2018 Ram 3500 Laramie 4 wheel drive long bed 6 l diesel with dead dash won't start batteries good

[NMMustangg]

2018 Ram 3500 Laramie crew cab long bed 6.7 l Cummins

I'm hoping somebody has an idea to help.

I had pulled over in a truck stop left the truck idling with AC on while I crashed a little while. Woke up to the dash being off, the wipers going and the truck would not shut off.

I finally had to pull one of the relays under the hood to get this truck to shut down and it has been dead ever since

I ohmed out every single fuse and swapped out every relay in the TIPM (PWR Distribution)

I even completely unplugged TIPM, took it out, blew out and made sure it was completely clean before putting it back in.

No power to OBDII in order to run diagnostic AlfaOBD on it to pull codes.

I've never had any problems even the smallest with this truck and I've owned it since it was virtually brand new.

Anyone have any ideas?

I know the RF receiver might be involved but I haven't found a way to test it, another is possibility of it being Body Control Module, again don't know a way to test it other than going through the OBDII port

I have pretty much run out of ideas and of course no warranty left on the truck even extended warranty so everything's out of my pocket that's why I haven't taken it to the dealer shop

If you have any information please let me know here and you can also send me an email at [email protected] if that's easier.

Really grateful for any help I could get guys!

 

[Burla]

How old is the battery/.

Alt has a hard time charging at idle with AC on.

 

[Ritchie_Rich]

Sounds like weak batteries. Or alternator. The alternator should put out plenty of juice to charge the batteries at idle with the a/c on.

 

[Burla]

You can drain a car battery in 1/2 hour to 2 hours by leaving headlights on while car off, and that is less the 10 amps to run that item. A truck AC can take up to 200 amps, maybe a little less. The system of gears is designed to have peak amperage from alt at between 1300 and 2000 rpm's by vehicle. Even with two batteries w/o alt it wouldn't take long to drain battery. Now at 800 idle rpm's it is not charging 200 amps to keep up with that draw. Add the possibility of an aging battery in a state with a low average lifespan on a battery life, this makes a lot of sense?

Just ask your Google you see alt generates a range of "An alternator at idle can produce anywhere from 5 to 50 amps, with output depending on the car's electrical load."

So if it was healthy Cummins battery and alt, I can see an hour of AC no issue, but if the battery is even a couple years old in NM it is easy to suspect battery. Average battery life can be less the 4 years there, so the question remains, how old is battery.

 

[Ritchie_Rich]

You can drain a car battery in 1/2 hour to 2 hours by leaving headlights on while car off, and that is less the 10 amps to run that item. A truck AC can take up to 200 amps, maybe a little less. The system of gears is designed to have peak amperage from alt at between 1300 and 2000 rpm's by vehicle. Even with two batteries w/o alt it wouldn't take long to drain battery. Now at 800 idle rpm's it is not charging 200 amps to keep up with that draw. Add the possibility of an aging battery in a state with a low average lifespan on a battery life, this makes a lot of sense?

Just ask your Google you see alt generates a range of "An alternator at idle can produce anywhere from 5 to 50 amps, with output depending on the car's electrical load."

So if it was healthy Cummins battery and alt, I can see an hour of AC no issue, but if the battery is even a couple years old in NM it is easy to suspect battery. Average battery life can be less the 4 years there, so the question remains, how old is battery.

View attachment 571967

OMG! 200 amps? HAHAHA
Check your fuse box. It’ll have a 30-35 amp fuse in the a/c slot.
Not 200a.
BTW, I grew up in southern MM. And I now live in southern AZ. My batteries last 5-6 years at least.
Google isn’t a know-it- all.

 

[Docwagon1776]

You can drain a car battery in 1/2 hour to 2 hours by leaving headlights on while car off, and that is less the 10 amps to run that item. A truck AC can take up to 200 amps, maybe a little less.

No way a truck AC is drawing that much power. A good sized refrigerated straight truck unit doesn't even draw 30, and that's keeping a bigger area of a truck below freezing.

*edit* JFC, R-E-E-F-E-R is censored here.

 

[62Blazer]

The initial issue really sounds like a low voltage issue. Have you actually checked the battery? Did you try jumping it? Keep in mind that if a battery is completely toast you may not even be able to jump it. I have a diesel with dual batteries and went through this a couple of times. A big jump pack would barely even crank the engine over, and hooking up jumper cables to another truck with a decent size battery and alternator while revving it up wouldn't even crank it fast enough to start. Put good batteries in it and it cranked right up.

 

[Burla]

No way a truck AC is drawing that much power. A good sized refrigerated straight truck unit doesn't even draw 30, and that's keeping a bigger area of a truck below freezing.

*edit* JFC, R-E-E-F-E-R is censored here.

The engine supplies most of the draw, the fuse or relay obviously couldn't supply all the power it takes to run an AC, which is why it doesn't. I don't know the amps, but it's a lot. Thus why you lose up to 10% of each gallon of gas when it's running.

 

[mtnrider]

Did you load test the batteries? Measuring the voltage is not a good test for a bad cell. You have all the symptoms of one and 99% of the time these no start situations like this are a bad battery. They don't go slowly, they work one minute and won't start the next. If you are getting 5+ years out of them you are Way above the curve. Typical is 3 years in these trucks. (first hand experience, not google)

I've seen this 100 times, people start throwing parts at the truck before doing the most basic troubleshooting.


.

 

[Burla]

OMG! 200 amps? HAHAHA
Check your fuse box. It’ll have a 30-35 amp fuse in the a/c slot.
Not 200a.
BTW, I grew up in southern MM. And I now live in southern AZ. My batteries last 5-6 years at least.
Google isn’t a know-it- all.

The problem being the fuse box doesnt supply the power here.

 

[Burla]

"Capiche"

 

[Docwagon1776]

The engine supplies most of the draw, the fuse or relay obviously couldn't supply all the power it takes to run an AC, which is why it doesn't. I don't know the amps, but it's a lot. Thus why you lose up to 10% of each gallon of gas when it's running.

What the belt is mechanically driving is completely irrelevant to the notion the truck is going to drain the battery by idling with the AC on. The electrical system component is all that matters there, and that's much more likely to be 20 amp than 200 amp.

 

[Burla]

What the belt is mechanically driving is completely irrelevant to the notion the truck is going to drain the battery by idling with the AC on. The electrical system component is all that matters there, and that's much more likely to be 20 amp than 200 amp.

Not irrelevant, but rather going off into the minutia of an AC draining a battery at idle, it is a good place for the OP to start. ECM only makes small adjustment at idle, the battery assist comes in to help the engine. Keep in mind it is such a high draw that the ECM is designed to compensate for it, or the engine would stall on the spot.

I wont comment further, we can agree to disagree on this one.

In a gasoline-powered car, the battery assists the engine by providing the initial high-power jolt to start the combustion process. The battery works harder when the A/C is on at idle because the alternator, which normally powers the car's electrical systems, is spinning slowly and producing less power. The battery must then supplement the alternator's output to meet the higher electrical demand

 

[Docwagon1776]

In a gasoline-powered car, the battery assists the engine by providing the initial high-power jolt to start the combustion process. The battery works harder when the A/C is on at idle because the alternator, which normally powers the car's electrical systems, is spinning slowly and producing less power. The battery must then supplement the alternator's output to meet the higher electrical demand

Is that some AI nonsense?

The battery neither knows nor cares what the crank is driving mechanically, it only knows what the draw is on the electrical system. I could run a PTO off the crank and it has nothing to do with the battery.

If a vehicle at idle didn't produce enough electricity to run the AC, there would be a lot more dead vehicles. Police and EMS fleets idle constantly and run a hell of a lot more electrical doodads than just the AC, and they aren't getting massive alternator upgrades these days. I'm sure there are a ton of users who car/van camp or leave animals in the vehicle or whatever and let the vehicle idle for long periods of time with the AC. Nobody comes back to a dead battery as a result.

 

[Ritchie_Rich]

The problem being the fuse box doesnt supply the power here.

Sure it does. Every thing goes through a fuse of some sort. That’s the only way to protect the electrical system. There will be a fuse for the compressor circuit and one for the blower motor circuit. Probably one for the electronic dash a/c controls as well. Stop believing AI.

 

[Ritchie_Rich]

"Capiche"

Don’t know where you’re going with that???

 

[Burla]

\

Don’t know where you’re going with that???

No problem, I can help you with that. Notice the pulley, that is what supplies the lion share of the power to run that item. That is a ram A/C compressor mostly powered by the pulley not going through a relay. That item takes about 2 gallons of fuel to run per tank, good luck converting that to amps, it's complicated. Now if that battery is the original battery, or in the case 2, from 2017 when the batteries were put in a 2018 ram that lives in new mexico, then there is very little chance this issue isn't the battery.

Plus the electrical draw from clutches and blowers, etc. Those do go through relay.

 

[RamDiver]

I believe that both of you have mentioned valid points, but not knowing the condition of the batteries likely has some relevance.

I suspect that more recently designed alternators, together with modern-day ECM/PCMs, would tend to improve the available alternator current draw at idle.

Browsing various sites, I have the impression that a functional HD alternator should be able to handle the HVAC load at idle speed.

The attached HD 220A alternator specs show 111A at 1500 rpm @200°F or 133A at 1500 rpm @75°F. That 1500 rpm is not the engine but the alternator speed, AFAIK.

From looking here and there, the alternator speed is dependent on pulley size, but is often about double the engine rpm.

Also, doesn't the ECM/PCM have the brains and ability to idle up the engine during a higher current load condition?


The SOP for any potentially power-related fault is always the same: load test the batteries with a toaster-style battery load tester. Always replace dual batteries as a pair, regardless of whether one looks OK.

I'll include the entire page of load testers here because the link to the $18 unit at HarbourFreight has recently been hit or miss daily.

.

 

[Docwagon1776]

\

No problem, I can help you with that. Notice the pulley, that is what supplies the lion share of the power to run that item. That is a ram A/C compressor mostly powered by the pulley not going through a relay.

Which means it's irrelevant to the alternator and battery. Unless you believe the water pump somehow draws from the battery and alternator as well, same thing.

 

[Burla]

Which means it's irrelevant to the alternator and battery. Unless you believe the water pump somehow draws from the battery and alternator as well, same thing.

With respect, he asked me a question on an item before I said I wasn't going to comment, so I respectfully explained the pic.

A= W / V, thus in a 12v system. Example- 100-watt bulb in a 12-volt system will draw 8.3 amps. Now compare that to what it takes to run an AC a compressor versus how much power an alt can generate at idle. Its science.