This specification
applies to Hydraulic and Electronic Control Unit (HECU) of the Anti lock
Braking System(ABS) and Traction Control System(TCS).
This HECU has the
functions as follows:
- |
Input of signal from the wheel speed sensors
attached to each wheel. |
- |
Control of braking force and traction
force |
- |
Self diagnosis
function |
- |
Interface with the external diagnosis
tester |
Operation
The HECU shall be put
into operation by switching on the operating voltage (IGN).
On completion of the
initialization phase, the HECU shall be ready for operation.
In the operating
condition, the HECU shall be ready, within the specified limits (voltage
and temperature), to process the signals offered by the various sensors
and switches in accordance with the control algorithm defined by the
software and to control the hydraulic and electrical
actuators.
The HECU shall receive
wheel speed signal from the four inductive wheel sensors.
The wheel signals are
converted to square wave by the signal conditioning circuit and given as
input to the μ- processor.
The sensor connections
shall be monitored for short-circuit and inter-ruption and then in the
event of 2 sensor failures, the HECU shall shut down the
system.
When one side of the
valve coil is connected to the positive voltage that is provided through
the valve relay and the other side is connected to the ground by the
MOSFET, the solenoid valve goes into operation.
The electrical function
of the valves are always monitored by the valve test pulse under normal
operation conditions.
When overvoltage is
detected(above 16V), the HECU switches off the valve relay and shuts down
the system. When voltage is returned to operating range, the system goes
back to the normal condition after the initialization phase.
In the event of
undervoltage(below 10V), ABS control shall be inhibited and the warning
lamp shall be turned on.
When voltage is returned
to operating range, the warning lamp is switched off and the HECU returns
to normal operating mode.
The pump motor operates
when the ABS is functioning.
The HECU performs a pump
motor test at a speed of 20km/h once after turned the Ignition switch on.
You may hear the motor operate at this time, but it is
normal.
Malfunctions or failures
detected by the HECU are encoded on the HECU, stored in a EEPROM and read
out by diagnostic equipment (hi-scan pro) when the ignition switch is
turned on.
Warning lamp control

1. |
ABS warning lamp module
The ABS warning lamp module indicates the
operating condition of the ABS.
The ABS warning lamp is turned on under the
following conditions.
A. |
During the initialization phase after
ignition switch ON (3
seconds). |
B. |
In the event of inhibition of ABS
functions by failure. |
C. |
When the system ECU is shut down even
though ignition power is
applied. |
D. |
During diagnostic
mode. |
E. |
When the HECU connector is
disconnected. | |
2. |
EBD warning lamp module
The EBD warning lamp module indicates the
operating condition of the EBD. However, in case the parking brake
switch is turned on, the EBD warning lamp is always turned on
regardless of EBD functions.
The EBD warning lamp is turned on under the
following conditions.
A. |
During the initialization phase after
ignition switch ON. (3
seconds). |
B. |
When the system ECU is shut down even
though ignition power is
applied. |
C. |
When the parking brake switch is ON or
brake fluid is low level. |
D. |
In the event of inhibition of EBD
functions by
failure. | |
3. |
TCS lamp module
The TCS warning lamp module indicates the
operating condition of the TCS.
The TCS warning lamp is turned on under the
following conditions:
A. |
During the initialization phase after
ignition switch ON (3
seconds). |
B. |
In the event of inhibition of TCS
functions by failure. |
C. |
When the TCS OFF switch is turned
on. |
TCS function lamp is turned on when the TCS
functions are operating
(Blinking-2Hz). |
Diagnostic trouble code (DTC)
1. |
If the CPU cannot be activated or the CPU
fails, the ABS indicator comes on, but the DTC is not
memorized. |
2. |
The memory can hold any number of DTCs.
However, when the same DTC is detected more than once, the later one
is written over the old one.
Therefore, when the same problem is detected
repeatedly, it is memorized as one
DTC. |
3. |
The DTCs are indicated in the order they
occur. |
4. |
The DTCs are memorized in the EEPROM (non -
volatile memory). Therefore, the memorized DTCs cannot be canceled
by disconnecting the battery. Perform the specified procedures to
erase the DTCs. |
Self-diagnosis
1. |
Self diagnosis can be classified into two
categories:
A. |
Initial diagnosis:
Performed right after the engine starts
and until the ABS indicator goes
off. |
B. |
Regular diagnosis:
Performed right after the initial
diagnosis until the ignition switch is turned
OFF. | |
2. |
When a problem is detected by self-diagnosis,
the system:
A. |
Turns the solenoid valve
OFF |
B. |
Turns the pump motor
OFF |
C. |
Turns the ABS indicator
ON | |
How to troubleshoot ABS DTC
1. |
Question the customer about the conditions
when the problem occured, and try to reproduce the same conditions
for troubleshooting. Find out when the ABS indicator came on, such
as during initial diagnosis, during ABS control, after ABS control,
when vehicle speed was at a certain speed,
etc. |
2. |
When the ABS indicator does not come on during
the test-drive, but troubleshooting is performed based on the DTC.
check for loose connectors, poor contact of the terminals, etc.
before you start troubleshooting. |
3. |
After troubleshooting, erase the DTC and
test-drive the vehicle. Be sure the ABS indicator does not come
on. |
HI-SCAN (PRO) CHECK
1. |
Turn the ignition switch
OFF. |
2. |
Connect the Hi-scan (pro) to the 16P data link
connector located underneath the lower crash pad panel.


|
3. |
Turn the ignition switch
ON. |
4. |
Check for diagnostic trouble codes using the
Hi-scan (pro). |
5. |
After completion of the repair or correction
of the problem, erase the stored fault codes using the clear key on
the Hi-scan (pro). |
6. |
Disconnect the Hi-scan (pro) from the 16P data
link connector. |
ABS OPERATION
1. |
NORMAL BRAKING
Solenoid
valve
|
State
|
Valve
|
Passage
|
Pump
motor
|
IN
(NO)
|
OFF
|
OPEN
|
Master
cylinder ⇔ Wheel cylinder
|
OFF
|
OUT
(NC)
|
OFF
|
CLOSE
|
Wheel
cylinder ⇔ Reservoir
|
Under
the normal braking, voltage is not supplied to solenoid valve,
inlet valve is opened and outlet valve is
closed. When the brake is
depressed, brake fluid is supplied to the wheel cylindervia
solenoid valve to activate the brake. When the brake is released, brake fluid is back to
the master cylinder via inlet valve and check
valve.
|
|
2. |
DUMP MODE
Solenoid
valve
|
State
|
Valve
|
Passage
|
Pump
motor
|
IN
(NO)
|
ON
|
CLOSE
|
Master
cylinder ⇔ Wheel cylinder
|
ON
|
OUT
(NC)
|
ON
|
OPEN
|
Wheel
cylinder ⇔ Reservoir
|
Under
the emergency braking, if the wheels start to lock up, HECU
sends a signal to the solenoid valve to decrease the
brakefluid, then voltage is supplied to each solenoid. At this
time inlet valve is closed and brake fluid is blocked from the
mastercylinder. Conversely outlet valve is opened and brake
fluid passes through wheel cylinder to reservoir, resulting in
pressure
decrease.
|
|
3. |
HOLD MODE
Solenoid
valve
|
State
|
Valve
|
Passage
|
Pump
motor
|
IN
(NO)
|
ON
|
CLOSE
|
Master
cylinder ⇔ Wheel cylinder
|
ON
|
OUT
(NC)
|
OFF
|
CLOSE
|
Wheel
cylinder ⇔ Reservoir
|
When
the brake fluid pressure is maximally decreased in wheel
cylinder, HECU sends a signal to solenoid valve to keep the
fluidpressure, voltage is supplied to inlet valve but it is
not supplied to outlet valve. At this time inlet and outlet
valves are closed and brake fluid is kept in wheel
cylinder.
|
|
4. |
INCREASE MODE
Solenoid
valve
|
State
|
Valve
|
Passage
|
Pump
motor
|
IN
(NO)
|
OFF
|
OPEN
|
Master
cylinder ⇔ Wheel cylinder
|
ON
|
OUT
(NC)
|
OFF
|
CLOSE
|
Wheel
cylinder ⇔ Reservoir
|
If HECU
determines there's no lock-up in the wheel, HECU cuts voltage
to solenoid valve. So voltage is not supplied to each solenoid
valve, brake fluid passes through the inlet valve to wheel
cylinder, resulting in pressure
increase.
|
|
TRACTION CONTROL SYSTEM (TCS) OPERATION
1. |
NORMAL MODE
Solenoid
valve
|
State
|
Valve
|
Motor pump
|
TC valve
|
IN
(NO)
|
OFF
|
OPEN
|
OFF
|
OFF
|
OUT
(NC)
|
OFF
|
CLOSE
|
•
|
In the normal driving condition,
TC valve (normally open) is the passage between the
master cylinder and the each wheel
cylinder. |
•
|
When brake pedal is applied, brake
pressure is delivered to the wheel cylinders via NO-TC
valve and all solenoid valves inside the hydraulic unit
are deactivated. |
•
|
In case of TCS malfunction it does
not affect brake
operation. | |
|
2. |
PRESSURE INCREASE MODE
Solenoid
valve
|
State
|
Valve
|
Motor pump
|
TC valve
|
IN
(NO)
|
FRONT:
OFF REAR: ON
|
FRONT:
OPEN REAR: CLOSE
|
ON
|
ON
|
OUT
(NC)
|
OFF
|
CLOSE
|
•
|
If a front wheel spin is detected,
TCS begins a brake control to decrease a wheel
spin. |
•
|
Hydraulic shuttle valve (HSV) is
opened.
Brake fluid is supplied from the
master cylinder by motor operation to the spin wheel via
HSV. |
•
|
TC valve is closed
(ON).
Brake pressure generated from
motor pump is delivered only to the front
wheel. |
•
|
Inlet valve remains open to
deliver the brake pressure generated from motor pump to
the spinning
wheels. | |
|
3. |
PRESSURE DUMP MODE
Solenoid
valve
|
State
|
Valve
|
Motor pump
|
TC valve
|
IN
(NO)
|
ON
|
CLOSE
|
ON
|
ON
|
OUT
(NC)
|
FRONT:
ON REAR: OFF
|
FRONT:
OPEN REAR:
CLOSE
|
•
|
When the wheel deceleration is
under the threshold and the wheel spin is reduced under
a slip threshold, applied brake pressure is reduced to
get a optimum traction
force. |
•
|
Outlet valve is open to release
the brake pressure and inlet valve is closed to block
the pressure increase from the motor
pump. |
•
|
Hydraulic shuttle valve (HSV)
remains opened, TC valve is
ON. |
•
|
Motor is ON, to dump the brake
fluid being released from the lock-up
wheel. | |
|
4. |
PRESSURE HOLD MODE
Solenoid
valve
|
State
|
Valve
|
Motor pump
|
TC valve
|
IN
(NO)
|
ON
|
CLOSE
|
ON
|
ON
|
OUT
(NC)
|
OFF
|
CLOSE
|
|
TRACTION CONTROL SYSTEM (TCS) FUNCTION
1. |
Main performance
A. |
Traction: Lower vibration and higher
launchability, accelerationand climbability by slip
control. |
B. |
Cornering and passing: Stable cornering
and passing. |
C. |
Steering stability: Control traction
force traverse vector prior to provide easy turning when
turning the steering
wheel. | |
2. |
General TCS features
A. |
Improved drivability. Minor operation of
acceleration is not necessary in launching and acceleration on
slippery road. |
B. |
More stable cornering by stable
acceleration on normal road
condition. |
C. |
TCS system will compare vehicle speed
received from rear wheel speed sensor and driving wheel speed
from front wheel speed sensor on slippery road condition, and
provide optimum slipping rate of driving
wheels. | |
FULL TRACTION CONTROL SYSTEM (FTCS)
1. |
The ABS control module (HECU) controls TCS
control too. |
2. |
HECU will compare signals from front (driving)
and rear wheel speed sensors to detect driving wheels
slip. |
3. |
Upon detecting driving wheels slip, HECU will
perform TCS control. The TCS control will include brake TCS (BTCS)
control. |
4. |
HECU will transmit engine torque reduction
request, fuel cut cylinder number, and TCS control request signals
in accordance with slip level to engine ECM and TCM through BUS line
which will provide CAN communication for TCS
control. |
5. |
Engine ECM will perform fuel cut as requested
by HECU and retard ignition timing as per engine torque reduction
request signal. |
6. |
TCM will hold shift position by TCS control
time according to TCS operation signal. Then enhanced acceleration
by kick-down will not occur. |

BRAKE TRACTION CONTROL SYSTEM (BTCS)
1. |
On TCS control, only brake control will be
performed. (engine and TCM control will not
happen) |
2. |
Controlled by motor pump output
pressure. |
EBD (ELECTRONIC BRAKE-FORCE DISTRIBUTION)
OPERATION
ADVANTAGES
- |
Function improvement of the base-brake
system. |
- |
Compensation for the different friction
coefficients. |
- |
Elimination of the proportioning
valve. |
- |
Failure recognition by the warning
lamp. |
Comparison between Proportioning valve and
EBD

FAIL SAFE
FAIL CAUSE
|
SYSTEM
|
WARNING LAMP
|
ABS
|
EBD
|
ABS
|
EBD
|
None
|
ON
|
ON
|
OFF
|
OFF
|
1-Wheel
speed sensor failure
|
OFF
|
ON
|
ON
|
OFF
|
Pump
malfunction
|
OFF
|
ON
|
ON
|
OFF
|
Low
voltage
|
OFF
|
ON
|
ON
|
OFF
|
2 or more
wheel speed sensor failure Solenoid valve
failure HECU malfunction Valve relay failure Over
voltage Other failure
|
OFF
|
OFF
|
ON
|
ON
|