CAT 320D2 ECM seem not working

Cmark said: I don't quite understand what you mean. Are you testing both the Global CAN and Local CAN? Both wires of one twisted-pair are at 4.5v and both wires of the other twisted-pair are at 2.5v? Where are you taking the measurements? We are really only interested in the Global CAN measured at the ET connector. Can you show a screenshot of ET when it says it can't connect? Click to expand... Yes, I am testing both CAN lines. I am taking the measures at the ET connector. I will take a picture next time, but there is no connection. Nige said: Is the attached the procedure you are referring to.? I think the text in Step 3 on Page 5 may be relevant. Click to expand... Yes, that´s the procedure I was doing. Point 3 was the one I referred before. Edit: There is something "new". The voltage of one of the can line (sorry I don´t remember which one) is around 4.5v, but when I disconnect the switch panel it goes to 0v. But still with that disconnected the machine is not working

Another update: I tested the voltage of the CAN on another Cat 320 that I have (older), and the voltage is around 3.5v, as stated in step 3 of the procedure that Nige sent. I will now take all the cabin wiring apart, as it was repaired several times and I do not trust so much in that repairing.

borcom said: Yes, I am testing both CAN lines. I am taking the measures at the ET connector. Click to expand... At the ET connector there is only one CAN line: The Global CAN. The other twisted pair is CDL (Cat Data Link). CDL runs a different protocol to CAN and you will get different voltage readings. Did you unplug all the modules on the Global can as suggested earlier? If so then plug them back in one at a time and see what voltage you get at the ET connector and also if ET will connect.

These are an approximation of how CDL and CAN J1939 work. As you can see, you would expect to see different voltages on CAN high vs CAN low. On CDL you would expect to see roughly the same voltages.

I don’t believe you have proved an ECM failure. The fact that bypassing damaged cab connectors restored starting, combined with both ECMs disappearing from ET, points toward a common power/ground or Global CAN problem. OL from either CAN wire to ground with the batteries disconnected is correct. Concentrate only on pins F and G at the service connector—252 Green and 262 Yellow—not the CDL pair. Disconnect each Global CAN module individually and retry ET. Also load-test every ECM supply and ground because seeing 24 volts on a multimeter can be misleading through a high-resistance connection. Don’t replace or reflash an ECM until the network wiring and module isolation tests identify it. My leading suspect is still the previously repaired cab harness or one of its bulkhead connectors. The fact that manipulating those connectors changed the machine from no-crank to running is more persuasive than the ECM LED or the averaged CAN-voltage readings. But what do I know…

Cmark said: At the ET connector there is only one CAN line: The Global CAN. The other twisted pair is CDL (Cat Data Link). CDL runs a different protocol to CAN and you will get different voltage readings. Did you unplug all the modules on the Global can as suggested earlier? If so then plug them back in one at a time and see what voltage you get at the ET connector and also if ET will connect. Click to expand... Update: I unplug all the modules on the Global CAN and plug them one by one with ET connected. With Machine ECM only: error to connect ET. With Engine ECM only: error to connect ET. Both Machine ECM and Engine ECM: error to connect ET. Machine ECM and monitor: connect to ET, only monitor info. There is a connector from the ET to the wiring harness that goes outside the cabin to both ECM, y clean that one and still the same. ChrisMafera said: I don’t believe you have proved an ECM failure. The fact that bypassing damaged cab connectors restored starting, combined with both ECMs disappearing from ET, points toward a common power/ground or Global CAN problem. OL from either CAN wire to ground with the batteries disconnected is correct. Concentrate only on pins F and G at the service connector—252 Green and 262 Yellow—not the CDL pair. Disconnect each Global CAN module individually and retry ET. Also load-test every ECM supply and ground because seeing 24 volts on a multimeter can be misleading through a high-resistance connection. Don’t replace or reflash an ECM until the network wiring and module isolation tests identify it. My leading suspect is still the previously repaired cab harness or one of its bulkhead connectors. The fact that manipulating those connectors changed the machine from no-crank to running is more persuasive than the ECM LED or the averaged CAN-voltage readings. But what do I know… Click to expand... I review all the connections that were bypassed and seems ok, none of them are CAN lines, they are all fuse and relay outputs. I did a load-test on every connection and connector. Everything looks fine.

You have not mentioned the Product link. Have you unplugged it as well?

Cmark said: You have not mentioned the Product link. Have you unplugged it as well? Click to expand... Yes, that was unplugged also. I connected at the end but it was the same.

Something else that I didn´t mention yesterday, I also measure voltages of the Global CAN in the ET connector with everything disconnected and connecting one by one. The only one that gives voltage above 4.5 is connecting only Engine ECM, I have around 4.9v in the Global CAN. With Engine ECM and product link for example, I have around 2.5 on one cable and 1.7 in the other one. The same with everything else: Engine ECM, monitor, and dial.