Dl0 (Bbus Mux) Connection On The Telltale Panel And The Hvac Control Unit; Spare Dl0 (Bbus Mux); Troubleshooting; Probing Voltage On The Multiplex Circuits - PREVOST H3-41 Maintenance Manual

SECTION 06: ELECTRICAL
isolated to help locate short-circuit on the DL0
(BBUS MUX).
In case of a short-circuit on the DL0 (BBUS
MUX) network, this affects all the modules and
they all act as "No response" in the error
messages of the
FAULTS/ELECTRICAL menu. To locate a short-
circuit, proceed by disconnecting one module
zone at a time while verifying if this makes
inactive the errors
connected. Connector C1 (front electrical &
service compartment)
modules at the rear of the vehicle from the
network. Connector C5 (front electrical & service
compartment) disconnects all the modules from
the entrance door & wiper control panel.
Connector C3 (rear electrical panel) disconnects
all the modules at the rear of the vehicle from
the network.
Example: Disconnect C5 and C1 and then verify the
status of the errors. If the front modules (A41 to A46)
now give inactive errors, which means short-circuit is
elsewhere than in the front electrical & service
compartment.
6.2 DL0 (BBUS MUX) CONNECTION ON
THE TELLTALE PANEL AND THE HVAC
CONTROL UNIT
The telltale panel module and HVAC module are
linked to the MCM by a DL0 (BBUS MUX)
connection. In case of a connection default, the
telltale panel LCD display shows "CAN", and on
the HVAC control unit, the temperature display
indicates "---". To confirm a connection default,
check that the fan speed on the driver's section
HVAC control unit cannot be adjusted.
Moreover, specific error messages from these 2
modules can be read in the ELECTRICAL menu.
NOTE
While downloading a new vehicle program in
the MCM from a computer, the DL0 (BBUS
MUX) network is temporarily interrupted and
therefore a DL0 (BBUS MUX) reference
appears in the telltale panel LCD display.
6.3

SPARE DL0 (BBUS MUX)

A spare DL0 (BBUS MUX) network is installed
between the front and the rear of the vehicle. It
has connectors installed at each end to facilitate
swapping from the regular DL0 (BBUS MUX)
34 PA1621 Maintenance Manual All Series | Revised Sept 2019
VIEW ACTIVE
in the modules still
disconnects all the
network to the spare DL0 (BBUS MUX) network.
Refer to the vehicle wiring diagram and section
4.6 for more information.
7.

TROUBLESHOOTING

7.1 PROBING VOLTAGE
MULTIPLEX CIRCUITS
Some Multiplex modules are supplied by 12
volts while others are supplied by 24 volts. The
12-volt or 24-volt information is found on the
modules symbol in the wiring diagram. Before
taking voltage readings to track the source of a
problem, first verify if the module is supplied by
12V or 24V, if not, residual voltage on the
module inputs/outputs can draw an erroneous
conclusion.
Inactive Multiplex output = Residual voltage of
18% to 33% of supply voltage.
Inactive Multiplex input = Residual voltage of
50% of supply voltage.
NOTE
o Verify on the wiring diagram whether the
voltage is 12V or 24V,
o For a 12V module: an active voltage would
be 12V or 0V but not in between. If you
measure the intermediate tensions (ex. 6V,
2V, or 4V) this must be interpreted as if the
input or the output is inactive.
For a 24V module: an active voltage would
o
be 24V or 0V but not in between. If you
measure the intermediate tensions (ex.
12V, 4V, or 8V) this must be interpreted as
if the input or the output is inactive.
ON THE