The ABS electronic control unit
M50
is supplied (at pin 2 and 6) directly by the battery via a line
protected by ABS maxifuse
B7
.
The ignition-operated supply (INT/A) reaches
pin 23 from the line protected by the fuse
B31
. The control
unit is earthed via pins 5 and 1 (
C12
).
The four sensors
K70, K71, K75, K76
send
the wheel speed sensors to pins 12-28, 15-16, 13-14 and 30-31 of
M50
respectively.
The brake pedal switch
I30
sends
an enablement signal to pin 32 of control unit
M50
. The
ABS is deactivated entirely unless the brake pedal is pressed.
Brake pedal signal
I30 is also used to
control the BRAKE lights (
See
E2021
BRAKE LIGHTS
)
and ENGINE CONTROL UNIT M10 (
See
E5030
PETROL ENGINE ELECTRONIC
MANAGEMENT
See
E5050
DIESEL ENGINES ELECTRONIC MANAGEMENT
).
A second contact on brake pedal
I30
(pins 3-4) sends a signal to control unit
M50
at pin 20.
the same signal is also sent to control unit M10, which manages
the CRUISE CONTROL system
See E5060 CRUISE CONTROL
.
Pin 37 of
M50 produces a speedometer
signal (average speed of all four wheels) which is directed to instrument
panel E50 - pin 2 of connector B (
See
E4010
INSTRUMENT PANEL
).
The ABS includes a self-diagnostic system:
when the control unit detects problems with the ABS, it sends a
signal from pin 20 of instrument
E50
- pin 18 of connector
C - which turns on the ABS fault warning light.
This warning light is of the type known
as 'smart' warning lights, because an inner control circuit causes
the warning light to light up even if the connection is broken or
if the circuit connecting warning light and control unit is short-circuited
to earth.
If the problems lie in the EBD function,
the control unti also sends a signal from pin 21 to instrument
E50
- pin 19 of connector C - to the low brake fluid and handbrake warning light.
Both signals sent to the instrument are
earth, and they turn on the warning lights since instrument
E50
is ignition-activated (INT/A) from a line protected by fuse
F1
of junction unit
B1
.
The self-test data can be read by connecting
to connector
R10
: it receives signals from pin 11 of the
control unit
M50
via the special diagnostic line.
Wiring diagram E7020 also shows the pins
of control unit
M50 that manages the VDC system (
See
E7022
VDC
) and the ASR/TCS
system (
See
E7021
ASR / TCS
).