Identifying a control module in the CAN network

Fig 1: Identifying Ignition ON

Courtesy of VOLVO CARS OF NORTH AMERICA.

Connect the battery.
Ignition on.
If the load on the CAN network is too high, this may be due to a control module transmitting faulty messages on the CAN network. This is called 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 fault may occur without any of the control modules storing a diagnostic trouble code (DTC). The voltage can be measured between the CAN cables in order to check the load on the CAN network.

The following applies for model year -2004:

Connect a voltmeter between the CAN cables. In the event of correct communication on the network, the average value of the voltage must be approximately 0.5 V (0.4 V to 0.6 V).

The following applies for model year 2004-:

Connect a voltmeter between the CAN cables. During correct CAN network communication, voltage should be about 0.6-1.4 V.

NOTE: For vehicles of later model years, the normal voltage value is slightly higher due to increased traffic between the control modules on the CAN network upon update of the electrical system.

In the event of a communication fault the voltage is significantly higher than the above specified values. In order to identify which control module has faulty communication, cut the power supply to one control module at a time. Check the voltage in the CAN cables again. The easiest way to cut the power supply is to remove the fuse(s) for the relevant control module. Repeat until the voltage between the CAN wiring drops to the normal level.

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: After a fault with "interfering" control modules, other control modules may remain in "Limp-Home mode" even when the ignition has been switched off and on several times. To remedy this, disconnect and reconnect the battery negative terminal to restore the control modules to normal function.

Other information
- See Battery, disconnecting

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