MULTIPLEX TROUBLESHOOTING GUIDE
Problem / Symptom Probable Causes Actions
Vehicle does not Start
from the dashboard
The Engine Stop pushbutton
located on the rear start
panel is depressed
Main electrical shut- off
switch is in the OFF position
1. Twist and pull the Engine Stop pushbutton to
place it in normal operating position, check
that the main electrical shut-off switch is in the
ON position and retry cranking from the
ignition switch
2. Start the vehicle from the engine
compartment using the rear start button
Vehicle does not Start
from the dashboard and
from the rear
DL0 (BBUS MUX) network
problem (Multiplex)
Module AE52 not powered
or is defective
Engine ECM does not
receive the ignition signal
Engine ECM is not powered
1. Verify that module AE52 is powered:
a. Check the DIAGNOSTICS menu of Driver
Information Display (DID). Select VIEW
ACTIVE FAULTS and ELECTRICAL. The
message “No Response ModA52, Active”,
indicates a power problem on the module or
a DL0 (BBUS MUX) network problem.
b. Check / reset circuit breaker CB5
c. Check / replace fuse F65
d. Probe gray connector on module to see if it is
powered.
2. Verify that the engine ECM is powered and
gets the ignition signal
a. Check / reset circuit breaker CB8 Check /
replace fuse F74
b. Check / reset circuit breaker CB2 Check /
replace fuse F78
PA-1652 Operator's Manual H3-45 Coach
B-2 Multiplex Troubleshooting
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