Antilock Brake Systems ABS R Bortignon 1 ABS

Anti-lock Brake Systems ABS R. Bortignon 1

ABS • designed to control wheel lock-up to minimize stopping distance & help maintain steering control • is also used on vehicles with air brakes 2

ABS Components 3

How Many Channels? • a channel describes a brake hydraulic line that is capable of being controlled by the ABS 4

Wheel Speed Sensor • wheel speed sensor is a magnetic impulse sensor Ø works like a crankshaft position sensor • creates an AC voltage signal as the tone ring rotates with the wheel • the AC voltage signal frequency changes as the wheel speed changes 5

Modulating Brake Fluid Pressure • EBCM activated solenoids modulate brake fluid pressure • these solenoid valves can either… Ø hold (maintain) pressure Ø dump (release) pressure Ø increase pressure Ø these solenoids can cycle the brakes 15 times/second Hold Pressure Dump Pressure Increase Pressure 6

Electronic Brake Control Module (EBCM) 7

ABS “Electro-Hydraulic” Modulator • may be attached to the master cylinder Ø integral ABS • may be mounted separate from the master cylinder Ø non-integral ABS 8

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Servicing Precautions • Bleeding Ø may be done exactly the same as a non-ABS equipped vehicle Ø or may have specific bleeding procedures • when disconnecting brake lines, accumulator pressure may have to be relieved – can be up to 2800 PSI! • read manufacturer's instructions carefully before beginning repairs! • ABS problem: always begin with a thorough inspection of the base brake system (non-ABS portion) first • brake warning light indicates a problem in the base braking system – not the ABS • ABS warning lamp indicates a problem within the ABS 10

Warning Lights • both brake warning lights should come on when the ignition is turned on Ø this confirms that the warning circuit is operational 11

Service Tips • check wheel speed sensors for debris build-up • check tone rings for damage/debris • check sensor wiring & connectors • mismatched tire sizes confuses EBCM 12

Service Tips • do NOT push caliper pistons in without loosening bleeder screw Ø this prevents dirt from being pushed out of the caliper & into the modulator • regular brake fluid flushes (every 2 years) minimize modulator & solenoid problems & extends their life span 13