CAN Bus Communication Intermittent Test
CAN BUS COMMUNICATION INTERMITTENT TEST
1. RECORD AND ERASE ALL DTCS
With the scan tool, run a vehicle scan report (TSB 08-017-06) to record all DTCs from all modules. The vehicle scan report may be used later as an aid in diagnosing the intermittent condition.
Erase all DTCs from all modules.
Did any DTCs reappear and stay active?
Yes
- Go to and perform the appropriate diagnostic procedure.
No
- Go To 2
2. ATTEMPT TO REPRODUCE THE CONDITION
Monitor for and repair any active codes that appear as you work through the following steps.
- Check for any Technical Service Bulletins (TSB)s that may apply.
- Review the "When Monitored and "Set Conditions" for any DTCs that were stored and attempt to reproduce the conditions listed.
- Wiggle the wiring harness and connectors of the related circuit, sensor or component.
Was the source of the intermittent condition found?
Yes
- Repair as necessary.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
No
- Go To 3
3. ATTEMPT TO ISOLATE THE SYSTEM WITH THE INTERMITTENT CONDITION
In the event the intermittent condition cannot be duplicated, the following may aid in isolating the system involved.
The vehicle scan report can be a great diagnostic aid for tracking down the source of an intermittent condition when used in conjunction with the vehicle bus topology chart.
1. Obtain a copy of the vehicle scan report created previously.
2. Print the vehicle CAN Bus topology chart included with this test.
3. Using the ECU Info on the scan report, eliminate modules not equipped on this vehicle by crossing them off the topology chart.
4. On the topology chart, place a check mark next to or cross off any module that the scan report shows as reporting a DTC.
NOTE: Using the process of elimination, modules that are reporting codes are most likely operating properly. See if there is one module that is NOT reporting any codes. This is a likely area of interest to proceed with in the diagnosis of an intermittent condition.
Was any single module on any single bus not reporting any DTCs?
Yes
- Using the wiring diagram/schematic as a guide, inspect the wiring and connectors related to the component in question. Look for chafed, pierced, pinched, or partially broken wires and broken, bent, pushed out, spread, corroded, or contaminated terminals. Reconnect any disconnected components and harness connectors and make sure they are properly seated.
- If no problems are found, replace the module not reporting any DTCs.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
No
- Go To 4
4. ISOLATING THE REASON FOR TWO OR MORE MODULES NOT COMMUNICATING
NOTE: This procedure works well with intermittent module communication concerns. However with all the modules responding, the network topology will show all blue modules. Therefore, ignore the active or stored status for DTCs on the scan reports and look at the modules that had no response for a loss of power or ground. Use all module DTCs to determine which module was not responding intermittently.
Use the scan tool network topology to determine which module or modules are not communicating (modules will be highlighted in red).
The vehicle scan report can also be used to determine if two or more different modules, on the same bus or on different busses, are reporting stored codes for a common circuit.
If the modules that are not communicating are on different branches of a common bus or on different busses the most likely cause is a common power or ground that these modules share.
A loss of ground to the non-communicating module or modules can cause bus (+) or (-) circuit HIGH DTCs. Battery voltage supplied to most modules with no ground will pull bus voltage high.
A loss of power to the non-communicating module or modules can cause bus (+) or (-) circuit LOW DTCs.
Was the source of the intermittent condition located?
Yes
- Make the appropriate repairs.
- Perform the BODY VERIFICATION TEST. Body Verification Test.
No
- The problem cannot be found at this time. If repeated intermittent failures are encountered that cannot be reproduced and the condition has prompted multiple customer visits to the dealership, document any findings on the repair order.