Question: I have a 2000 Chevy Silverado 1500 with the 5.3-liter engine, and the ABS and brake dash lights come on and stay on. But if I drive it for a while, turn the engine off, and then restart, they will turn off. It's not consistent. I'm thinking that the wheel sensors could be dirty.
Answer: There have been issues with dirty speed sensors causing unwanted or inadequate anti-lock brake application at low speeds. It's due to corrosion buildup at the wheel-speed-sensor mounting surface. This increases the air gap between the sensor tip and the rotating reluctor ring at the wheel hub, sending erroneous signals to the brake control module. But this problem does not typically set a diagnostic trouble code or turn on the ABS or Brake indicator lamps. Check the level of fluid in the brake master-cylinder reservoir. When fluid is low enough, the level sensor will turn on the brake warning light. But this signal is also seen by the brake control module, which may disable anti-lock brake operation and turn on the ABS indicator. This is often just a safety precaution to eliminate a potential safety hazard caused by ABS operation performed on a faulty brake system. If the brake fluid is low, inspect the entire system for leaks: master, hoses, lines, calipers, wheel cylinders, and connections. Often a low fluid level is normal, the result of brake lining wear causing caliper pistons to extend further out of the caliper bore to apply the brakes. You don't lose any fluid; it's just relocated from the master-cylinder reservoir to the calipers. If the fluid level is good, you have to scan the system, view the trouble codes, and diagnose from there.
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at firstname.lastname@example.org. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage -- visit Alex Steele at www.RealWorldAutomotive.com.