A0084313812 | Genuine Mercedes Benz® Anti Lock ABS Hydraulic Pump

1. Maintain Brake Fluid Pressure

• The hydraulic pump ensures that the brake system stays pressurized even when the ABS valves release pressure to prevent wheel lock.

• Without it, braking force would weaken during ABS operation.

2. Restore Pressure After Modulation

• When ABS reduces brake pressure to a wheel, some hydraulic fluid is diverted.

• The pump rebuilds and re-circulates that fluid back into the system, restoring full braking ability.

3. Ensure Continuous ABS Operation

• ABS can pulse up to 15 times per second during heavy braking.

• The pump provides the hydraulic flow and pressure needed for this rapid modulation — ensuring smooth, consistent braking cycles.

4. Prevent Brake Pedal Drop

• Without a functioning pump, the brake pedal might feel spongy, sink too low, or vibrate excessively during ABS use.

• The pump maintains firm pedal pressure for better driver control.

5. Improve Vehicle Stability

• By maintaining even hydraulic pressure across all wheels, the pump helps the ABS system prevent side skidding and loss of control on slippery or uneven surfaces.

6. Enable Steering During Emergency Braking

• When wheels lock up, you can’t steer.

• The hydraulic pump allows ABS to quickly modulate pressure, keeping the wheels rolling slightly so the driver can steer safely while braking hard.

7. Enhance Stopping Distance on Slippery Roads

• The pump helps ABS apply maximum safe pressure to each wheel without locking it up — shortening stopping distance on wet, icy, or gravel roads.

8. Support Other Vehicle Safety Systems

Modern cars use the ABS pump for more than just anti-lock braking:

• Traction Control System (TCS): Uses the pump to apply brakes to a spinning wheel and transfer power to wheels with grip.

• Electronic Stability Control (ESC): Uses the pump to individually brake wheels to correct oversteer or understeer.

• Hill-Start Assist & Automatic Braking Systems: Also depend on the pump for quick hydraulic pressure.

9. Maintain Equal Pressure Between Wheels

• The pump helps distribute pressure evenly to all wheels, especially when road conditions vary (like ice on one side, asphalt on the other).

10. Reduce Wear on Brake Components

• By preventing wheel lock and skidding, the pump reduces tire flat-spotting, brake pad glazing, and rotor stress — improving overall brake system longevity.

11. Provide Backup Pressure During Emergency Braking

• If the driver suddenly applies full brake force, the pump ensures the system can supply enough pressure instantly to all wheels without losing hydraulic balance.

1. ABS Warning Light On

• The ABS light illuminates on your dashboard.

• This is the most common and early sign.

• It means the ABS control module has detected a fault — often with the pump motor, pump relay, or internal pressure circuit.

• The vehicle may still brake normally, but ABS won’t engage in emergencies.

2. Wheels Lock Up During Hard Braking

• The ABS pump helps maintain brake pressure modulation.

• If it fails, the ABS can’t control pressure properly — causing wheels to lock when you brake hard.

• You’ll notice loss of steering control and possibly skidding, especially on wet or icy roads.

3. ABS Pump Running Constantly or Not at All

• Normally, the ABS pump activates only when ABS is needed (for example, during hard braking).

• A faulty relay, internal short, or stuck solenoid can cause the pump to:

  • Run continuously — even when not braking (you may hear a constant humming sound).

  • Or fail to run at all, meaning ABS won’t activate when needed.

4. Brake Pedal Feels Hard or Unresponsive

• If the pump fails to build or circulate pressure, the brake pedal can feel stiff or hard to press.

• This happens when the hydraulic pressure isn’t being properly boosted or balanced during braking.

5. Brake Pedal Feels Soft or Sinks to the Floor

• In some cases, the opposite happens — the pump can’t maintain pressure, causing a soft or spongy pedal feel.

• This may also indicate internal fluid leakage or air inside the ABS pump unit.

6. Unusual Noises from the Engine Bay

• You might hear buzzing, humming, or grinding noises when braking or shortly after turning on the ignition.

• A short “buzz” when you first start the car is normal (pump self-test).

• But continuous or harsh noises suggest the pump motor or internal valves are wearing out.

7. Brake Fluid Leaks Near ABS Unit

• The ABS pump is part of the hydraulic circuit — any cracks, worn seals, or internal corrosion can lead to fluid leaks around the ABS module.

• Low brake fluid levels can trigger the brake warning light and reduce braking performance.

8. Stored Diagnostic Trouble Codes (DTCs)

• When scanned with a diagnostic tool, codes related to the pump or motor may appear, such as:

  • C0110 – ABS Pump Motor Circuit Failure

  • C0265 – Pump Motor Relay Fault

  • C1214 – Hydraulic Pump Motor Circuit Malfunction

• These confirm electrical or mechanical failure inside the ABS pump assembly.

9. Reduced Stability or Traction Control Function

• Modern vehicles use the ABS pump for systems like ESC and TCS.

• If the pump fails, you may also see Traction Control (TCS) or Stability Control (ESC) lights on, and the car may lose those safety features.