage.
Does the vacuum sensor grommet exhibit any of the conditions listed?		 Go to Step 11 Go to Step 12
11 Replace the vacuum sensor grommet.
Did you complete the replacement?		 Go to Step 12 -
12
  1. Separate the master cylinder from the vacuum brake booster. Do not disconnect any brake pipes. Before removing the master cylinder, first deplete the vacuum by removing the check valve or applying the brake pedal several times. Refer to REMOVAL PROCEDURE .
  2. If equipped with a vacuum seal on the rear of the master cylinder, inspect the seal for damage and correct positioning on the master cylinder.
  3. If equipped with a vacuum seal that is part of the booster, inspect the seal for damage.
  4. Inspect the master cylinder mating surface of the booster form deformation and or damage.

Does the vacuum seal and/or the master cylinder mating surface of the of the booster exhibit any of the conditions listed?		 Go to Step 13 Go to Step 14
13
  1. If equipped with a vacuum seal on the rear of the master cylinder, replace the vacuum seal as necessary.
  2. If equipped with a vacuum seal that requires replacement and which is part of the booster, the booster assembly must be replaced.
  3. If the master cylinder mating surface of the booster was deformed and/or damaged, replace the booster.

Did you complete the replacement?		 Go to Step 14 -
14 Perform the vacuum boost functional test:
  1. Reinstall the master cylinder to the booster.
  2. If the engine was started after reinstalling the master cylinder to the booster, perform the following: With the engine OFF, depress the brake pedal several times to deplete the vacuum reserve.
  3. Depress and maintain moderate foot pressure on the brake pedal.
    NOTE: The brake pedal should fall slightly, then hold.
  4. Start the engine and observe pedal operation.

Is there an audible vacuum leak coming from the brake pedal area?		 Go to Step 17 Go to Step 15
15 Did the brake pedal fall slightly after the engine was started, then hold? Go to Step 16 Go to Step 17
16 Perform the vacuum booster leak-down test:
  1. Release the brake pedal.
  2. Accelerate the engine to approximately 3,000 RPM, then release the throttle. Wait 2-3 seconds and repeat once.
  3. Turn the ignition OFF.
  4. Wait 60 seconds.
    NOTE:
    • Both pedal applies should be assisted.
    • The amount of assist could diminish slightly with the second apply.
  5. Depress the brake pedal 2 times to check for vacuum booster available vacuum reserve. Observe pedal effort.

Were both pedal applies power assisted?		 Go to Step 18 Go to Step 17
17 Replace the vacuum brake booster. Refer to VACUUM BRAKE BOOSTER REPLACEMENT .
Did you complete the replacement?		 Go to Step 18 -
18 Install or connect any components that were removed or disconnected during diagnosis.
Did you complete the operation?		 Brake Assist System OK Return to Symptom Table -
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