GM Full-Size Trucks 1988-1998 Repair Information

System Components


EHCU Valve

See Figure 1

The EHCU valve is mounted near or under the master cylinder and combination valve. The valve is not serviceable and must be replaced if malfunctioning.

Click image to see an enlarged view

Fig. Fig. 1: Exploded view of the Electro-Hydraulic Control Unit (EHCU)

Front Wheel Speed Sensors

With one exception, on both 2WD and 4WD vehicles, the front wheel speed sensors are permanently mounted to the brake rotor splash shield. With the exception of the 1992-98 Suburban, if the sensor fails the rotor and splash shield must be removed. On 4WD vehicles, the hub and bearing assembly must also be removed for access.

The front wheel speed sensors on 1992-98 4WD Suburban vehicles are removable without disassembly of the hub or brakes.

Rear Wheel Speed Sensors

Except for 1992-93 Suburban, the rear wheel speed sensors are held by 2 bolts at each rear wheel. The brake drum and primary brake shoe must be removed for access.

The 1992-93 Suburban receives the rear wheel speed signal from the Vehicle Speed Sensor (VSS) buffer. The VSS is located at the left rear of the transmission. The buffer, a unit for interpreting the electrical signal from the sensor, is located behind the instrument cluster. The buffer, formerly known as the digital ratio adapter controller (DRAC), is matched to the final drive and tire size of each vehicle. If the final drive or tire size is changed, the buffer unit must be replaced to maintain accurate speedometer/odometer readings and proper ABS function.