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.
Hydraulic Control Unit (HCU)
The hydraulic control unit (HCU) consists of a valve body assembly, pump and a motor assembly. During normal braking, fluid from the brake master cylinder (2140) enters the HCU through two inlet ports located on the bottom of the HCU. The fluid then passes through four normally open isolation (ISO) valves, one to each of the four wheels. If the anti-lock brake control module (2B373) senses that a wheel is about to lock, the anti-lock brake control module pulses the appropriate isolation valve, which in turn closes that valve. This prevents any more fluid from entering the effected brake. The anti-lock brake control module then looks at that wheel again. If it is still decelerating, the anti-lock brake control module pulses the normally closed dump valve, which decreases the pressure trapped in the line.
Use the Manual With the Right Hardware
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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.
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