The Electro-Hydraulic Control Unit (EHCU) is located in the left hand side of the engine compartment. The EHCU assembly includes the Electronic Brake Control module (EBCM) and the Brake Pressure Modulator Valve (BPMV). The EHCU regulates hydraulic pressure in the brake system during an antilock stop.
During model year 2000, the four-door utilities can be equipped with either a 325 ABS or 310 ABS. This is only due to production limitations of the new 325 ABS. While both ABSs are functionally the same, the 325 ABS differs from the 310 ABS in size and appearance. The main differences of the 325 ABSs are:
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The Electronic Brake Control Module (EBCM) is part of the EHCU. The EBCM is the electronic portion of the EHCU. The major function of the EBCM is to control the BPMV. Inputs to the EBCM include the following items:
Outputs of the EBCM include the following items:
A class 2 serial data line is also used for diagnostic service tools and assembly plant testing.
The EBCM monitors the speed of each wheel. If any wheel approaches lockup, the EBCM controls the solenoids (isolation solenoid and dump solenoid) in order to reduce brake pressure to the wheel approaching lockup. Once the wheel regains traction, brake pressure is increased until the wheel again approaches lockup. This cycle repeats until either the vehicle comes to a stop, the brake is released, or the wheel is no longer approaching lockup. The EBCM also runs self diagnostics in order to check for any system malfunctions. If the EBCM detects a malfunction with the system, the EBCM will illuminate the amber ABS indicator in order to alert the driver of the malfunction.
The Brake Pressure Modulator Valve (BPMV) is part of the EHCU. The BPMV is the hydraulic portion of the EHCU. The EBCM controls the BPMV. The BPMV is split into the following three hydraulic channels:
Each channel has an isolation valve and a dump valve. The front channels share a low pressure accumulator, attenuator, and a pump. The rear channel shares use of the pump, but uses it's own low pressure accumulator and attenuator.
The front Wheel Speed Sensors (WSS) are a magnetic coil/pickup type. Each WSS produces an AC voltage signal which is transmitted to the EBCM in order to indicate how fast the wheel is turning. The frequency and amplitude of the voltage signal is directly proportional to the speed of the wheel.
