* Low Brake Fluid: This is the first and most important thing to check. A significant leak in the brake system will rapidly deplete the fluid, leading to a spongy or nonexistent pedal. Inspect the brake lines, calipers, wheel cylinders, and master cylinder for leaks. Look for wet spots or dripping fluid. Top off the fluid ONLY if you find a leak – adding fluid without addressing the leak is dangerous.
* Master Cylinder Failure: The master cylinder is the pump that pressurizes the brake fluid. Internal failure (leaks, seals, etc.) can result in a loss of braking pressure. This is a critical component and requires immediate replacement.
* Brake Booster Failure: The brake booster assists your foot pressure, so a faulty booster will require significantly more force to brake, or result in a soft pedal. A vacuum leak in the booster's vacuum line can also cause this.
* Wheel Cylinder/Caliper Leak (Rear): Leaks in the wheel cylinders (rear brakes) or calipers (front and rear, depending on your model) allow brake fluid to escape, reducing braking pressure. This will often lead to a more gradual loss of braking power, though a sudden large leak can cause immediate failure.
* ABS System Malfunction: While the ABS light is often associated with sensor issues, a serious internal fault within the ABS module itself can interfere with normal braking pressure. This is less likely to cause a complete loss of braking, but can contribute to a spongy feeling and should be investigated.
* Brake Line Leak: A leak anywhere in the brake lines can cause a rapid or gradual loss of pressure. This is a serious safety hazard.
What to do:
1. Check the brake fluid level immediately. If it's low, *do not drive the truck*. Locate the leak before adding fluid.
2. Have the vehicle towed to a qualified mechanic. Do not attempt to diagnose or repair this yourself unless you have extensive experience working on brake systems. Brake failure is extremely dangerous.
3. Mention the ABS light to the mechanic. This provides additional information to aid in their diagnosis.
Ignoring this issue could lead to a dangerous accident. Safety should be your top priority.
