Auto Service World
Feature   February 1, 2001   by Auto Service World


ABS and Traction Control equipped vehicles may have sophisticated braking and control systems, but the majority of brake problems on these vehicles still relate to the base braking system. It is useful for all involved in brake service to look for problems with this system first, before embarking on involved ABS/Traction Control diagnostics.

Here are some other tips:

Some ABS systems store brake fluid in an accumulator under high pressure. Failure to depressurize these types of anti-lock systems before servicing can cause physical injury. Technicians should follow service manual procedures.

Silicone-based brake fluids (DOT 5) are not recommended for ABS systems. Use the proper DOT 3 or DOT 4 brake fluid specified by the vehicle manufacturer. Note that DOT 5.1 fluid is a high temperature mineral-based fluid.

ABS and other on-board computers can be easily damaged by high electrical system voltage. Do not attempt to jump-start an ABS-equipped vehicle with a gasoline powered booster or 110-volt type battery charger on the fast charge/ boost setting.

All four tires must be of the same size and type. Failure to observe this rule can cause the ABS and/or Traction Control system to disengage and the warning light to come on.

Never unplug or reconnect any electrical ABS component with the ignition on. This can cause a current surge and damage one or more of the system components.

When installing any add-on electrical accessories (cell phones, audio systems, entertainment systems, alarms, etc.), it is important that any antennas or other wiring be located away from the ABS computer and sensor wiring. The magnetic field that is created produces electro-magnetic interference (EMI) that can affect the signals from the wheel speed sensor to the ABS computer.

When performing electrical welding on a vehicle, it is recommended that all of the computers be disconnected from the wiring harness to prevent possible damage. Care should be taken not to damage the connectors.

Whenever unitized wheel bearings, CV joints or half shafts, steering knuckles, or any other component that could affect the air gap between the wheel speed sensor and sensor ring has been replaced, the air gap must be checked.

When servicing disc brakes, open the bleeder screws and vent the brake fluid, if it is necessary to push the caliper pistons in. Sediment naturally collects in calipers over time. This sediment, if allowed to flow back into the master cylinder along with the brake fluid, can possibly damage the ABS hydraulic unit.

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