* Faulty ABS Wheel Speed Sensor(s): These sensors monitor the speed of each wheel. If one or more sensors are malfunctioning (e.g., damaged wiring, dirty sensor, bad sensor itself), the ABS module interprets this as a wheel lock-up situation and activates the pump continuously to prevent it. This is the most frequent cause.
* Faulty ABS Module (Control Unit): The ABS module is the "brain" of the system. If it's malfunctioning, it can send incorrect signals, leading to the pump running constantly. This is a more expensive repair.
* Low Brake Fluid: While less likely to cause *continuous* running, critically low brake fluid can trigger the ABS pump as a safety mechanism. Check your brake fluid level.
* Wiring Issues: Damaged or corroded wiring within the ABS system can disrupt communication between the sensors, module, and pump, causing erratic behavior. Look for damaged, frayed, or corroded wires in the ABS wiring harness, particularly around the wheel speed sensors.
* ABS Pump Motor Failure (less common for continuous running): While a failing pump *can* cause it to run erratically or intermittently, a complete failure often results in the pump not running at all. A continuously running pump is more indicative of a signal problem from another part of the system telling it to run.
* Internal ABS Module Leakage: In some cases, internal leaks within the ABS module itself can cause it to malfunction.
Troubleshooting Steps:
1. Check Brake Fluid Level: This is the easiest and quickest check.
2. Check for ABS Warning Light: Is the ABS warning light illuminated on your dashboard? This is a strong indication of a problem within the ABS system.
3. Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner capable of reading ABS codes. This will give you a specific code indicating the likely source of the problem. Many auto parts stores offer free code reading.
4. Inspect Wheel Speed Sensors and Wiring: Visually inspect the sensors and their wiring harnesses for damage or corrosion. Clean the sensors if necessary.
Important Note: Continuously running the ABS pump can overheat and damage the pump itself. It's crucial to diagnose and repair the underlying problem as quickly as possible to prevent further damage. If you're not comfortable working on your vehicle's braking system, take it to a qualified mechanic. Improper repair can lead to dangerous braking problems.
