Ford Mustang 1994-1998 Repair Guide

General Information


See Figures 1 and 2

Whenever service is performed on the Hydraulic Control Unit (HCU), a specific procedure must be performed to bleed the system to ensure that no air is trapped in the HCU. To perform this procedure, the New Generation Start (NGS) Tester, or an equivalent brake tool, is necessary.

The 1994-98 Mustang models were available with a Bosch 2U four-wheel Anti-lock Brake System (ABS) as an option. The ABS is designed to prevent wheel lock-up under heavy braking on almost any road surface by controlling the amount of brake system pressure applied to each wheel. By preventing the wheels from locking up, enhanced steering and braking integrity is maintained. During ABS operation, the driver of the vehicle will feel a pulsation in the brake pedal. Under normal conditions, the ABS allows the brake system to function in the same fashion as any conventional vacuum-boost brake system.

The Bosch 2U system is composed of the following components:

Hydraulic Control Unit (HCU)
ABS Control Module (ABS-CM)
Front and rear wheel ABS sensors

Click image to see an enlarged view

Fig. Fig. 1: The HCU and ABS-CM are combined into one assembly, which is mounted to the lower, right-hand radiator support in the engine compartment

The ABS works as follows:

ABS sensors mounted at each wheel on the vehicle electrically sense each tooth of the ABS sensor indicator ring as it passes through the ABS sensor's magnetic field. This data is sent to the ABS-CM, which translates the incoming signals, based upon their frequencies, into wheel speeds. Since the ABS-CM constantly monitors the rotational speeds of all four wheels, it can use this incoming data to activate the ABS only when an impending wheel lock-up is evident. In such an event, the ABS-CM decides which wheel(s) need(s) to be controlled, and sends the appropriate signal to the HCU. The HCU, in turn, manipulates (rapidly opens and closes) the appropriate internal solenoid valves to regulate brake pressure at the designated wheel(s). This manipulation of the internal solenoid valves is what results in the brake pedal pulsations felt by the vehicle operator.

Click image to see an enlarged view

Fig. Fig. 2: Anti-lock Brake System (ABS) electrical schematic

The HCU and ABS-CM are contained within one assembly. This assembly is located in the right-hand, lower front corner of the engine compartment, next to the bottom of the white radiator coolant reservoir.