Anti-Lock Brake System: Operation: Self-Diagnosis

Self-diagnosis has 4 diagnostic modes. Initial diagnosis mode is performed just after engine starts until ABS indicator light goes off. Except ABS control mode is performed when ABS is not operating. During ABS control mode is performed when ABS is operating. During warning mode is performed when ABS indicator light is on.

When a problem is detected during self-diagnosis, ABS indicator light is turned on, a Diagnostic Trouble Code (DTC) is stored in memory and ABS system operation is changed to either system down mode or control inhibition mode.

During system down mode, pump motor relay is not operating, solenoid valve is in drive inhibition, CPU is operating (except during CPU failure) and restart condition occurs when ignition is cycled off, then on. During control inhibition mode, pump motor relay is not operating, solenoid valve is in drive inhibition, CPU is operating, and restart condition is automatic.

ABS control unit can store any number of DTCs. When the same DTC is detected more than once, the latest occurrence of the DTC overwrites the previous occurrence. DTCs are displayed in ascending order, not as they occur. Because DTCs are stored in EEPROM (nonvolatile) memory, they cannot be erased when battery is disconnected.