Hyundai Coupes/Sedans 1986-1993 Repair Guide

General Description


The 1992-93 Sonata uses a four channel ABS system which incorporates 6 solenoids (4 build decay & 2 isolation valves) and 4 speed sensors (1 for each wheel).

Anti-lock braking systems are designed to prevent locked-wheel skidding during hard braking or during braking on slippery surfaces. The front wheels of a vehicle cannot apply steering force if they are locked and sliding; the vehicle will continue in its previous direction of travel. The four wheel anti-lock brake system found on the Sonata holds each wheel just below the point of locking, thereby allowing some steering response and preventing the rear of the vehicle from sliding sideways.


The system monitors and compares wheel speed based on the inputs from the wheel speed sensors. The brake pressure is controlled according to the impending lock-up computations of the ABS control unit.

As a wheel approaches lock-up, the controller actuates the appropriate build/decay or isolation solenoid. Depending on the inputs from each respective wheel speed sensor, the ECM may cycle one of the 2 isolation valve; thus stopping the flow of fluid from the master cylinder to either the LF/RR or RF/LR brake circuit or the ECM may cycle any combination of the 4 build/decay solenoids; thus allowing the system to build brake pressure at the caliper or release (decay) pressure to the modulator sump. This reduces the tendency of the vehicle to skid sideways under braking.


See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: ABS system component locations-Sonata


See Figure 2

The modulator is located in the engine compartment, just forward of the left forward area of the engine compartment.

The hydraulic unit contains the 6 solenoid valves, 4 shuttles, 2 sumps, release check valves, proportioning valves, accumulator and the pump/motor assembly which provides pressurized fluid for the anti-lock system when necessary.

Hydraulic units are not interchangeable between vehicles. The units are not serviceable; if any fault occurs within the hydraulic unit, the entire unit must be replaced.

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Fig. Fig. 2: ABS modulator assembly-Sonata

Electronic Control Unit (ECU)

The ECU is located in the left forward engine compartment above the modulator assembly. The ECU receives inputs from the 4 speed sensors, brake light switch and the diagnostic connector. The ECU outputs signals to the 6 solenoid valves, ABS warning light relay and pump motor relay if detecting an impending wheel lock-up.

It is a micro-processor capable of dealing with many inputs simultaneously and controls the function of the solenoid valves within the hydraulic unit.

Wheel Speed Sensors and Toothed Rings

Each wheel is equipped with a magnetic sensor which produces a small AC voltage linear to wheel speed (11 Hz/mph). The sensor is mounted a fixed distance from a toothed ring which rotates with the wheel. The sensors are replaceable but not interchangeable; each must be fitted to its correct location. The toothed rings are replaceable although disassembly of the hub or axle shaft is required.

System Relays

See Figure 3

Three separate relays aid the operation of the ABS system. The ABS system and the pump/motor relays are located together on the left inner fender well under the hood, near the modulator and ECU.

The ABS warning lamp relay is located in the underhood relay box.

Each of the relays may be replaced in the usual fashion, although care must be taken to release wiring or connector clips before removing the relay.

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Fig. Fig. 3: Relay locations for the ABS system-Sonata

Warning Lamps

Both the amber ANTI-LOCK light and red BRAKE light are located on the instrument cluster. Each lamp warns the operator of a possible fault in the respective system. A fault in one system may cause the other lamp to illuminate depending on the nature and severity of the problem. The operation or behavior of the amber warning lamp is one of the prime diagnostic tools for the system.

At no time should the warning lamp be lit while the engine is running. Once the vehicle speed exceeds 3 mph, the system performs a self-check of the pump and solenoid function. Any failure in these circuits will cause the warning lamp to re-light, warning the operator of a problem.