* ABS Wheel Speed Sensor(s): These sensors are located near each wheel and measure the speed of rotation. A faulty sensor, a damaged wire to the sensor, or even just dirt or debris on the sensor can trigger the ABS light. This is the most common cause.
* ABS Control Module (Pump): This is the "brain" of the ABS system. A failing module is a serious problem and may require replacement. It's less common than a sensor issue but possible.
* Low Brake Fluid: Even though you've replaced rotors, low brake fluid can trigger both lights. Check your brake fluid reservoir to ensure it's at the correct level. If low, this points to a leak somewhere in the system.
* Wiring Issues: A short or break in the ABS wiring harness can cause problems. This can be difficult to diagnose.
* Brake Light Switch: While less likely given both lights are on, a faulty brake light switch *could* contribute to the problem, particularly if the brake light itself is acting erratically.
Troubleshooting Steps:
1. Check Brake Fluid: This is the easiest and quickest check. Top it off if low, but if it *remains* low after topping it off, you have a leak and need to find it ASAP.
2. Check the ABS Wheel Speed Sensors: Visually inspect the sensors for damage. Clean them carefully with a wire brush or compressed air. A scanner can read the sensor data to see if any are reporting erratic readings or no readings at all.
3. Have the System Scanned: Take your truck to an auto parts store (many offer free OBDII code scans) or a mechanic. A scan tool can read diagnostic trouble codes (DTCs) from the ABS module, which will pinpoint the likely problem.
4. Inspect Wiring: If a scan reveals no obvious sensor problems, carefully inspect the wiring harness for any damage, especially near the wheels and the ABS module.
Important Note: Driving with a malfunctioning ABS system is still possible, but ABS will be disabled. While you can still stop, the stopping distance will be longer and less controllable, especially on slick surfaces. Get this fixed as soon as possible.
