Can Bus B

I have been having some issues with my batteries getting drawn down after sitting for just a week or two. Figured I had some type of parasitic draw. I had the son-in-law hook up the Auto Engenuity (AE) scanner and while there are no codes AE is indicating that the ECM is not communicating with the Can Bus B and the Can Bus B circuit is open. We pulled all the plugs and checked all the wiring and connections at both ends of the wiring harness and don't find any obvious issues. I searched the forum and did not find any discussions on this issue. Anyone have any ideas what is going on and the remedy?

 

I would first want to rule out the batteries as a potential source of the problem. I would disconnect the ground cable on each battery (after fully charging the batteries) and observe each battery state of charge after three days or so of no use. If they are fine, you know you have a problem elsewhere - if they have a low charge, then you know you have a battery problem and there is no need to look elsewhere.

Parasitic draws are normal for these trucks in order to keep computers in a standby condition - it's just how much draw is too much. I would expect normal draw to be around 30 - 50 milliamps, and that would be after the engine had been shut down for at least 30 minutes.

- John

 

Thanks John! The SIL said he charged the batteries and did a load test and everything checked out. Also, I replaced the batteries approximately 5000 miles ago at the time I rebuilt the motor. Odyssey batteries. Nevertheless, we decided to follow your suggestion and test the batteries and the following are the results:

Battery charged and hooked to the charger (just for information):
Passenger: 13.09 v
Driver: 13.07 v

All remaining tests are with the charger and negative cables removed.

Battery charged with negative cables removed immediately after removal of charger:
Passenger: 13.05-6 v
Driver: 13.01 v

Battery charged with negative cables removed plus 24 hours:
Passenger: 12.86 v
Driver: 12.79 v

Battery charged with negative cables removed plus 48 hours:
Passenger: 12.84 v
Driver: 12.76 v

Battery charged with negative cables removed plus 72 hours:
Passenger: 12.82 v
Driver: 12.75 v

All battery cables were replaced less than 100,000 miles ago so I believe that the batteries and cables are not the issue.

Below is a photo of my AutoEnginuity showing the current Diagnostic Trouble Codes. We think the codes showing under the TIPM may be related to my use of LED light bulbs. Note that many of the modules show "No response from module". I was not able to replicate the message that my SIL saw regarding no communication with the CAN BUS B. I note that otherwise the truck is running great.

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