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Anti-lock Brake SystemsAnti-lock Brake Systems

ABSABS

R. BortignonR. Bortignon

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ABSABS

• designed to control wheel lock-up to minimize stopping designed to control wheel lock-up to minimize stopping distance & help maintain steering controldistance & help maintain steering control

• is also used on vehicles with air brakesis also used on vehicles with air brakes

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ABS ComponentsABS Components

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How Many Channels?How Many Channels?

• a channel describes a brake hydraulic line that is capable a channel describes a brake hydraulic line that is capable of being controlled by the ABSof being controlled by the ABS

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Wheel Speed SensorWheel Speed Sensor• wheel speed sensor is a magnetic impulse sensorwheel speed sensor is a magnetic impulse sensor

works like a crankshaft position sensorworks like a crankshaft position sensor• creates an AC voltage signal as the tone ring rotates with creates an AC voltage signal as the tone ring rotates with

the wheelthe wheel• the AC voltage signal frequency changes as the wheel the AC voltage signal frequency changes as the wheel

speed changesspeed changes

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Modulating Brake Fluid PressureModulating Brake Fluid Pressure• EBCM activated solenoids modulate brake fluid pressureEBCM activated solenoids modulate brake fluid pressure• these solenoid valves can either…these solenoid valves can either…

hold (maintain) pressurehold (maintain) pressure dump (release) pressuredump (release) pressure increase pressureincrease pressure these solenoids can cycle the brakes 15 times/secondthese solenoids can cycle the brakes 15 times/second

Hold Pressure Dump Pressure Increase Pressure

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Electronic Brake Control Module (EBCM)Electronic Brake Control Module (EBCM)

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ABS “Electro-Hydraulic” ModulatorABS “Electro-Hydraulic” Modulator

• may be attached to the master cylindermay be attached to the master cylinder integral ABSintegral ABS

• may be mounted separate from the master cylindermay be mounted separate from the master cylinder non-integral ABSnon-integral ABS

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Servicing PrecautionsServicing Precautions• BleedingBleeding

may be done exactly the same as a non-ABS equipped vehiclemay be done exactly the same as a non-ABS equipped vehicle or may have specific bleeding proceduresor may have specific bleeding procedures

• when disconnecting brake lines, accumulator pressure may have when disconnecting brake lines, accumulator pressure may have to be relieved – can be up to 2800 PSI!to be relieved – can be up to 2800 PSI!

• read manufacturer's instructions carefully before beginning read manufacturer's instructions carefully before beginning repairs!repairs!

• ABS problem: always begin with a thorough inspection of the base ABS problem: always begin with a thorough inspection of the base brake system (non-ABS portion) firstbrake system (non-ABS portion) first

• brake warning light indicates a problem in the base braking brake warning light indicates a problem in the base braking system – not the ABSsystem – not the ABS

• ABS warning lamp indicates a problem within the ABSABS warning lamp indicates a problem within the ABS

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Warning LightsWarning Lights

• both brake warning lights should come on when the both brake warning lights should come on when the ignition is turned onignition is turned on this confirms that the warning circuit is operational this confirms that the warning circuit is operational

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Service TipsService Tips

• check wheel speed sensors for debris check wheel speed sensors for debris build-upbuild-up

• check tone rings for damage/debrischeck tone rings for damage/debris• check sensor wiring & connectorscheck sensor wiring & connectors• mismatched tire sizes confuses EBCMmismatched tire sizes confuses EBCM

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Service TipsService Tips

• do NOT push caliper pistons in without loosening bleeder do NOT push caliper pistons in without loosening bleeder screwscrew this prevents dirt from being pushed out of the caliper this prevents dirt from being pushed out of the caliper

& into the modulator & into the modulator • regular brake fluid flushes (every 2 years) minimize regular brake fluid flushes (every 2 years) minimize

modulator & solenoid problems & extends their life spanmodulator & solenoid problems & extends their life span