* ABS Warning Light: This is the most obvious sign. If the ABS warning light is illuminated on your dashboard, it means the system has detected a malfunction. This doesn't automatically mean a component needs *replacement*, but it does mean there's a problem that needs investigation by a mechanic.
* ABS Inoperative During Braking: This is a more serious issue. If you feel the brakes pulsate or grab harshly (the sensation of the ABS engaging and disengaging rapidly) *and* then feel the brakes are less effective than normal, it strongly suggests a problem with the ABS system.
* Brake Pedal Pulsation: While some pulsation can be normal (especially on older cars), *excessive* pulsation, especially when braking lightly, can indicate problems with the ABS system, particularly the wheel speed sensors.
* Spongy or Soft Brake Pedal: This is not solely an ABS problem; it could indicate many brake system issues. However, combined with other symptoms above, it could point to a larger problem that may include the ABS.
* Diagnostic Trouble Codes (DTCs): A mechanic can use an OBD-II scanner to read diagnostic trouble codes stored by the car's computer. These codes can pinpoint specific problems within the ABS system, such as a faulty sensor, pump, or control module.
What components might need replacing:
If diagnosis reveals a problem, the necessary repair might involve replacing one or more of the following:
* Wheel Speed Sensors: These sensors detect wheel rotation and are critical for the ABS to function. They're relatively inexpensive to replace.
* ABS Control Module (pump): This is the "brain" of the ABS system. It's a more expensive component to replace.
* ABS Hydraulic Control Unit: This unit contains the hydraulic components that modulate brake pressure. Repair or replacement is costly.
* Wiring or connectors: Damage to wiring or connectors can disrupt the ABS system's operation.
In short: Don't attempt to diagnose or repair the ABS system yourself unless you have extensive automotive electrical and hydraulic experience. If you notice any of the above symptoms, take your 1999 Mercury Sable to a qualified mechanic for diagnosis and repair. They will be able to determine the exact cause of the problem and recommend the necessary repairs. Ignoring ABS problems can lead to significantly reduced braking performance and increased risk of accidents.
