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Help with CAN B Values when key on engine off. (Not CAN C)

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2 years 5 months ago #52111 by hacerz
-> can anyone who knows CAN Bus diagnosis reply to this part, My can B- (Not Can C) show almost battery voltage(0.5 less may be) and Can B+ shows 0.5v on key off.
But on Key ON Engine Off, B- shows 4.5v and B+ shows .5v. Is this considered B- short to 5v reference? I am not sure if CAN B values are also same as CAN C (eg: 2.7 on low and 2.3 on High to make it 5v)

Intermittent stalling on stops when giving gas. Mostly seems to be when stopping harder than usual on red lights and then starting. fuel trims are -4 to -5 on both trims. and short trims going to 15 to -15 when giving gas and releasing. but long term its -4 to -5. so its dropping hard negative when hard stopping and no fuel pressure in return? (My best guess)

Dodge Magnum RT v8 5.7ltr Hemi 



 

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2 years 5 months ago #52152 by Cheryl
Not sure about can b but are you having communication issues with any modules?

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2 years 5 months ago #52153 by Cheryl
But I’ll check all data tomorrow see if I can find anything on normal Voltage

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2 years 5 months ago #52157 by hacerz
No light per say except, B223D OCM DTC, Not sure what exactly is stored in OCM. Need more advanced scanner I suppose. I have orc scanner but not much detail on this code.

I am getting negative fuel trims -4, -5 and short term jumping from +15 to -15 when giving gas, checked it while idle. Need to see while driving too.

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2 years 5 months ago - 2 years 5 months ago #52158 by juergen.scholl

-> can anyone who knows CAN Bus diagnosis reply to this part, My can B- (Not Can C) show almost battery voltage(0.5 less may be) and Can B+ shows 0.5v on key off.
But on Key ON Engine Off, B- shows 4.5v and B+ shows .5v. Is this considered B- short to 5v reference? I am not sure if CAN B values are also same as CAN C (eg: 2.7 on low and 2.3 on High to make it 5v)



Dodge Magnum RT v8 5.7ltr Hemi 






 
CAN B voltage levels are different from CAN C. There isn´t one unique standard, you will have to look up the specific service information. I attached a picture from Mercedes which outlines  possible variations. 

 

An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
Last edit: 2 years 5 months ago by juergen.scholl.

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2 years 5 months ago #52169 by hacerz
I am getting long fuel trims as -4, -6 appx, I used to get in positive and also the mileage was almost 11mpg and now 8mpg.

I did a idle accelerate and decelerate test, the short term fuel trim jumps to like +15 to +20 and then goes to -20 and also at that moment long trim go -7 to -9 ,

I am guessing a fuel cut? I took a screenshot below,

 
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