The HECU is composed of a ECU (Electronic Control Unit ) and an HCU( Hydraulic Control Unit), so the HECU hardware includes all solenoid valves inside the unit as well as the ECU.
Solenoid valves are switched to ON, OFF by HECU when the ABS is activated. Solenoid valves function is to increase, decrease or maintain the hydralic pressure supplied to a wheel cylinder.
The HECU monitors the operation of the valves by checking the drive circuit of the solenid valves, and then sets this code when the unexpcted drive voltage is detected.
For example, the HECU sets the DTC if the electrical feedback signal does not match the actuation signal for the corresponding valve.
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Voltege monitoring | ● Faulty HECU |
Case1 | Monitoring Period | ● Continuous |
Enable Conditions | ● The electrical feedback signal does not match the actuation signal for the corresponding valve for more than 30ms. - Current controlled valves and under voltage conditions :detection time is 80ms | |
Case2 | Monitoring Period | ● Immediately after power on ● every 20s - The Test is canceled if any control,valve actuation takes place or if the Vehicle is in motion and the BLS is on. |
Enable Conditions | ● A Fault is found if UVR is not within 0.1*battery voltage < valve relay voltage < 0.8*battery voltage. ● A Fault is found if valve relay voltage ≥ 0.2*battery voltage. - After that all valves are switched on sequential, valve relay voltage and valve feedback is measured. | |
Case3 | Monitoring Period | ● The Valve and Pump motor Test is performed once after ignition on if vehicle speed is >= 15 km/h. |
Enable Conditions | ● The valve and pump motor test detects electrical actuation malfunction of ABS valves. The test actuates all valves in series (to detect short cuts or shunts between the valve lines). Faults are detected if there is an error during the test. | |
Case4 | Monitoring Period | ● The drift test executes only once during an ignition Cycle. The test is triggered if the following conditions are fulfilled : 10min after power up or end of control 1. No BLS is applied 2. Brake pressure is < 10bar 3. Vehicle speed >15km/h 4. Vehicle acceleration > 0.5m/s2 5. Supply voltage > 11 volts. |
Enable Conditions | ● The drift test is executed only once during an ignition Cycle. If it detects partly shorted valve coils,almost defective coils or malfunction of the valve driver, a failure is reconized. | |
Fail Safe | ● Valve cannot be actuated or valve is incorrectly actuated. This may result in locked wheels or wheels without pressure. ● ABS/EBD/ESP function is prohibited. ● ABS/EBD/ESP warning lamp is turned ON. |
