| TIBURON(GK) >2007 > G 2.7 DOHC > Brake System > ABS(Anti-Lock Brake System)>Description and Operation |

DESCRIPTION
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
- | Failsafe function
- | 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.
SCAN TOOL CHECK
1. | Turn the ignition switch OFF.
2. | Connect the scan tool 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 scan tool.
5. | After completion of the repair or correction of the problem, erase the stored fault codes using the clear key on the scan tool.
6. | Disconnect the scan tool from the 16P data link connector.
ABS CONTROL
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.