Kia 2004.5 Spectra Service Technical Training page 187

2004.5 Spectra Technology
HYDRAULIC AND
ELECTRONIC CONTROL
UNIT (HECU)
COMPONENT OPERATION
ABS SELF-DIAGNOSIS
Brakes
The HECU is energized when the ignition key is turned
ON. After completing the initialization phase, the
HECU is ready for operation. In normal operating
condition, the HECU is ready (within specified limits,
i.e. voltage and temperature) to process the signals
sent by various sensors and switches.
The ABS system uses four passive wheel speed
sensors (WSS) to measure wheel speed. The wheel
signals are an analog signal that is converted to
square wave by the signal conditioning circuit within
the HECU. The signals from the wheels sensors are
compared to the remaining WSS to determine if there
is any slip, or traction loss. After processing inputs, the
HECU actuates the inlet and outlet solenoids according
to software control algorithms.
Self diagnosis can be classified into two categories:
• Initial diagnosis: performed right after the engine
starts.
• Regular diagnosis: performed continuously after the
initial diagnosis until the ignition switch is turned
OFF.
When a problem is detected by self-diagnosis, the
system turns:
• The solenoid valve OFF
• The pump motor OFF
• The ABS indicator light ON
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