Identifying control module in CAN network

Fig 1: Identifying Ignition ON

Courtesy of VOLVO CARS OF NORTH AMERICA.

• Connect the battery

  Also read: Battery, disconnecting

• Ignition on

  If the load on the CAN network is too high, this may be due to a control module sending faulty messages on the CAN network (known as a disruptive control module). The fault may also be due to an intermittent short-circuit to supply voltage or ground in one of the CAN cables. This results in the control modules on the CAN network starting to send faulty messages. The faults can occur without a diagnostic trouble code (DTC) being stored by the control modules. The voltage can be measured between the CAN cables in order to check the load on the CAN network.

  Connect a voltmeter between the CAN cables. If the communication on the network is correct, the average voltage value should be approximately 0.5 V (0.4 V to 0.6 V). If there is a fault in the communication, the voltage reading will be approximately 0.7 V or higher.

  In order to identify from which control module the faulty communication is being transmitted, cut the supply voltage to one control module at a time and check the voltage in the CAN cables again. The easiest way to cut the supply voltage is to remove a fuse. Repeat until the voltage between the CAN cables drops to approximately 0.5 V.

  HINT: When the probable faulty control module has been identified, connect and disconnect the supply voltage to the control module a number of times to verify that the fault appears and disappears. 

  NOTE:

  Do not cut the power to the central electronic module (CEM) unless it is the last control module left to check.

  The control module that is communicating incorrectly must be replaced. Remedy as necessary.

  NOTE:

  Following a fault involving "disruptive" control modules, other modules may remain in "Limp-Home mode" even after switching the ignition off and on a number of times. To remedy this, disconnect and reconnect the battery negative terminal to restore the control modules to normal function.

Was a fault detected? 

• YES 

  Refer to Verification 

• NO 

  Refer to Downloading new software