Electrical headache, please help!!
06-25-2012, 12:03 PM
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Electrical headache, please help!!
I have a 1996 Ram with 12v cummins, the alternator wont charge, I have no tach, cannot read codes, no speedo etc. I tested the voltage going into the pcm and that was good but then i tested the voltage out of the pcm and discovered it only had a 0.78v reference rather than the full 5v. It sounded like it could be a pcm problem so the first thing i did was beef up the pcm ground right from the battery. This did nothing, next i tried unplugging just about everything that could use that 5v reference hoping to find a sensor that was shorting the 5v reference. I have found nothing, with everything unplugged it still has the 0.78v reading. I was convinced that this was a pcm problem. I was lucky enough that my local auto wrecker had a used guaranteed pcm so i picked it up and installed it. Nothing changed after installed!! I'm lost on what to do next, im thinking that the used pcm is not functioning right but they assured me that the tested it before the truck was dismantled..
06-25-2012, 03:38 PM
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Does the "new" pcm also put out 0.78 volts? If the output is just the same, I'd look for more troubles in teh truck, but I'd also get a new pcm ordered. It could be they only garunteed that it was a pcm out of a truck like yours, right down to the electrical glitches...
06-25-2012, 05:37 PM
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I have a 1996 Ram with 12v cummins, the alternator wont charge, I have no tach, cannot read codes, no speedo etc. I tested the voltage going into the pcm and that was good but then i tested the voltage out of the pcm and discovered it only had a 0.78v reference rather than the full 5v. It sounded like it could be a pcm problem so the first thing i did was beef up the pcm ground right from the battery. This did nothing, next i tried unplugging just about everything that could use that 5v reference hoping to find a sensor that was shorting the 5v reference. I have found nothing, with everything unplugged it still has the 0.78v reading. I was convinced that this was a pcm problem. I was lucky enough that my local auto wrecker had a used guaranteed pcm so i picked it up and installed it. Nothing changed after installed!! I'm lost on what to do next, im thinking that the used pcm is not functioning right but they assured me that the tested it before the truck was dismantled..
Start with fuse 9, 10 amp in dash, verify it is good, runs thru ASD relay to C3 on PCM connector C3. Fuse 4 ( 30 amp ) ind PDC runs thru ASD relay to C12 on PCM conn. C3 ( this is ASD relay sense )
Your ESS sensor ( which is probably why you don't have Tach, charge, etc....) Gets it's supply voltage from pin A17 on connC1 and returns the signal to pin A8 on C1.
This gets very confusing, your best bet would be to order a Factory Service Manual from Genos garage for your particular year, it literally is the best money I ever spent, 35 bucks gets you a legit licensed copy on CD.
http://www.genosgarage.com/1996-DODG...nfo/DFSM96_CD/
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