Hey everyone looking for some help because we are stumped. I have a 2001 Dodge Ram 2500 Cumminswith a built 47re(shift kit, tq, etc.). For a while it would occasionally throw a no bus code and all dash gauges would die but go away after taking the battery terminalsoff. This week the truck went from 14v to 8v on the highway and got stuck in 3rd gear. Got home and truck started up at 12v. Alternator failed at Advanced Auto so put a new one in. Truck now is sitting at 12V and starts off in 3rd gear. Drives fine when I manually put it in 1st and 2nd gear but in drive its a slug. Can the volts being at 12 cause this? Has anyone ever experienced this before or think they know what could be the cause? I have cleaned all the grounds and they all have checked good with a multimeter. Im stumped any help is appreciated, thanks!

 

Check the main power terminal nut at the pdc under the hood. Also, just because the alternator is new, dont automatically rule it out.

 

Took the alternator to get tested and it was fine. Put it back in and still at 12volts with limp mode. Wheres the nut you are talking about?

 

Did you check the batteries? If one of the batteries is bad then it can cause all kinds of weird problems. Completely disconnect both batteries from each other and the truck and test their voltage separately. If they're in good shape then you'll see 12.6 volts. DONT test them connected to each other. If they're good but not brand new then you'll see 12.5 each. Anything less is unacceptable and they need to be replaced as a pair. Do NOT replace one and not the other as dual batteries will drag each other down and cause electrical anomalies. You can have them load tested but typically their static voltage will tell you all you need to know. That said, dont charge them before testing and dont test them right after a charge. They need to sit for about an hour before checking otherwise you'll get a false reading.

Then check the alternator for AC voltage. Not DC but AC. You can do this with a regular multimeter that reads in both AC and DC. Switch to DC and set the voltage to 200. Touch the red lead to the alternator main output on the back and the black lead to the alternator housing itself, not the battery ground. If the AC voltage is more than .050 then you're going to cause the sensitive electrical components, like the ECM, PCM, PSG, and trans solenoid, to be affected and possibly damaged over time.

 

Thanks Katoom for the response. The passenger side battery was venting a lot of fluid before the alternator went. I got it load tested assuming it was shot and they said it passed with good cca and volts. The drivers side sits at 12.6 but i didn't have it load tested. The new alternator was also just tested at advanced and passed. I will take the drivers side battery to get tested thanks.

 

I'd test the truck with just the drivers side battery connected.

Remove both grounds from both batteries.

Disconnect the red cable that connects the batteries on both sides, insulate properly.

Test drive. If OK, you know that your passenger side battery is dragging down the system.

If not OK, swap the batteries, test again with just one battery.
If OK, you know your original drivers side battery is bad.

If not, look elsewhere...

HTH

 

If the battery tested OK then thats good but usually excess venting means it was overcharging a lot. I'm not a fan of the parts store techs either since they often have very little knowledge and tend to botch things up. Also, I have yet to hear of a parts store who tests for AC voltage. They'll make sure the DC voltage is correct but wont test AC voltage. Only specific alternator shops will bother with checking. The better alternators which use 12 diodes and hairpin wiring will produce the least amount of AC voltage too.

In all fairness AC voltage is typically not a problem on most vehicles but because Dodge ran the ground wire the way they did in front of the motor along with all the other wires, the entire electrical system on these trucks is very sensitive to any AC voltage over .050. There's even writeups on how to reroute the ground and add another ground source to eliminate the problem, especially since its a well known problem for AC voltage to affect trucks with automatic transmissions and cause rapid on/off cycling of the torque converter.

 

Thanks for the response guys. Im going to look into it as best I can. I have a friend of a friend who does extensive electrical testing for a good price. I honestly don’t have the time with work to really get in there. Ill keep you guys updated!

 

Maybe check the transmission sensors or torque converter.