Appendix I:
Fault Cases and Mistaken Repair Cases
HECU mistaken repair cases:
1. HECU replacement concerning ABS working sound
Case of HECU replacement for misjudging sounds of solenoid valve and motor as fault
when ABS is working
It is normal that there is noise during brake pressure decrease or increase when ABS is
working. The volume of noise varies according to different pressures to all wheels. It is
not a fault, which should be explained to clients.
When ECU diagnoses whether motor is working at the vehicle speed of 10 km/h for the
first time after start, a sensitive client may hear noise, which is also a normal ABS
working condition.
2. HECU replacement concerning EBD working sound
Case of HECU replacement for misjudging “click” sound from rear wheel as fault when
braking.
ABS can work as EBD. When rear wheel is blocked before front wheel, ABS will reduce
the brake pressure of rear wheel, which may cause noise. It is normal.
3. HECU replacement concerning braking deviation
Case of HECU replacement concerning the phenomenon that vehicle drifts to one side
when braking
ABS is an auxiliary brake equipment to calculate the speeds of all wheels by ECU and
maintain the best brake force and operation stability. When a fault occurs to HECU,
ECU will turn on the warning lamp after diagnosis. As a result, if braking deviation
occurs while ABS warning lamp is not turned on, other hydraulic brake equipments
should be checked.
Braking deviation may occur when ABS is working if brake hose is mistakenly
assembled.
4. Case of replacement concerning that ABS works during low speed (below 40 km/h)
brake
Case of HECU and sensor replacement concerning that ABS works during every low
speed brake
ABS may work during low speed braking according to road condition and brake
pressure. If ABS works every time, check whether the air gap of sensors of all wheels is
too large, whether the ring gear is disturbed and damaged.
Air gap adjustment method: After confirmation of part with abnormal air gap, replace or
burnish the mounting surface (contact area) of sensor and adjust to the specified air gap;
when disturbance occurs, a thin washer should be placed on the surface of sensor and
then adjust to specified air gap.
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