Identifying A Control Module In the CAN Network

Identifying A Control Module In The CAN Network
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.

NOTE: It is not necessarily the control module(s) that stored the diagnostic trouble code (DTC) that is communicating faultily. Faulty messages can come from any control module in the same section of the CAN network. However, faulty communication in one network cannot affect the communication on the other network. In other words, faulty communication on the LS-CAN cannot disrupt communication on the HS-CAN and vice versa.

Check communication/load on CAN-net by measuring voltage between #B1 (#1) and # B13 (#13). The average value of the voltage must be approximately 0.6-1.4 V. 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.

NOTE: When connecting and disconnecting individual control modules, other diagnostic trouble codes (DTCs) may be stored in certain control modules.

HINT: When the suspected 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. Switch off the ignition between each check.

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

A control module that is communicating incorrectly must be replaced. See Repairing and installing/Removing, replacing and installing.

NOTE: Following a fault involving control modules that disrupt communication, other control modules may remain in Limp-Home mode (i.e. they work but with limited functionality) 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.

Continue: Refer to Reading Off DTCs From All Systems Before Erasing. Reading Off DTCs From All Systems Before Erasing