Checking the resistance of the control area network (CAN) cables

Fig 1: Identifying Ignition In Off Position And Disconnecting Negative Cable From Battery

Courtesy of VOLVO CARS OF NORTH AMERICA.

• Disconnect the battery negative lead. The power to the network must be cut when taking resistance readings. The reading may otherwise be incorrect.
  NOTE:

  Also read: Battery, disconnecting

• Connect the adapter wiring to the central electronic module (CEM).

  HINT: Where a breakout box cannot be used, take readings from the rear of the affected connectors if possible. This prevents terminal pins and socket housings being damaged. 

  When taking readings on the low speed network 

  • When taking readings on the low speed network, the adapter wiring should be connected to the central electronic module (CEM) and the readings taken from there. The readings can also be taken in the connector for the power seat module (PSM). The advantage of using the adapter wiring connected to the central electronic module (CEM) is that all control modules can be connected to the network when taking readings and there is access to both the high speed and the low speed networks.

    This resistance reading only measures main arteries in the low speed network, not the junctions for the road traffic information module (RTI), accessory electronic module (AEM), power seat module (PSM), phone module (PHM), audio module (AUM), driver's door module (DDM) and passenger door module (PDM). See the Wiring diagram in the relevant Data communication service information.

  When taking readings on the high speed network 

  • When taking readings on the high speed network, the readings should be taken at the engine control module (ECM) using adapter wiring. The engine control module (ECM) must be connected. This resistance reading only takes readings from the main arteries in the high speed network. See the appropriate SYSTEM WIRING DIAGRAM article.

  Connect the ohmmeter to the terminals for CAN-L and CAN-H on the relevant network. Work the connectors and twist the cable harness. The resistance must be approximately 60 Ω. Permitted values are 55-65 Ω.

  Other information 

  • See Connecting the breakout box
  • See Checking wiring and terminals
  Fig 2: Identifying Ohmmeter

  Courtesy of VOLVO CARS OF NORTH AMERICA.
  Fig 3: Identifying Open-Circuit

  Courtesy of VOLVO CARS OF NORTH AMERICA.

Is the value OK? 

• YES 

  Refer to Checking a short-circuit in CAN cables 

• NO 

  Refer to Identifying fault causes in the CAN network