System Component Description
The brake assist system consists of the following
System Operation
Brake system input force from the driver is multiplied by the brake pedal and transferred by the pedal pushrod to the hydraulic brake master cylinder. Effort required to apply the brake system is reduced by the operation of the vacuum brake booster.
When brake system force is applied, vacuum to the rear of the diaphragm(s) is cut off, and air at atmospheric pressure is admitted in its place. The vacuum acts to pull the diaphragm (s) forward, while the atmospheric pressure acts to push from behind. As a result, the amount of effort required by the driver is reduced. When input force is removed, vacuum again replaces atmospheric pressure within the vacuum power brake booster to help return the booster to rest. Return springs maintain the system in a rest position.
If the vehicle is equipped with a vacuum monitoring system, the powertrain control module (s) typically will alter powertrain functions and/or command the vacuum pump ON, if equipped, to provide for the vacuum needs of the brake assist system, as operating conditions warrant.
The hydraulic brake system consists of the following
Mechanical force is converted into hydraulic pressure by the master cylinder, regulated to meet braking system demands by the pressure balance control system, and delivered to the hydraulic brake wheel circuits by the pipes and flexible hoses. The wheel apply components then convert the hydraulic pressure back into mechanical force which presses linings against rotating brake system components.
| DTC | Description |
|---|---|
| DTC C0267 | Low Brake Fluid Indicated |
| DTC C027B | Brake Booster Electric Vacuum Pump Malfunction |
| DTC C0299 | Brake Booster Large Vacuum Leak Detected Not Plausible |
| DTC C1100 | Brake Pressure Sensor 2 |
Footbrake System DTC Index
Circuit/System Description
The instrument cluster turns ON the brake warning indicator for 5 seconds after ignition ON as a test of the indicator warning lamps. When the fluid within the brake fluid reservoir is low, contacts within the sensor closes causing the voltage within the sensor signal circuit to drop. The electronic brake control module (EBCM) will detect the voltage drop and will send a serial data message to the instrument cluster commanding the brake warning indicator to illuminate.
Description and Operation
HYDRAULIC BRAKE SYSTEM DESCRIPTION AND OPERATION
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic brake control module (EBCM) supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal to the EBCM that is proportional to the pressure in the brake booster. When the vacuum within the system drops, the EBCM turns ON the vacuum pump by providing ground to the vacuum pump relay. The relay activates and supplies voltage to the brake booster pump motor.
BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic brake control module (EBCM) supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to the EBCM.
BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION
The brake booster vacuum sensor measures the vacuum in the brake booster assembly. The electronic brake control module (EBCM) supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to the EBCM.
BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION
The electronic brake control module (EBCM) monitors the control circuit of the brake booster pump relay. The EBCM supplies ground through the pump relay control circuit which then supplies B+ voltage to actuate the brake booster pump. B+ voltage is supplied at all times to the coil side of the pump relay.
BRAKE ASSIST SYSTEM DESCRIPTION AND OPERATION
Electronic brake control module (EBCM) monitors the brake fluid level in the brake fluid reservoir. When the fluid within the brake fluid reservoir is below the MIN level, contacts within the brake fluid level switch closes causing the voltage within the signal circuit to drop. The EBCM will detect the voltage drop and will send a serial data message to the instrument cluster commanding the brake warning indicator to illuminate.
HYDRAULIC BRAKE SYSTEM DESCRIPTION AND OPERATION
Test Description
The numbers below refer to the step numbers on the diagnostic table.
4
Suspension components that are not operating properly may cause a disturbance to the vehicle during application of the brake system.
5
Steering components that are not operating properly may cause a disturbance to the vehicle during application of the brake system.
| Step | Action | Yes | No |
|---|---|---|---|
| DEFINITION: Vehicle pulls to one side only when braking. | |||
| 1 | Were you sent here from the Hydraulic Brake Symptom table? | Go to Step 2 | Go to DIAGNOSTIC STARTING POINT - VEHICLE |
| 2 | Inspect the hydraulic brake system for the following conditions. Kinked, pinched or damaged brake pipe or flexible brake hose Sticking or improperly operating caliper piston Brake fluid leak Adjust, repair or replace components as necessary. Refer to HYDRAULIC BRAKE SYSTEM DIAGNOSIS . Did you find and correct a condition? | Go to Step 6 | Go to Step 3 |
| 3 | Inspect the disc brake system for the following conditions. Contaminated linings Glazed linings Distorted, cracked or damaged linings on one side Loose, damaged or missing caliper hardware and/or lining hardware Incorrect linings on one side Hard spots, heat checks, blueing discoloration of rotor friction surfaces; possibly due to brake drag Glazed rotor friction surfaces Bent or damaged caliper or mounting component Adjust, repair or replace components as necessary. Refer to DISC BRAKE SYSTEM DIAGNOSIS . Did you find and correct a condition? | Go to Step 6 | Go to Step 4 |
| 4 | Inspect the suspension system for the following conditions. Incorrect tire pressures Loose suspension component connections Excessively worn or damaged suspension components Adjust, repair or replace components as necessary. Refer to DIAGNOSTIC STARTING POINT - VEHICLE . Did you find and correct a condition? | Go to Step 6 | Go to Step 5 |
| 5 | Inspect the steering system for the following conditions. Loose steering component connections Excessively worn or damaged steering components Adjust, repair or replace components as necessary. Refer to DIAGNOSTIC STARTING POINT - VEHICLE . Did you find and correct a condition? | Go to Step 6 | Go to DIAGNOSTIC STARTING POINT - VEHICLE |
| 6 | Install or connect components that were removed or disconnected during diagnosis. Road test the vehicle in order to confirm proper operation. Refer to BRAKE SYSTEM VEHICLE ROAD TEST . Is the condition still present? | Go to Step 2 | System OK |
Test Descriptions
The number below refers to the step number on the diagnostic table.
4
Suspension components that are not operating properly may cause a disturbance to the vehicle during application of the brake system.
| Step | Action | Yes | No |
|---|---|---|---|
| DEFINITION: Braking action or stopping force sensitive or grabbing and/or more pronounced at the front or at the rear axle. Sensitive or grabbing brakes: Excessive brake jump-in force relative to brake pedal input. | |||
| 1 | Were you sent here from the Hydraulic Brake Symptom table? | Go to Step 2 | Go to DIAGNOSTIC STARTING POINT - VEHICLE |
| 2 | Inspect the hydraulic brake system for the following conditions: Improper operation of caliper pistons Kinked, pinched or damaged brake pipe or flexible brake hose Brake fluid leak Improperly functioning proportion valve, if equipped Improper operation of dynamic rear proportion (DRP) system, if equipped Adjust, repair or replace components as necessary. Refer to HYDRAULIC BRAKE SYSTEM DIAGNOSIS . Did you find and correct a condition? | Go to Step 6 | Go to Step 3 |
| 3 | Inspect the disc brake system for the following conditions: Contaminated linings Glazed linings Distorted, cracked or damaged linings Excessively worn linings Aftermarket linings Damaged or excessively worn caliper hardware and/or lining hardware Hard spots, heat checks, blueing discoloration of rotor friction surfaces Glazed rotor friction surfaces Adjust, repair or replace components as necessary. Refer to DISC BRAKE SYSTEM DIAGNOSIS . Did you find and correct a condition? | Go to Step 6 | Go to Step 4 |
| 4 | Inspect the suspension system for the following conditions: Loose suspension component connections Excessively worn or damaged suspension components Adjust, repair or replace components as necessary. Refer to DIAGNOSTIC STARTING POINT - VEHICLE . Did you find and correct a condition? | Go to Step 6 | Go to Step 5 |
| 5 | Inspect the brake assist system for the following conditions: Binding, bent or damaged pedal pushrod, pedal, or pedal bracket Damaged or improperly operating vacuum booster, if equipped Damaged or improperly operating hydraulic booster, if equipped Adjust, repair or replace components as necessary. Refer to BRAKE ASSIST SYSTEM DIAGNOSIS . Did you find and correct a condition? | Go to Step 6 | Go to DIAGNOSTIC STARTING POINT - VEHICLE |
| 6 | Install or connect components that were removed or disconnected during diagnosis. Road test the vehicle in order to confirm proper operation. Refer to BRAKE SYSTEM VEHICLE ROAD TEST . Is the condition still present? | Go to Step 2 | System OK |
The numbers below refer to the step numbers on the diagnostic table
9 Lubricant leaks from non-brake system components may come in contact with and contaminate brake system components.
10 Lubricant leaks from non-brake system components may come in contact with and contaminate brake system components.
12 Disc brake rotor shields/backing plates that come in contact with disc brake rotors may cause brake system noise.
15 Disc brake rotor thickness variation that exceeds the maximum acceptable level can cause brake pulsation.
19 Disc brake rotor thickness variation that exceeds the maximum acceptable level can cause brake pulsation.
22 Disc brake rotor assembled lateral runout (LRO) that exceeds the maximum acceptable level can lead to thickness variation.
| Step | Action | Yes | No |
|---|---|---|---|
| DEFINITION: This diagnostic table is designed to diagnose ONLY the components of the DISC brake system in order to determine if the DISC brake 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 2 | Go to DIAGNOSTIC STARTING POINT - VEHICLE |
| 2 | Visually inspect the disc brake pads for the following conditions: Refer to FRONT DISC BRAKE PADS REPLACEMENT and/or REAR DISC BRAKE PADS REPLACEMENT . Lining thickness below specifications Uneven and/or abnormal wear-edge-to-edge and/or side-to-side Looseness or damage-including pad hardware Evidence of contamination from an external substance Did you find any conditions to indicate a concern with any of the front and/or rear disc brake pads? | Go to Step 3 | Go to Step 12 |
| 3 | Are any of the front and/or rear disc brake pads contaminated? | Go to Step 8 | Go to Step 4 |
| 4 | Are any of the front and/or rear disc brake pads worn unevenly? | Go to Step 7 | Go to Step 5 |
| 5 | Are any of the front and/or rear disc brake pads and/or pad hardware loose or damaged? | Go to Step 7 | Go to Step 6 |
| 6 | Remove and inspect the worn disc brake pads for glazing, looseness, heat spots or damage. Replace the worn disc brake pads as a complete axle set. Refer to FRONT DISC BRAKE PADS REPLACEMENT and/or REAR DISC BRAKE PADS REPLACEMENT . Did you complete the inspection and replacement? | Go to Step 12 | |
| 7 | WARNING: Support the brake caliper with a strong metal wire, or equivalent. This applies whenever the caliper is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak. NOTE: Do NOT disconnect the hydraulic brake flex hoses from the calipers. Remove the front and/or rear disc brake calipers, as appropriate, from the mounting brackets or from the suspension knuckles and support the calipers. Refer to FRONT BRAKE CALIPER REPLACEMENT and/or REAR BRAKE CALIPER REPLACEMENT . Inspect the disc brake caliper mounting bracket or the suspension knuckles and the mounting/sliding hardware for the following conditions: Refer to FRONT DISC BRAKE MOUNTING AND HARDWARE INSPECTION and/or REAR DISC BRAKE MOUNTING AND HARDWARE INSPECTION . Binding or seized hardware Worn, damaged or missing hardware components Loose, bent, cracked, or damaged caliper mounting bracket or suspension knuckle Replace components as required. Refer to the following procedures, as required: FRONT BRAKE CALIPER BRACKET REPLACEMENT REAR BRAKE CALIPER BRACKET REPLACEMENT FRONT BRAKE CALIPER HARDWARE REPLACEMENT REAR BRAKE CALIPER HARDWARE REPLACEMENT Replace the unevenly-worn, loose or damaged disc brake pads as a complete axle set. Refer to FRONT DISC BRAKE PADS REPLACEMENT and/or REAR DISC BRAKE PADS REPLACEMENT . Did you complete the inspection and replacement? | Go to Step 12 | |
| 8 | Inspect the disc brake calipers, brake hoses and brake pipes for evidence of an external brake fluid leak. Replace any components found to be leaking brake fluid. Refer to the following procedures as required: FRONT BRAKE CALIPER REPLACEMENT REAR BRAKE CALIPER OVERHAUL or REAR BRAKE CALIPER REPLACEMENT FRONT BRAKE HOSE REPLACEMENT REAR BRAKE HOSE REPLACEMENT BRAKE PIPE REPLACEMENT Did you find and correct the source of the leak causing contamination of the pads? | Go to Step 11 | Go to Step 9 |
| 9 | Inspect the wheel drive shaft outer seals for damage and evidence of a grease leak. Replace any wheel drive shaft seal that is found to be leaking grease which may be the source of the contamination to the pads. Refer to FRONT WHEEL DRIVE SHAFT INNER JOINT AND BOOT REPLACEMENT and/or REAR WHEEL DRIVE SHAFT INNER JOINT AND BOOT REPLACEMENT . Did you find and correct the source of the leak causing contamination of the pads? | Go to Step 11 | Go to Step 10 |
| 10 | Inspect the automatic transmission cooling system lines, if equipped, for damage and evidence of an external fluid leak which may be the source of the contamination to the pads. Inspect the power steering system hoses for damage and evidence of an external fluid leak which may be the source of the contamination to the pads. Replace any components found to be leaking fluid which may be the source of the contamination to the pads. Did you find and correct the source of the leak causing contamination of the pads? | Go to Step 11 | |
| 11 | Clean the remaining disc brake system components to remove any traces of the contaminant. WARNING: Support the brake caliper with a strong metal wire, or equivalent. This applies whenever the caliper is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak. NOTE: Do NOT disconnect the hydraulic brake flex hoses from the calipers. Remove the front and/or rear disc brake calipers, as appropriate, from the mounting brackets or the suspension knuckles and support the calipers. Refer to FRONT BRAKE CALIPER REPLACEMENT and/or REAR BRAKE CALIPER REPLACEMENT . Inspect the disc brake caliper mounting/sliding hardware for the following conditions: Refer to FRONT DISC BRAKE MOUNTING AND HARDWARE INSPECTION and/or REAR DISC BRAKE MOUNTING AND HARDWARE INSPECTION . Binding or seized hardware Distorted, worn, damaged or missing hardware components Replace the caliper mounting/sliding hardware components as required. Refer to FRONT BRAKE CALIPER HARDWARE REPLACEMENT and/or REAR BRAKE CALIPER HARDWARE REPLACEMENT . Replace the contaminated disc brake pads as a complete axle set. Refer to FRONT DISC BRAKE PADS REPLACEMENT and/or REAR DISC BRAKE PADS REPLACEMENT . Did you complete the cleaning, inspection and replacement? | Go to Step 12 | |
| 12 | Visually inspect each of the disc brake rotor shields/backing plates, if equipped, for evidence of contact with the brake rotors. Are any of the brake rotor shields/backing plates contacting the brake rotors? | Go to Step 13 | Go to Step 14 |
| 13 | Repair or replace the disc brake rotor shields/backing plates as required. Refer to FRONT BRAKE SHIELD REPLACEMENT . Did you complete the repair or replacement? | Go to Step 14 | |
| 14 | Check the thickness of each of the disc brake rotors. NOTE: Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. Make a determination for each brake rotor if the rotor can be REFINISHED and REMAIN ABOVE the minimum requirements. Refer to BRAKE ROTOR THICKNESS MEASUREMENT . Does the disc brake rotor meet the minimum requirements for REFINISHING? | Go to Step 15 | Go to Step 18 |
| 15 | NOTE: Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. Inspect each of the disc brake rotors for thickness variation that exceeds the maximum acceptable level. Refer to BRAKE ROTOR THICKNESS VARIATION MEASUREMENT . Does the brake rotor exhibit thickness variation that exceeds the maximum acceptable level? | Go to Step 17 | Go to Step 16 |
| 16 | Inspect each of the disc brake rotors for the following surface and wear conditions: Refer to BRAKE ROTOR SURFACE AND WEAR INSPECTION . Heavy rust and/or pitting Cracks and/or heat spots Excessive blueing discoloration Deep or excessive scoring beyond maximum acceptable level NOTE: Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. Make a determination for each brake rotor if the rotor requires refinishing based upon the results of the inspection. If the brake rotor exhibits any of the conditions listed previously, it requires refinishing. Does the brake rotor require REFINISHING? | Go to Step 17 | Go to Step 22 |
| 17 | Refinish the brake rotor. Refer to BRAKE ROTOR REFINISHING . Inspect the brake rotor thickness. Refer to BRAKE ROTOR THICKNESS MEASUREMENT . Were you able to REFINISH the brake rotor within the minimum requirements? | Go to Step 22 | Go to Step 21 |
| 18 | Is the brake rotor at or below the MINIMUM THICKNESS requirements? | Go to Step 21 | Go to Step 19 |
| 19 | NOTE: Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. Inspect each of the disc brake rotors for thickness variation that exceeds the maximum acceptable level. Refer to BRAKE ROTOR THICKNESS VARIATION MEASUREMENT . Does the brake rotor exhibit thickness variation that exceeds the maximum acceptable level? | Go to Step 21 | Go to Step 20 |
| 20 | Inspect each of the disc brake rotors for the following surface and wear conditions: Refer to BRAKE ROTOR SURFACE AND WEAR INSPECTION . Heavy rust and/or pitting Cracks and/or heat spots Excessive blueing discoloration Deep or excessive scoring beyond maximum acceptable level NOTE: Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. Make a determination for each brake rotor if the rotor requires replacement based upon the results of the inspection. If the brake rotor exhibits any of the conditions listed previously, it requires replacement. Does the brake rotor require REPLACEMENT? | Go to Step 21 | Go to Step 22 |
| 21 | NOTE: Whenever a brake rotor is replaced, the assembled lateral runout (LRO) of the rotor must be measured to ensure optimum performance of the disc brakes. Replace the brake rotor. Refer to FRONT BRAKE ROTOR REPLACEMENT or REAR BRAKE ROTOR REPLACEMENT .Did you complete the replacement? | Go to Step 24 | |
| 22 | NOTE: Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. Inspect each of the disc brake rotors for assembled lateral runout (LRO) that exceeds the maximum acceptable level. Refer to BRAKE ROTOR ASSEMBLED LATERAL RUNOUT MEASUREMENT .Does the brake rotor exhibit assembled LRO that exceeds the maximum acceptable level? | Go to Step 23 | Go to Step 24 |
| 23 | Correct the LRO for each brake rotor that was determined to have LRO exceeding the maximum acceptable level. Refer to BRAKE ROTOR ASSEMBLED LATERAL RUNOUT CORRECTION . Did you complete the operation? | Go to Step 24 | |
| 24 | Install or connect components that were removed or disconnected during diagnosis. Did you complete the operation? | Disc Brake System OK Return to Symptom Table | |
| WARNING |
|---|
| Support the brake caliper with a strong metal wire, or equivalent. This applies whenever the caliper is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak. |
| NOTE |
|---|
| Do NOT disconnect the hydraulic brake flex hoses from the calipers. |
| WARNING |
|---|
| Support the brake caliper with a strong metal wire, or equivalent. This applies whenever the caliper is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak. |
| NOTE |
|---|
| Do NOT disconnect the hydraulic brake flex hoses from the calipers. |
| NOTE |
|---|
| Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. |
| NOTE |
|---|
| Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. |
| NOTE |
|---|
| Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. |
| NOTE |
|---|
| Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. |
| NOTE |
|---|
| Make the following determination AND ANSWER the question INDIVIDUALLY for EACH rotor. |
| NOTE |
|---|
| Whenever a brake rotor is replaced, the assembled lateral runout (LRO) of the rotor must be measured to ensure optimum performance of the disc brakes. |
| NOTE |
|---|
| Perform the following inspection AND ANSWER the question INDIVIDUALLY for EACH rotor. |