Subaru 602 - Open Circuit in Branch Bus

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June 2013
Electrical Systems Operation & Diagnosis Module (602)
Open Circuit in Branch Bus
When an open circuit occurs on the Branch Bus, communication with the control module connected
to that branch bus becomes disabled. In the example below, the BIU cannot communicate with
the TCM.
When an open circuit occurs in a branch bus, the resistance between HS-CAN High and HS-CAN
Low will be 60 Ohm, the same as under normal conditions.
Main bus
Branch bus
ELECTRIC
POWER
STEERING CM
COMBINATION
METER
BODY
INTEGRATED
UNIT
STEERING
ANGLE
SENSOR
VDC CM
120Ω120Ω
TCM
DATA LINK
CONNECTOR
A/C CM
ELECTRONIC
PARKING
BRAKE CM
ECM
Open Circuit Branch Bus
DLC TCM Connector
RT = ____________________ RT = ___________________
1 state 0 state 1 state 0 state
Voltage CAN High ________ _________ Voltage CAN High _______ ________
Voltage CAN Low ________ _________ Voltage CAN Low _______ ________
An open branch in the CAN results in the loss of communications with a control module. This
will result in the loss of all of the data that the control module supplied to the CAN as well
as the control that the control module provided to the vehicle. Diagnostics using resistance
or voltage will determine that the main CAN bus has no problems so you must check at the
affected control module.
Disconnect the affected control module. Failure to do so will result in the monitoring of signals or
voltage outputted from the control module that is not making contact with the CAN.
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