| Diagnosis and Testing This procedure is for the diagnosis and testing of the mechanical EBA. For the diagnosis and testing procedure for vehicles equipped with electronic EBA, REFER to Section 206-09A Anti-Lock Control / 206-09B Anti-Lock Control - Traction Control / 206-09C Anti-Lock Control - Stability Assist. Principles of Operation All critical braking situations are immediately detected by the hydraulic mechanism incorporated in the brake master cylinder that is sensitive to the effect and speed of application of the brake pedal. When activated, this has an immediate affect on the pressure distribution in the brake master cylinder and allows for the generation of high pressure braking levels with a reduced brake pedal effort. The brake system pressure is modulated by slightly releasing the brake pedal. When the brake pedal pressure is reduced below its threshold value, the EBA system is deactivated. Inspection and Verification - Verify the customer concern.
- Visually inspect for obvious signs of mechanical damage.
Visual Inspection Chart | Mechanical | - Tire pressures
- Wheels and tires
- Brake line damage
- Fluid leaks
- Fluid level
- Fluid contamination
| - If an obvious cause for an observed or reported concern is found, correct the cause (if possible) before proceeding to the next step.
- If the concern is not visually evident, verify the symptom and refer to the Symptom Chart.
Symptom Chart | Symptom | Possible Sources | Action | | The emergency brake assist (EBA) is inoperative | * Brake assist valve. | * CARRY OUT the emergency brake assist (EBA) function tests in this section. | Function Tests Static Diagnosis To simulate normal braking: - Run the engine for 30 seconds.
- Depress the brake pedal slowly with maximum pedal effort to just beyond the pressure point and hold.
- Hold the brake pedal in this position for a minimum of 10 seconds.
- Release the brake pedal by half of the pedal travel and pulsate the pedal.
- If the resistance in the brake pedal is low (the pedal feels soft), then the system has switched to EBA mode and is operating correctly. This condition is considered normal and does not indicate that the brake master cylinder is in need of renewal.
Dynamic Diagnosis To simulate an emergency braking situation: - Carry out a road test at a speed of 40-50 km/h (25-30 mph).
- Simulate an emergency braking situation using a high pedal application speed (wait at least 30 seconds before repeating the test).
- The anti-lock brake system (ABS) will be activated with the aid of the EBA.
- The brake pedal can modulate the brake system pressure.
- If the resistance in the brake pedal is low (the pedal feels soft), then the system has switched to EBA mode and is operating correctly. This condition is considered normal and does not indicate that the brake master cylinder is in need of renewal.
If only the static diagnosis was successful, then the brake pedal was not depressed rapidly enough during the dynamic diagnosis. If both the static and dynamic diagnosis were unsuccessful, check that the brake booster is operating correctly before installing a new EBA brake master cylinder. REFER to Section 206-06 Hydraulic Brake Actuation. | 
