The ABS 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 an unexpected high drive voltage is detected when the valve relay is switched to OFF. (or unexpected low voltage is detected when the solenoid valve drive TR is switched to ON)
Item
Detecting Condition
DTC Strategy
? Internal monitoring
? Faulty HECU
Detect Mode
? Initial Check
? Outside the ABS control cycle
? Inside the ABS control cycle
? Diagnosis mode
? Failure mode
Enable Conditions
? If the valve relay is switched ON and corresponding solenoid driver OFF and the voltage of solenoid < 3.5±0.5V continuously for 56ms, the failure is detected.
? If the valve relay is switched ON and corresponding solenoid driver ON and the voltage of solenoid > 1.5±0.5V continuously for 56ms, the failure is detected.
Fail Safe
? System down. The ABS/EBD/TCS/ESP functions are inhibited.
- The valve relay and all solenoids are prevented from being switched on.
? The ABS/EBD/TCS/ESP warning lamps are activated.