SERVICE MANUAL
  Applies to: Hyundai Coupe/Tiburon 1998-2000
GROUP
Steering System Electronic Power Steering System
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GENERAL 

The electronic power steering (EPS) system uses the same components as that of conventional power steering system. In addition, it has a angular velocity sensor located in steering column, a solenoid valve on power steering gear box, and a control unit inside the LH rear trunk.

To control the oil flow of steering gear box, a solenoid is provided and it functions by the current from control module which receives signal from VSS, TPS, and angular velocity sensor.

EPS performs the conventional power steering function in case a fail has occurred in the system.

EPS electronically controls the current to the solenoid of by-pass valve by input sensor's signal to control the hydraulic amount in cylinder chamber thereby varying the steering effort versus the hydraulic pressure according to vehicle speed.

ELECTRONIC POWER STEERING CONTROL MODULE

The EPSCM is installed in LH side trunk.

PIN LAYOUT
PIN NO.
DESCRIPTION
1
Solenoid current monitoring circuit
2
Data Link Connector
3
Angular velocity sensor
4
Steering wheel central position detection
5
Sensor signal from TPS
6
Solenoid valve operating circuit
7
Angular velocity sensor power input
8
Angular velocity sensor ground
9
Angular velocity sensor 2
10
Sensor signal from vehicle speed sensor
11
GROUND
12
Battery voltage
EPS CONTROL MODULE CIRCUIT
SOLENOID VALVE

A solenoid valve is provided in the gear box to control the flow of power steering oil. The solenoid valve is composed of a plunger, a releasing spring, a piston and a plunger.

The input current is varying from 0A to 1A according to the vehicle speed and steering wheel rotation speed and is controlled by EPS control module.

When the ignition switch is turned on, current is sent to the solenoid valve to push up the plunger and accordingly the piston contacting the plunger is pushed up while overcoming the spring force.

As the vehicle speed increasing the current flow to the solenoid decreased pulling down the piston bottom by the releasing spring force.

When the piston is pushed up, it closes the oil passing hole, therefore the power steering oil pressure is delivered into the cylinder without any interruption. But when the hole is opened as the piston is pulling down, some of the oil coming from the rotary valve is drained into reservoir via the hole inside the rotary valve.

NOTE
When it is necessary to remove the EPS gear box, be sure to disconnect the connector to avoid damage.
ANGULAR VELOCITY SENSOR

EPS equipped vehicle has a AVS in multifunction switch.

AVS is composed of a set of photo interrupters (light emitting diode, photo TR and slitted disc).

The slitted disc has 18 outer slits for detecting the steering wheel rotating direction and angular speed. And a inner slit is provided for checking whether the wheel position is within neutral or not.

2 sets of LED and photo TR check the rotation of steering wheel calculating the degrees per time through on, off photo TR, and a set of LED and photo TR is used to sense he wheel location.

With the signal from the sensors, the EPS control module miscellaneously decides the current flow to solenoid valve from 0A to 1A compensating steering wheel effort.

OPERATION
* LEFT TURN (COUNTERCLOCKWISE)

The power steering oil pump generates the oil pressure and the oil enters into the rotary valve. And the torsion bar is twisted by the force between the steering wheel rotation and the resistance of the tire to the ground.

At a high speed of vehicle, the oil passing the rotary valve comes into the solenoid valve through the lower hole and goes out through the upper hole flowing the connecting space of piston. At this time the piston is back away due to the spring force overcoming the solenoid plunger. The oil flows through the space between the piston and side wall.

And then the oil flows again into the rotary valve and finally drained to reservoir through the drain hole between the rotary valve and the torsion bar. Therefore the oil pump pressure does not affect to the steering effort.

"AT LOW SPEED"
"AT HIGH SPEED"

As the vehicle speed decreasing the hole of piston connecting the left chamber and right chamber is gradually closed as the oil pressure produced by oil pump is delivered to the left chamber. Therefore, the steering effort is reduced.

RIGHT TURN (CLOCKWISE)

The operation procedure of right turn is the reverse sequence of left turn.

"AT LOW SPEED"
"AT HIGH SPEED"
REMOVAL AND INSTALLATION

The removal and installation procedure is the same as that of conventional power steering system except the solenoid components and EPS control module.

The AVS is supplied as an multi-function switch assembly only.

NOTE
  1. The O-ring should not be re-used if removed.
  2. The spring seat is caulked not to be released. Do not attempt to remove the spring seat.
E.P.S. SOLENOID CHECK
SOLENOID CONTINUITY CHECK

Check for continuity, by using an ohmmeter, between the solenoid valve terminal and the disconnection of the solenoid valve connection.

FAIL SAFE FUNCTION

EPSCM performs the self-diagnosis within of the system to detect fault and sends fault code if found and it provides 4 fault codes. The flash code from EPSCM can be checked using test lamp or scan tool.

  1. Turn OFF the ignition switch and connect a pin of test lamp to the pin No. 13 of DLC and ground another pin. In case of using Scan tool, connect the DCL connector and cigar jack socket.

  1. Turn ON the ignition key and read the flash code of the test lamp or screen of Scan tool.

    If you check with Scan tool, be sure to press Enter key according to the specific vehicle configuration.

    THE CONTENTS OF FAIL SAFE CODE ARE AS FOLLOWING TABLE
    SCAN TOOL DISPLAY
    FLASH CODE
    ITEMS
    DESCRIPTION
    FAIL-SAFE
    11
    Battery voltage
    Flashes when the input battery voltage is less than 8V or more than 17V
    Solenoid current cut off
    12
    Vehicle speed sensor
    Flashes when the TPS voltage is 1.2V or more and receives no signal from VSS
    Off setting speed signal 80km/h
    13
    Monitoring current
    Flashes when the monitoring current is more than 1.28A for 1 sec.
    Solenoid current cut off



    Flashes when the solenoid wiring and circuit are open

    14
    Steering speed sensor
    Flashes when the angular velocity sensor wiring is open
    Controlled only by vehicle speed
    TOUBLESHOOTING
    Trouble symptom
    Trouble area
    Inspection item
    Steering wheel movement is heavy (When ignition key is turned to ON, no current flows through the solenoid)
    Steering gear and linkage
    Solenoid valve continuity


    By-pass valve

    Harness or fuse
    Blown fuse


    Remove the control unit connector and check the continuity in the solenoid harness (between terminals No.1 and No.6)

    Control module
    Turn the ignition key momentarily to ACC or LOCK and check if the fail-safe function is operating.


    Check for continuity in each harness and for abnormalities in the control module power circuit.
    While driving at medium or high speed, steering remains light
    Control module
    Use a tester to check the stationary steering effort.


    Check the solenoid current in relation to changes in vehicle speed.

    Steering gear and linkage
    Solenoid by-pass valve operation.
    NOTE
    For checking procedures for each problem, refer to the flow-chart type of troubleshooting guide on the following page.
    Trouble Symptom 1
    Trouble Symptom 2