ProMaster City CAN-B Question

Mike Technician Atlanta, Georgia Posted   Latest  
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Electrical
Network Communications
2017 Ram ProMaster City Tradesman 2.4L (B ED6) 9-spd (948TE)

I was working on this one today and took waveforms of CAN B and CAN C. CAN C behaved like I expected. When communication ceased high and low went to 2.5v and when everything shut down, both dropped to zero. CAN B's waveform itself seemed ok. High went from 5v to 10v and low went from 5v to 0. I'm assuming that's normal range for B. What was weird is when everything shut down, CAN B high (DLC pin 1) went to 0v and CAN B low (pin 9) went to 11v and stayed there. Draw was 49ma so I don't think this is a case of something staying on, although I could be wrong. And there were no U codes to indicate a problem.

Should CAN B do that or do I have a problem there that needs further investigation?

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
   

This is how fault-tolerant 83.3kbps CAN-B bus sleeps on Chrysler products. diag​.​net/file/f3zmm9cog… ​ Your description of active CAN high from 5v to 10v is puzzling to me. Could you double-check?

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Mike Technician
Atlanta, Georgia
Mike Default
 

I have another one in today for some AC work. I will get a waveform. Thanks for the info. I looked in AllDAta and could not find that.

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Richard Instructor
Palmetto, Florida
Richard Default
 

Can B is more than likely “sleeping with one eye open“ because something needs to stay awake watching for keyfob/remote/door jamb switch.

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Mike Technician
Atlanta, Georgia
Mike Default
 

That's kind of what I was wondering. Thanks.

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Ray Diagnostician
North York, Ontario
Ray Default
 

What is the problem that you are trying to fix? Is the problem intermittent? Can you list the modules with the codes.

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Mike Technician
Atlanta, Georgia
Mike Default
 

Ray, no codes (odd for a Promaster, I know) I was looking for a draw. The customer was convinced something was killing the battery. I put in a fresh battery and let it sit with my meter hooked up watching for a draw. It did not have one. But whenever I check for a draw, I also will have my scope on the DLC and look for activity on the networks to see if anything is awake. There was none but…

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Matthew Mobile Technician
Bartlett, Illinois
Matthew Default
 

It used to be easier to feel confident in the battery fixing the drain issue when we could actually access the cells for testing lol.

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Mike Technician
Atlanta, Georgia
Mike Default
 

I never went that deep into battery testing myself. But I do still use a carbon pile load tester instead of electronic.

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