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

[LouM]

What would be nice is an INEXPENSIVE method to have a fast idle that would only work in Park or Neutral.

 

[RamDiver]

What would be nice is an INEXPENSIVE method to have a fast idle that would only work in Park or Neutral.

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[Docwagon1776]

Doesn't surprise me. As mentioned by several people it was probably just a dead battery.
Looking at the alternator output curves even the big 220A optional alternator is probably only putting out 15 amps max at idle. Even with big dual batteries the reserve capacity at 25 amps of those is only a few hours. Between having the AC on, fan cranked, other electrical draw....and maybe some subpar batteries it's quite feasible that you are just slowly draining the batteries.

Alternator rpm is not 1:1 with engine rpm, though. Pulley size difference will make it spin faster than the engine crank, generally something in the low 2.X range. Cars are designed to run the accessories at idle with no issue.

There's a decent aftermarket for underdrive pulley sizes that alter the ratio, at least for Camaros and Corvettes, to reduce the parasitic drag.

 

[knightwe]

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.

That’s what I was thinking. The engine powers the AC compressor through a belt. The only thing that needs power in the AC/heat is the heater fan. Even a lot of cars use vacuum to control the vents.

 

[nuckinfutz]

What would be nice is an INEXPENSIVE method to have a fast idle that would only work in Park or Neutral.

There is...at least on my 2017 3500. It does say "engage the parking brake", but I've never had to do that.

"To enable high idle on a 2017 3500, engage the parking brake, turn on the cruise control, and then press the "Set" button to reach a predetermined engine RPM, such as 1000 or 1200 RPM. Deactivating high idle can be done by pressing the brake pedal, releasing the parking brake, tapping the cruise control "Set" button, or turning the cruise control off."

 

[NMMustangg]

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.

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I appreciate all the conversation about Batteries and Alternator but as I said in my original post, The batteries are both good, both charged, it's not a starting issue, the Dash is completely dead, including the keyless start (button) so I can't get in even into Accessory to use the computer to run diag thru OBDII with computer using AlphaOBD.

Batteries are full charge, i do have auxiliary battery charger/jump start (big one) has no effect.

Power as far as lights work when Batteries are connected but dead dash still

 

[LouM]

Have you checked the big bolt on master fuses?

 

[LouM]

Or power to all the fuses and relays?

 

[dodge daddy]

wow, 200A for the a/c? i think its a 10 amp fuse for the clutch, and maybe a 15A for the blower motor.

 

[RamDiver]

I appreciate all the conversation about Batteries and Alternator but as I said in my original post, The batteries are both good, both charged, it's not a starting issue, the Dash is completely dead, including the keyless start (button) so I can't get in even into Accessory to use the computer to run diag thru OBDII with computer using AlphaOBD.

Batteries are full charge, i do have auxiliary battery charger/jump start (big one) has no effect.

Power as far as lights work when Batteries are connected but dead dash still

While you may have information about the batteries' health, you haven't yet shared those details.

Please consider that we encounter this same scenario multiple times per day, and have a standard operating procedure (SOP) for a reason.

Our trucks are rolling microcomputers, and the behaviour can very often be unusual and not very intuitive to resolve faults.

The SOP while troubleshooting any computerized device is usually the same.
Start with the most common shared resource, the B+.

There are two different types of battery status in the troubleshooting world: tested or untested.
The condition of a new battery or batteries is unknown, and irrelevant if they are untested.

Also, the digital battery load testers used in most commercial establishments are prone to false positives. A flakey cell will not be apparent without a significant load, ergo the toaster-style battery load tester from HarbourFreight.

To be perfectly honest, I believe the fault lies elsewhere, but the SOP removes all doubt and prevents us all from wasting time and effort only to be bitten in the a$$ long afterwards by a bad cell.

The toaster-style battery load tester from HarbourFrieght costs $18 and will provide definitive proof of the batteries' status, whether they are new or otherwise.

I like Lou's suggestion of checking the bolt-on fuses, but I know on my truck, they only serve a couple of high-current devices, such as the starter motor. The values on my truck are 120A & 180A.



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[62Blazer]

Alternator rpm is not 1:1 with engine rpm, though. Pulley size difference will make it spin faster than the engine crank, generally something in the low 2.X range. Cars are designed to run the accessories at idle with no issue.

There's a decent aftermarket for underdrive pulley sizes that alter the ratio, at least for Camaros and Corvettes, to reduce the parasitic drag.

Yes, you are correct. I replied back to my post last week with a correction to my statement.

 

[ginokaan]

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!

Check PCM After BCM to Tranny. The problem is there. I’m %100 sure.