CAN Communication Line Inspection

When measuring impedance, it is generally necessary to disconnect the circuit being tested from the power supply before hand. The vehicle's battery should therefore be disconnected and wait about four minutes to allow all capacitors in the system to discharge.

Inspection procedure for resistance test:

1. The CAN bus must be disconnected from the power supply.
2. The measurement is taken between the CAN High and CAN Low leads.
3. The measurement recorded may differ from the specified levels by a few ohms.

1. Ignition "OFF" and disconnect the battery and wait about four minutes.
2. Make sure all modules are properly connected.
3. Measure resistance between Pin No. 3 (C-CAN High) and Pin No. 11 (C-CAN Low) terminal of Data Link Connector (DLC).

   Specification:  Approx. 60Ω

4. Is measured value within specification?

   YES 

   • Check each module connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and then go to "VERIFICATION OF VEHICLE REPAIR " procedure.

   NO 

   • If the measured value is out of specification, go to "CAN resistor inspection" procedure.

     * If the measured value is approx. 0Ω, then check for short CAN communication line.

     * If the measured value is approx. 120Ω, then check for open CAN communication line of control module with resistor.

1. Ignition OFF.
2. Disconnect Battery (-) terminal.
3. Disconnect Instrument Cluster and Instrument BCM connectors.
4. Measure resistance between C-CAN Low and C-CAN High terminal of each BCM and Instrument Cluster.

   Specification:  About 120Ω

5. Is measured value within specification?

   YES 

   Go to "Short in CAN Communication Line Inspection" procedure.

   NO 

   • Carefully re-do this troubleshooting guide steps.
   • If problem still occurs, replace ECM or Instrument Cluster whichever has Defective resistor and then go to "VERIFICATION OF VEHICLE REPAIR " procedure.

1. Ignition "ON".
2. Measure voltage between Pin No. 3 (C-CAN High) terminal of Data Link Connector (DLC) and chassis ground.
3. Measure voltage between Pin No. 11 (C-CAN Low) terminal of Data Link Connector (DLC) and chassis ground.

   Specification:  CAN High Voltage - Approx. 2.6V/CAN Low Voltage - Approx. 2.4V

   Fig 1: C-CAN High And Low Signal Waveforms

   Courtesy of KIA MOTORS AMERICA, INC.
4. Is the measured value within specification?

   YES 

   • Fault might be intermittent and caused either by poor contact in connectors or wiring harness, or it has been repaired and control module memory is not cleared yet. Thoroughly check terminal of battery, all connectors (and connections) for looseness, bending, corrosion, contamination, deterioration, and/or damage.
   • Repair or replace as necessary and then go to "VERIFICATION OF VEHICLE REPAIR " procedure.

   NO 

   • Go to next procedure.
5. Ignition "OFF".
6. Disconnect Battery (-) terminal.
7. Refer to "appropriate service information" and disconnect BCM, ECM, TCM, HECU and other control unit connector that connected to C-CAN Communication circuit.
8. Measure resistance between Pin No. 3 (C-CAN High) terminal and Pin No. 11 (C-CAN Low) terminal of Data Link Connector (DLC).

   Specification:  Infinite (∞) Ω

9. Is measured value within specification?

   YES 

   • Go to "COMPONENT INSPECTION " procedure.

   NO 

   • Repair short in C-CAN Communication circuit or replace as necessary and then go to "VERIFICATION OF VEHICLE REPAIR " procedure.