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2016 Ram 3500 Longhorn - Battery Drains Overnight, No Codes

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Mike T. · rep 0 · May 25, 2:26 AM · 1 replies · solved · Question

Vehicle: 2016 Ram 3500 Longhorn

Hey guys,

I'm pulling my hair out with my 2016 Ram 3500 Longhorn (6.7L Cummins). For the past few weeks, the battery keeps dying overnight. I've had both batteries (it's a dual battery setup) tested, and they're good. The alternator was also checked and is charging properly. I even replaced both batteries just in case, and the problem persists.

There are no check engine lights or any other warnings on the dash, and my scanner isn't pulling any codes. It's incredibly frustrating to wake up to a dead truck, especially when I need it for work. I don't have many aftermarket accessories, just a dash cam that's hardwired but turns off with the ignition.

Has anyone dealt with a parasitic draw on their Ram? What's the best way to track down what's draining the power? Any common culprits on these trucks?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:26 AM

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ClearTheCode admin answer: A parasitic battery drain on your 2016 Ram 3500 Longhorn, especially with healthy batteries and alternator, indicates something is drawing power when the truck is off. This can be tricky to diagnose without specific codes. Here's how to approach it:

  1. Perform a Parasitic Draw Test:

    • Method: This is the most effective way to find the culprit. Disconnect the negative battery terminal and connect a multimeter in series between the negative battery post and the negative battery cable (set to amperage measurement). Close all doors, turn off all accessories, and let the truck 'go to sleep' (this can take 15-30 minutes as modules power down). A normal draw should be around 20-50 milliamps (0.02-0.05 amps). If it's significantly higher, you have a draw.

  2. Isolate the Circuit:

    • Method: Once you confirm a parasitic draw, start pulling fuses one by one from the fuse box (both under the hood and inside the cabin) while monitoring the multimeter. When the amperage drops significantly, you've found the circuit responsible. This narrows down the components to inspect.

  3. Common Ram Parasitic Draw Culprits:

    • Radio/Uconnect Module: These can sometimes stay awake or malfunction, causing a drain. Try pulling the fuse for the radio/infotainment system.
    • Body Control Module (BCM): A faulty BCM can fail to properly shut down other modules or itself, leading to a drain. This is less common but possible.
    • Aftermarket Accessories: Even if your dash cam is supposed to turn off, double-check its wiring. Any aftermarket alarm, remote start, or lighting could also be a source.
    • Alternator Diode Failure: Although your alternator tested good, a failing diode can sometimes cause a slight internal drain. This is less common if the charging system is otherwise healthy.
    • Trailer Brake Controller/Tow Package Wiring: Issues with the trailer brake controller or wiring to the trailer plug can sometimes cause a draw.

When to See a Shop: If you're uncomfortable performing electrical tests, or if you've pulled all accessible fuses and still can't find the source of the draw, it's time to take your truck to a qualified automotive electrician or dealership. They have advanced diagnostic tools and experience tracing complex electrical issues that may involve internal module failures or hidden wiring problems.

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