Battery low voltage message

[Jpaschal]

I have a 2018 Ram 5500 that the low voltage light keeps popping up constantly and has been for the last 3 months. Batteries are new. Four months old. They both load test at 1000cca. Alternator is new. It was replaced 2 weeks ago. Battery sensor is new. Just replaced today. There are no codes in the ecm. Nothing is indicating there is a problem with the charging system except for the constant annoying DING every ten seconds while the engine is running. There is no corrosion on any wiring. I have even load tested the passenger battery from the driver’s side cables and vice-versa. Batteries still passed load test. Message center on dash will read 13v and still display the low battery message. A volt meter will read 13.7v while driving and still the message will display. There is no reason for me to think there is a problem with the batteries actually charging. The truck can go hours on acc and running my laptop with no problem starting up. What else would cause this message to falsely pop up?

 

[GTyankee]

Just some thoughts

Are you running a Battery Isolator & Fusible Link inline before the Auxiliary Battery ?

What is the Alternator Rating ? 220 ?
What is the rating at idle ? 150 ?

What gauge is the power wiring between batteries ?

 

[Jpaschal]

This is all OEM factory stock.

 

[18CrewDually]

Did this issue start after the alternator replacement or was it the cause for replacement?
I'd monitor all the input voltages, such as PCM, using a scan tool. If the PCM or a module is receiving low voltage then I'd check that wiring circuit and plugs.
Also a "new" alternator out of the box can be bad. If it is not responsive to the commands from the PCM then the PCM will flag it. For example if the PCM is commanding a target voltage of 14.2 but the alternator only puts out 13.4 then it will flag it.

 

[Jpaschal]

The only repair before the message with the constant annoying ‘ding’ was replacement of the batteries. Batteries were replaced about a month before the problem started. Also, I will mention, all replacement parts are Mopar bought from the dealer.

 

[Mister Luck]

The positive battery terminal clamp is capable of distortion if over tightened.

Battery’s themselves can have a bad cell from the factory, although rare it can happen.

If you have not used a scan-tool, write down the codes you find, then clear any codes present or pending.

Check all grounds especially ones that are difficult to reach,
I suggest the grounds and connections below the chassis especially if concealed (for example) by skid plates.

How’s the condition of your serpentine tensioners and did you re check the belt after initial installation of the new alternator?

 

[SitKneelBend]

I have a 2018 Ram 5500 that the low voltage light keeps popping up constantly and has been for the last 3 months. Batteries are new. Four months old. They both load test at 1000cca. Alternator is new. It was replaced 2 weeks ago. Battery sensor is new. Just replaced today. There are no codes in the ecm. Nothing is indicating there is a problem with the charging system except for the constant annoying DING every ten seconds while the engine is running. There is no corrosion on any wiring. I have even load tested the passenger battery from the driver’s side cables and vice-versa. Batteries still passed load test. Message center on dash will read 13v and still display the low battery message. A volt meter will read 13.7v while driving and still the message will display. There is no reason for me to think there is a problem with the batteries actually charging. The truck can go hours on acc and running my laptop with no problem starting up. What else would cause this message to falsely pop up?

I would inspect the factory ground points and possibly clean them up. For the ones in the engine bay, I removed the bolt and ground off the paint to get to clean metal. Then reinstalled and covered the bolt head and ground connection with liquid electrical tape.

There are also ones on the frame that should be looked at. Even if it's not the problem, it won't hurt to improve them.

 

[Jpaschal]

All the grounds have been checked. Nothing was loose or corroded. I’ll reiterate: There are no codes. Drove truck with scanner hooked up. Voltage is between 13.84-13.91 at all speeds. Truck still ‘dings’ and Low battery message. I’m at my ends on this. I’m about to replace the batteries once more and if it still ‘dings’, I’m am going to ice pick the speaker that keeps dinging.

 

[crash68]

Battery sensor is new.

Are you referring to the IBS that's on the negative battery terminal?
I'd double check that the clamp isn't cracked. Also disconnect both grounds then reconnect to put the IBS through a self calibration cycle.

 

[Jpaschal]

IBS is new. It was replaced yesterday. Mopar part. By VIN.
Replaced the batteries again today. No change. At this point I give up. It is a false code. If the alternator is charging at 13.84-13.91V, then there IS no problem as far as I am concerned. I am just going to disable the ‘ding’. I just now have to find it’s speaker.

 

[Mister Luck]

The alternator output does not seem correct,
my output was always 13.8 or 14 but never below.

I realize you have two batteries but it’s commonly ignored both the alternator and battery health are intertwined,
where as a weak battery will overwork an alternator,
and a weak alternator will eventually be the demise of the battery.

An alternator’s job is to maintain a battery not to recharge a battery.

 

[GTyankee]

The Rams brain will not allow the voltage regulator that is built into the alternator to put out a full charge

Batteries straight from the store only have something like a 1/2 charge

I would put a Battery Tender on your primary battery
Make sure the battery tender is the correct type for your particular batteries

 

[18CrewDually]

The alternator output does not seem correct,
my output was always 13.8 or 14 but never below.

I realize you have two batteries but it’s commonly ignored both the alternator and battery health are intertwined,
where as a weak battery will overwork an alternator,
and a weak alternator will eventually be the demise of the battery.

An alternator’s job is to maintain a battery not to recharge a battery.

The PCM controls voltage through pulse width modulation (PWM) of the field wire. Chrysler vehicles have been that way since the early 90s. Most vehicles work like this now. No regulator in the alternator.

I had a truck I worked on today with a battery light that would come on after 10 seconds of running. I monitored all module voltages and the PCM Desired voltage. PCM was trying to regulate to 13.8 but the alternator would put out 14.4 upto 14.8+ volts. The customer had already changed the alternator recently and new battery. Since the alternator wasn't meeting the PCM's desired volts, it set the battery light on the cluster.
I called the parts store (same store the customer got it from) and had them replace the "new" alternator with another one. I swapped them out and it is fixed. Light stays out and now the voltage meets the PCM's desired.
Point is you need a quality scanner that can monitor manufacturer specific inputs. It can get frustrating guessing if you're not sure how the system is supposed to work. And new parts do not mean they're good!
This is why techs get paid.

 

[clifford15]

Just throwing this out there but maybe check if the grid heater is stuck ON…

 

[Mister Luck]

edit

 

[Mister Luck]

The PCM controls voltage through pulse width modulation (PWM) of the field wire. Chrysler vehicles have been that way since the early 90s. Most vehicles work like this now. No regulator in the alternator.


This is why techs get paid.

Good point …
the alternator still needs to generate sufficient voltage to be regulated.

 

[Marshall]

I don't know what a 5500 should put out, I would think that voltage is a bit low, I thought it should be more 14.2 when charging. good luck finding the speaker, or buzzer. with these thing , that could bring up another code.

 

[Devin Meek]

Does your truck have a little sensor coming off the negative terminals? I had a issue like it, replaced battery, alternator and turned out to be a 60$ sensor on the negative terminal

 

[roadrnnr]

you got a pic of that sensor?

 

[SGTrvlr]

I have a 2019 1500 with 5.7 eTorque, all stock with no modifications. Presently has 18,000 miles. This truck has been dinging and showing low voltage at random times since new. It throws no code although the CEL comes on while the low voltage is displaying. When low voltage displays, it displays 14 v. After 15,000 miles it has started randomly displaying “Power Steering Unavailable. Requires service” and the power steering goes out. May last from a few seconds to a minute. This does not throw a code. Take it to dealer and they do nothing because no codes are showing. Report it to Ram cares and they issue a case #. Now this AM the transmission is not shifting, no dings though. Get it up to speed for that gear, shift to neutral, and back to drive and it is in proper gear for that speed. I now have a manual shift! Luckily, I have a Thursday appt with dealer service to replace HVAC module, second in less than 1 month. Not a real happy Ram owner.