Hi all I am certainly not a CAN BUS expert but I have had some success diagnosing or repairing the network. I have written a list that has helped me, It's more of a reminder of what I have done previously - that has worked. Please feel free to add to it any tips or tricks you have picked up along the way. This list is not what you would normally find in the books or on the training courses.
1. Battery reset using test light wait 10 mins.
2. 60 ohms on network : Not all 16 pin DLC have the high speed CAN going straight on to pins 6 and 14. CAN gateways involved.
3. Check wiring diagram as some ECU'S CAN wiring runs THROUGH another ECU
4. If 120 ohms is found go to suspect ECU and do ohms measurement on that plug with it UNPLUGGED to prove that the 120 ohms is at the other end of the network and wiring is good.
5 if messages are present but corrupt suspect a failing ECU start by unplugging them one by one starting with the easiest first. ALWAYS check powers and grounds when you find suspect ECU.
6. Do a full scan of the car with a scan tool to see what is and isn't communicating to get a guide on where to look.
7. PERFORM WIGGLE TEST WHILST MONITORING SCOPE. (Wiring, connectors and ECU plugs)
8.Check the presence and voltage of the data whilst on road test as an intermittent short or open may be triggered by a bump in road, do not use a trigger as you may miss the event.
9. Try not to have scan tool connected when measuring CAN with scope as this could be corrupting data.
10. Weak battery, when cranking goes below 5 volts
Ask for and share advice on using the PicoScope kit to fix vehicles here.
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