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Step
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Action
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Yes
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No
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DEFINITION: This diagnostic table is designed to diagnose ONLY the components of the HYDRAULIC brake system in order to determine if the Hydraulic brake system is operating properly. You will be directed by the appropriate Symptom Table to go to other brake system diagnostic tables as appropriate.
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1
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Were you sent here from a Brake Symptom Table?
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Go to
Step 2
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Go to
Diagnostic Starting Point - Vehicle
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2
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Inspect and adjust the brake fluid level in the brake master cylinder. Refer to
Master Cylinder Reservoir Filling
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Was the brake fluid level low?
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Go to
Step 3
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Go to
Step 4
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3
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1.
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Inspect the brake fluid for the following conditions, indicating brake fluid contamination:
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Fluid separation, indicating two types of fluid are present
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Swirled appearance-oil-based substance
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Layered appearance-silicone-based substance
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Cloudy appearance-moisture
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Dark appearance/suspended particles in fluid-dirt, rust, corrosion, brake dust
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2.
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Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating fluid contamination.
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Do any of the above conditions exist?
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Go to
Step 5
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Go to
Step 6
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4
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1.
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Inspect the brake fluid for the following conditions, indicating brake fluid contamination:
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Fluid separation, indicating two types of fluid are present
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Swirled appearance-oil-based substance
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Layered appearance-silicone-based substance
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Cloudy appearance-moisture
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Dark appearance/ suspended particles in fluid-dirt, rust, corrosion, brake dust
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2.
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Inspect the master cylinder reservoir cap diaphragm and the reservoir-to-master cylinder grommets for swelling, indicating fluid contamination.
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Do any of the above conditions exist?
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Go to
Step 5
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Go to
Step 12
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5
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2.
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If the brake fluid WAS contaminated with an oil-based or a silicone-based fluid, indicated by fluid separation and/or a swollen master cylinder reservoir cap diaphragm and/or swollen reservoir-to-master cylinder grommets, perform the following steps. Refer to the procedures indicated.
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Remove ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
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Clean out the hydraulic brake pipes using denatured alcohol, or equivalent.
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Dry the brake pipes using non-lubricated, filtered air.
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Repair or replace ALL of the following components listed. Each component contains internal rubber seals/linings which have been contaminated.
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Brake master cylinder reservoir: Clean the brake master cylinder reservoir using denatured alcohol, or equivalent, then dry the reservoir using non-lubricated, filtered air, or if necessary, replace the brake master cylinder reservoir.
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Replace the brake master cylinder reservoir cap diaphragm.
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3.
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If the brake fluid was NOT contaminated with an oil-based fluid, but WAS contaminated with water or dirt, rust, corrosion, and/or brake dust, replace the brake master cylinder reservoir cap diaphragm which may have allowed moisture or dirt to enter the system.
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Did you complete the operation and any required repairs and/or replacements?
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Go to
Step 9
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6
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1.
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Inspect the following hydraulic brake system components for external fluid leaks; repair or replace any of the components found to be leaking brake fluid. Refer to the appropriate procedures:
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Brake master cylinder reservoir cap diaphragm
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The presence of air in the system at a bleeder valve location other than at the repair location, except if the brake master cylinder was replaced
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An unrestricted and even flow of brake fluid per axle during the bleeding procedure
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Did you find and correct a condition?
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Go to
Step 7
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Go to
Step 12
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7
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Was there air in the system at a bleeder valve location other than at the repair location, except if the brake master cylinder was replaced?
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Go to
Step 19
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Go to
Step 8
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8
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Was the flow of brake fluid unrestricted and even per axle during the bleeding procedure?
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Go to
Step 9
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Go to
Step 10
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9
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Inspect the hydraulic function of the brake calipers for proper operation. Refer to
Hydraulic Brake Component Operation Visual Inspection
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Was the hydraulic function of the brake calipers operating properly?
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Go to
Step 21
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Go to
Step 14
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10
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Was the flow of brake fluid restricted or uneven through front axle hydraulic components during the bleeding procedure?
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Go to
Step 13
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Go to
Step 11
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11
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Was the flow of brake fluid restricted or uneven through rear axle hydraulic components during the bleeding procedure?
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Go to
Step 17
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12
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Inspect the hydraulic function of the brake calipers for proper operation. Refer to
Hydraulic Brake Component Operation Visual Inspection
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Was the hydraulic function of the brake calipers operating properly?
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Go to
Step 15
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Go to
Step 13
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13
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Determine if the brake caliper is restricting the flow of brake fluid and/or not operating properly:
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3.
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Open the suspected caliper bleeder valve.
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4.
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Using a large C-clamp, compress the caliper piston and observe for an unrestricted flow of brake fluid and for free movement of the caliper piston.
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5.
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Close the caliper bleeder valve.
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Was the flow of brake fluid unrestricted and did the caliper piston move freely?
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Go to
Step 17
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Go to
Step 14
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14
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Repair or replace any brake caliper that was not operating properly. Refer to the appropriate procedure:
Did you complete the repair and/or replacement?
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Go to
Step 21
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15
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Bleed the hydraulic brake system to observe for the presence of air in the system and to observe for an unrestricted and even flow of brake fluid per axle during the bleeding procedure. Refer to
Hydraulic Brake System Bleeding (Manual)
Hydraulic Brake System Bleeding (Pressure)
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Was there air in the system?
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Go to
Step 19
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Go to
Step 16
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16
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Was the flow of brake fluid unrestricted and even per axle during the bleeding procedure?
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Go to
Step 21
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Go to
Step 17
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17
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1.
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Inspect the hydraulic brake pipes and flexible brake hoses for signs of a fluid restriction; such as being bent, kinked, pinched or damaged. Refer to
Brake Pipe and Hose Inspection
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2.
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Replace any of the hydraulic brake pipes and/or flexible brake hoses found to be bent, kinked, pinched or damaged. Refer to the following procedures as necessary:
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3.
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If none of the hydraulic brake pipes or flexible brake hoses were visibly bent, kinked, pinched or damaged, replace the hydraulic brake flex hose at the restricted location.
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Did you find and correct a condition?
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Go to
Step 21
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Go to
Step 18
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18
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Replace the brake pressure modulator valve (BPMV), in order to correct the hydraulic brake dynamic rear proportioning mechanical operation. Refer to
Brake Pressure Modulator Valve Replacement
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Did you complete the replacement?
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Go to
Step 21
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19
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1.
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Inspect the hydraulic brake system components for brake fluid seepage at a seal and/or fitting location, which may have drawn air into the system.
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2.
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Inspect the hydraulic brake system components for evidence of a recent repair, which may have introduced air into the system.
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3.
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Repair or replace any of the components found to be installed incorrectly or seeping brake fluid.
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Did you find and correct a condition?
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Go to
Step 21
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Go to
Step 20
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20
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Did you find and correct a condition?
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Go to
Step 21
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Return to Symptom Table
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21
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Install or connect components that were removed or disconnected during diagnosis.
Did you complete the operation?
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Hydraulic Brake System OK
Return to Symptom Table
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