Brake System > ESC(Electronic Stability Control) System

Component Location

General Description

The HECU consists of an ECU (Electronic Control Unit ) and a HCU( Hydraulic Control Unit).

The HCU portion of the assembly contains a pump motor, solenoid valves, and accumulator.

Increase and decrease of hydraulic pressure is opreated by electronic motor, according to a measured signal by wheel speed sensor.

The function of HCU is to increase, decrease or maintain the hydralic pressure supplied to a wheel cylinder by operating return pump according to HECU control signal while ABS control is active.

The ECU monitors various sensor and switch inputs.

These inputs are used to make decisions regarding HCU component operation.

DTC Description

The HECU monitors the operation of the IC components such as memory, register, A/D converter and so on.

The ECU sets this code when the EEPROM data read by the master processor is different than prior data written, or when the master/slave processor detects abnormal operation in RAM, Status Register, Interrupt, Timer, A/D converter or cycle time.

DTC Detecting Condition

Item

Detecting Condition

Possible cause

DTC
Strategy

•	Internal Monitoring

•	Faulty HECU

Enable
Conditions

•	When the MCU can't erase or write a data of the EEPROM.

•	When the master/slave processor detects abnormal operation in RAM, status register, interrupt, timer, A/D converter and cycle time.

Fail Safe

•	The ABS/EBD/ESC functions are inhibited.

•	The ABS/EBD/ESC warning lamps are activated.

Schematic Diagram

Terminal and Connector Inspection

1.	Many malfunctions in the electrical system are caused by poor harness(es) and terminal condition. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.

2.	Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.

Has a problem been found?

	▶ Repair as necessary and then go to "Verification Of Vehicle Repair" procedure.
	▶ Go to "Component Inspection" procedure.

Component Circuit Inspection

1.	Ignition "OFF" & Engine "OFF".

2.	Ignition "ON" & Engine "OFF".

3.	Connect scantool and select "Diagnostic Trouble Codes(DTCs)" mode.

4.	Using a scantool, Clear DTC.

5.	Select "Diagnostic Trouble Codes(DTCs)" mode again.

Are any DTCs present ?

	▶ Substitute with a known-good HECU and check for proper operation. If problem is corrected, replace HECU and then go to "Verification Of Vehicle Repair" procedure.
	▶ Fault is intermittent caused by faulty HECU or was repaired and HECU memory was not cleared. Go to "Verification Of Vehicle Repair" procedure.

Verification of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "Diagnostic Trouble Codes(DTCs)" mode.

2.	Using a scantool, Clear DTC.

3.	Operate the vehicle within DTC Detecting Condition in General Information.

4.	Using a scantool, Check DTC present.

Are any DTCs present ?

	▶ Go to the applicable troubleshooting procedure.
	▶ System performing to specification at this time.