Volvo C30 2007 Service And Repair Manual page 318

Connect OBDII-Box (951 3015) to the diagnostics socket.
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For general information about CAN-troubleshooting:
see GENERAL INFORMATION ABOUT FAULT-TRACING IN THE CAN NETWORK
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Checking for a short-circuit to ground
Measure resistance between the following connections on the OBDII-box/diagnostics socket.
#3 and #4 (ground). Measurement is shown in Fig. 11. The resistance should be above 1 kohms.
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#11 and #4 (ground). The resistance should be above 1 kohms.
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If resistance is below 1 kohms this indicates short-circuiting between the CAN-line and ground.
Checking for a short-circuit to voltage
Measure resistance between the following connections on the OBDII-box/diagnostics socket.
#3 and #16 (voltage). Measurement is shown in Fig. 11. The resistance should be above 1 kohms.
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#11 and #16 (voltage). The resistance should be above 1 kohms.
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If resistance is below 1 kohms this indicates short-circuiting between the CAN-line and voltage cable.
Twist the cable harness and wiggle connectors where they can be accessed along the cable harness during
every measurement, and note if the resistance changes to detect intermittent short-circuits or open circuit.
HINT: Part the CAN-net at suitable points to decide where a short-circuit may be found.
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.
Remedy wiring as necessary.
2012 Volvo C30 T-5
ELECTRICAL Body Electrical