Most Likely Culprits (even if you think you've already checked them):
* ABS Wheel Speed Sensors: These are the most common cause of ABS problems. Even if you've *replaced* them, consider these points:
* Incorrect Installation: A slightly misaligned or improperly seated sensor can cause intermittent issues. Double-check their alignment and ensure a clean, secure connection.
* Damaged Wiring: The wiring harness to the sensors can be damaged (chafing, rodent damage, etc.), even if the sensors themselves are new. Inspect the wiring carefully from the sensor all the way back to the ABS module.
* Faulty Sensor (again): A new sensor could be defective right out of the box (though less likely).
* ABS Module (Hydraulic Control Unit): This is the "brain" of the ABS system. Internal failures within the module can cause erratic behavior, including pulsating pedals and intermittent ABS function. This is a costly part to replace, but often the root cause after other components have been eliminated. A professional scan tool might reveal fault codes pointing directly to the module.
* ABS Pump Motor: While less common, a failing pump motor can cause pulsations in the brake pedal. This is often accompanied by unusual noises from the ABS module area.
* Brake Lines/Components: Though less likely if removing the ABS fuse makes it work normally, carefully inspect brake lines for leaks, blockages, or corrosion which could impact pressure modulation, even indirectly affecting the ABS system's readings and causing the pulsation.
Troubleshooting Steps:
1. Professional Scan: Take your truck to a reputable mechanic or dealership and have them perform a thorough diagnostic scan using a scan tool capable of reading ABS codes. This is crucial. Generic OBDII scanners often don't read ABS codes fully.
2. Careful Visual Inspection: Inspect *all* wiring related to the ABS system, paying close attention to areas prone to wear and tear.
3. Verify Sensor Readings: If you have access to a professional scan tool, check the live data for the wheel speed sensors. Erratic or inconsistent readings pinpoint a faulty sensor or wiring.
4. Actuation Test (Professional): A mechanic can perform an actuation test on the ABS components to check for proper functionality of the pump motor and valves within the ABS module.
Important Note: Driving with a faulty ABS system is not ideal. While removing the fuse makes the brakes functional, you lose the crucial anti-lock function, which can significantly increase stopping distances in emergency situations. Get this fixed professionally as soon as possible.
