Duramax Diesels Forum Truck of the Week
  #16  
Old 11-04-2019, 08:09 AM
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DAVe3283 DAVe3283 is offline
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If that doesn't solve it, one thing I thought of while reading through might be worth investigating. You say it only happens while accelerating while towing. That would mean a very high engine load, which could cause the engine to torque to the side if motor mounts are getting weak/torn. This could in turn pull on the wire harness and cause an intermittent fault. So it may be worth checking if your motor mounts are bad.
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Old 11-04-2019, 07:34 PM
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Originally Posted by db131994 View Post
Well, I may have found the issue... Long story, but it's needed for the background. Last weekend we were camping and had an issue with our converter not charging the battery. When we got home, I went to start troubleshooting the converter issue, and it was magically running (it was not working before and drained the trailer battery). Digging into it, I found a cracked solder joint on the board in the converter. I re-soldered it and all is well with the converter.

We made a trip this weekend, and didn't have the transmission limp issue. I won't say it's "solved" yet, but this may lend to your advice about an issue in the 12V system. My theory is the short in the converter could have been causing volt / amp fluctuations and the communication issue. My trans guy said has seen trailer electrical issues back feeding to the truck causing similar issues.

Until we get a few trips under our belts without issues, I won't say all is well. I did lean on it pretty hard to push the conditions where it caused the trans limp issue before, and it survived...
Hoping you got it sorted out, but I'm left wondering. Assuming you're talking about a normal RV converter which converts AC line voltage to 12v DC to run the house lights, 12v appliances, and charge the house batteries? If so, this unit wouldn't be powered up while you're driving down the road so I can't really think of how that would be a cause.

With '03 OEM wiring, the 12v circuit that feeds the 7 way trailer connector comes from the 40A "Stud 1" fuse which connects directly to the truck battery. Standard setup is that this pin in the trailer connector will be wired directly to the house batteries on RVs, providing ability to charge them while traveling.

Hope it stays fixed.
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Old 11-04-2019, 07:35 PM
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Originally Posted by DAVe3283 View Post
If that doesn't solve it, one thing I thought of while reading through might be worth investigating. You say it only happens while accelerating while towing. That would mean a very high engine load, which could cause the engine to torque to the side if motor mounts are getting weak/torn. This could in turn pull on the wire harness and cause an intermittent fault. So it may be worth checking if your motor mounts are bad.
Really good idea, something to check out.
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Old 11-05-2019, 05:30 AM
db131994 db131994 is offline
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I don't disagree, like I said, until we get a few more trips under our belt I'm not convinced...

Going down the road, the frige is still drawing 12V power from the battery, and the converter is still in that loop. Could capacitors on the converter board cause power fluctuations back through the truck, due to a short?
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Old 11-05-2019, 08:06 PM
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I don't disagree, like I said, until we get a few more trips under our belt I'm not convinced...

Going down the road, the fridge is still drawing 12V power from the battery, and the converter is still in that loop. Could capacitors on the converter board cause power fluctuations back through the truck, due to a short?
True, the fridge will draw on the 12v going down the road. Most modern Dometic or Norcold units only operate the main cooling function on 120v AC or propane, and the 12v is only needed for the fridge control circuitry and it's a pretty low draw though.

The RV converters I'm familiar with bus the 12v RV battery (or batteries), the 12v charge circuit from the tow vehicle 7-way connector, and the RV converter 12-14v charging outputs all together. Then the 12v fused branch circuits for appliances inside the RV are fed from that. Since you mentioned you had a cracked solder joint, without knowing specifics it could be possible that a continuously flaky connect/disconnect situation (road vibration) internal to the RV converter, to a high current load like depleted RV batteries could cause electrical noise on the 12v charge wire from the truck, yes.
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