Dodge Challenger Forum banner

1 - 20 of 25 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
I have a 2016 Scat Pack with about 9400 miles that I picked up about 2 weeks ago. I noticed the headlights were flickering and the dash was flickering. I started watching voltage on the dash and it’s all over the place

Seems stable at startup but gets silly a little later. I completely disconnected the amp and get the same.

Took voltage measurements under hood and at the battery in the trunk at idle and got about 14.25v under hood and about 13.15v in the trunk.

I’m not liking that voltage drop and I’m really not liking the instability of the voltage even while driving

I know there were issues with her earlier alternators, but I haven’t seen anything saying this should be impacted. Is this normal?

986536


986537


here’s a video of the voltage while driving:
 

·
Registered
Joined
·
1,904 Posts
Used car. Because you can't know what the previous owner might have done you have to carefully check for any loose connections between the battery and the alternator and the alternator and other places.

If anything electric and aftermarket has been installed start there.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #3
Used car. Because you can't know what the previous owner might have done you have to carefully check for any loose connections between the battery and the alternator and the alternator and other places.

If anything electric and aftermarket has been installed start there.
I’ve checked everything I can see right now, completely disconnected the stereo amp and reseated the battery terminals. I also checked under hood voltage using the both the engine and the chassis as grounds with no difference in voltage.

Other than that everything seems tight. This is driving me a little nuts
 

·
Premium Member
Joined
·
5,328 Posts
So the Underhood was higher than at the battery? That shouldn’t be too hard to narrow down then. Start at the battery and work your way forward in testing voltage while running. Somewhere it should jump up when the dropped voltage is no longer being dropped from the circuit. Zero in on that section of the wiring system and find the culprit.
 

·
Premium Member
Joined
·
5,328 Posts
You did test the posts and cables connecting at the posts on battery, correct? If not, do that first and make sure the voltages are the same (13.x).
 

·
Registered
Joined
·
8 Posts
Discussion Starter #6
So the Underhood was higher than at the battery? That shouldn’t be too hard to narrow down then. Start at the battery and work your way forward in testing voltage while running. Somewhere it should jump up when the dropped voltage is no longer being dropped from the circuit. Zero in on that section of the wiring system and find the culprit.
That’s next on the list. It should be a pretty straight shot from the large battery lug under the hood where I measured the voltage there to the battery in the trunk, however I’m going have to figure out how it’s routed and start looking from there

I do wish I knew what the normal voltage drop is between these points and if it’s a straight shot or not
 

·
Registered
Joined
·
8 Posts
Discussion Starter #7
You did test the posts and cables connecting at the posts on battery, correct? If not, do that first and make sure the voltages are the same (13.x).
Yeah, that’s the first picture and I’ve reseated the leads as well on the positive and negative posts
 

·
Registered
2018 Scat Pack SHAKER in Plum Crazy
Joined
·
1,182 Posts
The voltage readings at the front vs the rear are really probably meaningless. With it fluctuation like that, both are in the range that the dash indicates. I would suspect it is regulator related, but I'm not sure. What I would do is look up the fuse list, and start pulling fuses for things that don't affect the engine. If it stabilizes when one is pulled, that may be a good indication of where to look.
But first, any warranty on it?
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,172 Posts
Wiring diagrams and images of how cables and harnesses can be found here:
 

·
Premium Member
2014 100th Annivesary R/T
Joined
·
517 Posts
1 of 4 things, I would start with grounds first (this is typically the single most cause of all electrical issues), then alternator, then battery, then ECU (ECU manages voltage regulator for the alternator).

Good luck.
-Kenny
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,172 Posts
If anything, I would expect a slight voltage drop when testing the 12V supply up front as it is fed from a long cable that runs from the back to the front. Could be a bad intelligent battery sensor (connects to the negative side of the battery) which tells the PCM state of charge.
 

·
Registered
2019 Challenger R/T Scat Pack Widebody
Joined
·
58 Posts
Not meaning to show my ignorance on the topic just trying to help, has anyone watched there Voltage gauge while driving their car and is the video Erich posted unusual?

As voltage is not something I consider a gauge I would use regularly I can confess I have not driven my car while watching the voltage gauge so I don't know if this is normal or unusual. I would expect that while driving there are voltage fluctuations and probably many per second depending on demand from the electrical system, charging from the alternator and then some so a voltage gauge bouncing between say 13.9v and 14.7v as I think I saw in the video might seem normal to the average person.

I know that doesn't explain the light flickering, sorry.
 

·
Premium Member
Joined
·
5,328 Posts
That’s next on the list. It should be a pretty straight shot from the large battery lug under the hood where I measured the voltage there to the battery in the trunk, however I’m going have to figure out how it’s routed and start looking from there

I do wish I knew what the normal voltage drop is between these points and if it’s a straight shot or not
the B+ wire from the alt goes through the firewall at a lug below the CAF on my car, I suspect it does the same on yours. From the lug in the firewall, it travels along the floor pan on the passenger side up under the rear seat and to the battery positive post and then to the rear PDC.

There should not be a 1V drop between the front posts and the battery, unless one of the grounds has exceedingly high resistance.
 

·
Premium Member
Joined
·
5,328 Posts
If the battery light on the dash intermittently illuminates, I would say there is likely a problem with the positive side wiring at rear PDC, the harness plug on the alternator, or one of the positive connections in between.

With no battery light and the behavior in the video, I would out bad grounds or ground cables at the top of my list to check if this were happening to me.
 

·
Registered
Joined
·
425 Posts
Sounds like a possible wiring and/or ground issue as others have mentioned but before ya tear into her or focus on that apparent voltage drop - if you have HIDs (premium lighting group) with headlamp flicker a check I'd check the F15 & F16 20A fuses in the front PDC (the one in the engine bay)...those fuses can have issues maintaining good contact over time, they get warm & a bit plastic-y in high temps.

Only takes a min to check too.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #16
But first, any warranty on it?
Sadly, only the powertrain warranty is still in effect

Wiring diagrams and images of how cables and harnesses can be found here:

Bless you for that!

1 of 4 things, I would start with grounds first (this is typically the single most cause of all electrical issues), then alternator, then battery, then ECU (ECU manages voltage regulator for the alternator).


Good luck.

-Kenny
So far grounds seem ok. It's why I also tested between post and chassis and post and engine block. I'll keep swinging away. Thanks


If anything, I would expect a slight voltage drop when testing the 12V supply up front as it is fed from a long cable that runs from the back to the front. Could be a bad intelligent battery sensor (connects to the negative side of the battery) which tells the PCM state of charge.
Because the alternator is connected up front, it makes sense to me. I would expect a very slight voltage drop at the rear, furthest from the alternator, but not the 1+ volts Im seeing.

If the battery light on the dash intermittently illuminates, I would say there is likely a problem with the positive side wiring at rear PDC, the harness plug on the alternator, or one of the positive connections in between.


With no battery light and the behavior in the video, I would out bad grounds or ground cables at the top of my list to check if this were happening to me.
There's no battery light and honestly I am more bothered by the times it hit above 15v than a lower voltage situation. Thanks for the info on the wire routing though, I'll check that out this weekend
 

·
Registered
Joined
·
8 Posts
Discussion Starter #17
Sounds like a possible wiring and/or ground issue as others have mentioned but before ya tear into her or focus on that apparent voltage drop - if you have HIDs (premium lighting group) with headlamp flicker a check I'd check the F15 & F16 20A fuses in the front PDC (the one in the engine bay)...those fuses can have issues maintaining good contact over time, they get warm & a bit plastic-y in high temps.

Only takes a min to check too.
It's just got the halogens, but that's good to know!
 

·
Registered
2019 Charger Scat Pack
Joined
·
18 Posts
As long as you have a VOM, measure the resistance for each cable front to rear, on the positive and negative also.
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,172 Posts
There should not be a 1V drop between the front posts and the battery, unless one of the grounds has exceedingly high resistance.
Or the positive cable that runs back to front has high resistance. There is a junction block on the passenger side (the cable is not one long rung from the battery to jumper post) that could also have contact resistance issues.
 

·
Registered
2015 RT 5.7 M6
Joined
·
6,172 Posts
Because the alternator is connected up front, it makes sense to me. I would expect a very slight voltage drop at the rear, furthest from the alternator, but not the 1+ volts Im seeing.
Yeah, I thought you were testing with car off but I should have known better since the voltages were greater than 12V.
 
1 - 20 of 25 Posts
Top