Ram 2009 Cummins - voltage fluctuation

[Jon71]

Hello -

I have a 2009 Ram 3500 6.7 Cummins. Recently I noticed a “flashing”, lights dim and then back to normal. This cycles on and off for between 2-20 minutes. The voltage change is noticeable in the exterior lights, dash lights, dome lights, hand held voltmeter etc. When I turn the engine off and then back on it stops. It may come back in a few minutes or hours.

I’ve had the alternator changed but that didn’t help. Then we suspected the relay for the engine heater matrix (the pre-heater for the throttle body?) but that didn’t help. While it’s been happening I’ve opened the fuse box and pulled each fuse individually and nothing changed.

I’m hoping someone here has run across this in the past.

Thanks in advance for your help!

Jon

 

[Fast69Mopar]

Hello -

I have a 2009 Ram 3500 6.7 Cummins. Recently I noticed a “flashing”, lights dim and then back to normal. This cycles on and off for between 2-20 minutes. The voltage change is noticeable in the exterior lights, dash lights, dome lights, hand held voltmeter etc. When I turn the engine off and then back on it stops. It may come back in a few minutes or hours.

I’ve had the alternator changed but that didn’t help. Then we suspected the relay for the engine heater matrix (the pre-heater for the throttle body?) but that didn’t help. While it’s been happening I’ve opened the fuse box and pulled each fuse individually and nothing changed.

I’m hoping someone here has run across this in the past.

Thanks in advance for your help!

Jon

What condition are the batteries in?

How old are the batteries?

Have you checked the cable that connects both batteries together for corrosion?

Have you tried disconnecting the grid heater and running the engine to see what happens to the system voltage?

 

[crash68]

It's most likely the grid heater causing the lights to "flicker" and as mentioned above it's probably aging batteries. The grid heater draws a lot of amps and can cycle anytime the engine is not up to operating temperature. It's possible the IBS(sensor on negative terminal) is starting to malfunction.

 

[Jon71]

Thank you for your replies!

Fast69Mopar -

What condition are the batteries in? Tested and good

How old are the batteries? Less than 2 years

Have you checked the cable that connects both batteries together for corrosion? No, I will take a look in the morning.

Have you tried disconnecting the grid heater and running the engine to see what happens to the system voltage? Yes. I drove it for 2 days with the positive cable for it disconnected. No change unfortunately.

Crash68 -

Was is the IBS you are referring to? What does it do?

Thanks for so much your suggestions!!

Jon

 

[crash68]

Was is the IBS you are referring to? What does it do?

Basically it feeds back the state of the battery charge to the ECM so the vehicle can control the alternator. I posted a link here for a more complete description:
https://www.ramforum.com/threads/low-battery-but-no-symptoms.156851/#post-2215041

 

[Southern Beard]

I am having the same issues on my Cummins. The truck has been fully deleted, and I have noticed that there is no IBS sensor anywhere. Batteries are good.
Connections and grounds are good
I'm still getting random voltage fluctuations ranging from about .3 to .8 volts.
Any other parts or things I could check before I just set my truck on fire

 

[Corey_lax]

I am having the same issues on my Cummins. The truck has been fully deleted, and I have noticed that there is no IBS sensor anywhere. Batteries are good.
Connections and grounds are good
I'm still getting random voltage fluctuations ranging from about .3 to .8 volts.
Any other parts or things I could check before I just set my truck on fire

Have you came up with a solution to this? I have a generator low voltage code P063c. Battery light comes on and off while driving but didn't notice anything weird driving like this for a year until driving home late last night with no headlights, only fog lights. My battery and alternator are 6 months old and no change to the symptoms. I monitor the voltage on my Bullydog tuner and it's always around 13.9-14.1