This specification
applies to Hydraulic and Electronic Control Unit (HECU) of the Anti lock
Braking System(ABS).
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. | |
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. |
1. |
NORMAL BRAKING without ABS
Solenoid
valve
|
State
|
Valve
|
Passage
|
Pump
motor
|
Inlet
valve (NO)
|
OFF
|
OPEN
|
Master
cylinder ⇔ Wheel cylinder
|
OFF
|
Outlet
valve (NC)
|
OFF
|
CLOSE
|
Wheel
cylinder ⇔ Reservoir
|
When braking, the hydraulic pressure in the
TMC is increased. The pressure reaches the wheel brake via the
current less open inlet valve IV. The current less closed outlet
valve OV is closed. For the sake of simplicity the diagram is
limited to only the solenoid valve pair of one brake circuit. The
wheel speed is reduced as the brake pressure increases, in the
extreme case until the wheel locks.

|
2. |
With ABS
(1) |
DUMP MODE
Solenoid
|
State
|
Valve
|
Passage
|
Pump
motor
|
Inlet valve (NO)
|
ON
|
CLOSE
|
Master cylinder ⇔ Wheel
cylinder
|
ON
|
Outlet valve (NC)
|
ON
|
OPEN
|
Wheel cylinder ⇔
Reservoir
|
If the wheel speed decreases, there is
still a tendency to lock; the brake pressure on the
corresponding wheel must be reduced accordingly. For this, the
outlet valve OV is opened, the inlet valve IV remains
closed.
The brake pressure to the low-pressure
accumulator is reduced. The wheel in danger of locking gains
speed again.

|
(2) |
HOLD MODE
Solenoid
|
State
|
Valve
|
Passage
|
Pump
motor
|
Inlet valve (NO)
|
ON
|
CLOSE
|
Master cylinder ⇔ Wheel
cylinder
|
OFF
|
Outlet valve (NC)
|
OFF
|
CLOSE
|
Wheel cylinder ⇔
Reservoir
|
When a wheel (or several) tends to lock
the inlet valve IV is first closed to avoid a further increase
in brake pressure. The outlet valve OV remains closed: the
brake pressure is kept constant.

|
(3) |
INCREASE MODE
Solenoid
|
State
|
Valve
|
Passage
|
Pump
motor
|
Inlet valve (NO)
|
OFF
|
OPEN
|
Master cylinder ⇔ Wheel
cylinder
|
ON
|
Outlet valve (NC)
|
OFF
|
CLOSE
|
Wheel cylinder ⇔
Reservoir
|
For optimum brake from the certain wheel
acceleration a brake pressure increase is necessary. For this,
the inlet valve IV is opened and the outlet valve OV is
closed. The pump of the unit starts to run and aspirates the
necessary quantity of fluid from the Lowpressure accumulator,
in order to produce the necessary brake pressure for the
pressure increase phase in seconds.
With an increase in the brake pressure
the wheel speed is reduced. These control phases are repeated
until the ABS control unit no longer detects any tendency of
the wheels to lock.
During ABS control function, the
brake pedal only moves in accordance with the volume
requirement of the wheels. Becauseof a sudden change in
friction coefficient this pedal movement may increase
slightly. |

| |
3. |
Fail Safe Function
If there is a problem with the ABS system, the
Failsafe function operates, turning off the relay which supplies the
power to the solenoid valve, stoping the output of the control
signal, and turning on the ABS warning lamp in order to warn the
user of malfunction of the ABS system.
Conventional brake system operates under the
circumstance. |