Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Anti-Lock Brake System - 4-Wheel: Operation
When ignition is turned on, EHCU performs a self-check of the 4WAL electrical system. The Yellow ANTILOCK and Red BRAKE warning lights will come on for 2 seconds. ANTILOCK light should turn off if no electrical 4WAL faults are detected by EHCU. The Red BRAKE light may come on or stay on if parking brake is applied or a mechanical brake problem is detected.
Once vehicle speed has exceeded 8 MPH and driver has fully released the brake pedal, EHCU performs a self-check on electro-hydraulic portion of the system. This includes pump, control valves and reset switches. If EHCU detects a problem during this self-check or initial self-test, an indicator light will come on and 4WAL system will be disabled. A related trouble code will be stored.
When the brake pedal is depressed, voltage to the EHCU drops from 12 volts to one volt. At this point, EHCU monitors wheel speed through an AC signal generated by speed sensors located at each wheel. If the deceleration rate of wheel speed reaches a preprogrammed rate, EHCU will activate various control valves to prevent wheel lock-up by increasing or decreasing hydraulic pressure to each channel: left front, right front or rear wheels.
On 4WD models, a front-axle mounted switch is used to inform EHCU when vehicle is in 2WD or 4WD mode. Switch is open during 2WD operation, thus sending a one volt or less signal. During 4WD operation, switch closes, sending a 12-volt signal to EHCU. This signal causes EHCU to modify the anti-lock braking program for 4WD operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.