In principle, the voltage measured in each cable in the CAN-net shall be the same at each control module
in the network. This means that the voltage-drop in the cable for CAN-H and CAN-L, respectively,
between the control modules should be very low. If there is a voltage-difference in the CAN-lines
between the diagnostics socket/Central electronic module (CEM) and a control module due to, e. g.,
contact resistance in a connector or branching, communication may be lost/interfered with. Check if there
is voltage-drop in the cable for CAN-H and CAN-L between the diagnostics socket/Central electronic
module (CEM) and the control module where there is problem with communication.
Carry out the following:
Measure voltage between the following connections on the OBDII-box/diagnostics socket.
#3 and corresponding connection on relevant control module for CAN-H. The voltage shall be
lower than 50 mV.
#11 and corresponding connection on relevant control module for CAN-L. The voltage shall be
lower than 50 mV.
If voltage is too high, this indicates too high contact resistance in cable, connector, or branching. Check
the circuit between the diagnostics socket and control module in question for contact resistance and
oxidation.
Remedy wiring as necessary.
Other information
see
CHECKING WIRING AND TERMINALS
NOTE:
After fault with control modules that interfere with communication, other
control modules may remain in Limp-Home (that is, they work with
reduced functionality) even when the ignition has been turned off and on a
few times. For certain faults in the CAN-net where control modules have
stopped communicating, it may help to disconnect/reconnect the battery
to "restart" the control module/CAN-net.
2012 Volvo C30 T-5
ELECTRICAL Body Electrical
