2010 Dodge Journey Charging Fault. Battery Dies Under Load.

Hello everyone,
The car came in with low voltage complaints. I made a quick diagnosis of it being the alternator based on the running voltage ( this was a bad move) I replaced the alternator just to find the car was not fixed!
I got both alternators (Old and new) bench tested and both are supposedly Good!
I tested the field control wire for a short to power, an open, or a short to ground. Tested Good.
I connected the lab scope to the field control wire while running and Got battery voltage (The description says I should have a PWM 12v Square wave)
I was not able to control the duty cycle of the alternator with either of my scan tools (returned conditions not met error)
I Commanded to duty cycle to 50% (max this test allows) with the key on and engine off.
Below are the waveforms I got at 0% and 50%.
Wondering what you guys think about this issue. It's like the square wave is overlayed with something else.

Thank you!
Elijah

I think I accidentally opened this thread twice....

That's definitely a strange looking waveform. :huh:

To be clear, you're taking this capture at the brown/grey wire while backprobed at the alternator, correct?

If I were you, I'd switch it up and try a substitute load instead. An incandescent test light would work. A 921 or 1157 bulb would be better. One wire of the bulb to the brown/grey wire, the other to ground. Use the alternator field control bidirectional test just like before and see if the bulb lights. Or just start the engine and watch the field control %. If it lights, the field control circuit is fine.

Have you checked voltage drops across the alternator B+ and case while it's not charging? Does the battery test well?

The capture was taken with the alternator unplugged at the brown gray wire.
With a incandescent test light on that wire (alternator unplugged per factory test specs) I get a dim light with low duty cycle and a brighter light with the higher duty cycle.
I did not do a voltage drop while it was not charging.
I also put an amp clamp on the alternator + and was only seeing 60 amps.
With the engine running, the waveform on the brown/gray field control wire goes to a flatline near battery voltage.
Even though the test light lights, is it not a problem/fault to see that funky waveform?
The battery is not new….. I don’t have a great way to test it other then a carbon pile tester…. It tests weak, but not bad.
Would a weak battery cause the whole charging system to not work and eventually stall the vehicle?

Eli wrote:

The capture was taken with the alternator unplugged at the brown gray wire.

Gotcha. Thank you for the clarification.

With a incandescent test light on that wire (alternator unplugged per factory test specs) I get a dim light with low duty cycle and a brighter light with the higher duty cycle.

Perfect. I'm happy with the field control circuit.

With the engine running, the waveform on the brown/gray field control wire goes to a flatline near battery voltage.
Even though the test light lights, is it not a problem/fault to see that funky waveform?

I can't say I've ever scoped the brown/grey wire while unplugged, so I don't know what that's supposed to look like. The odd pattern might be the result of being unplugged. The test light result is enough for me.

I did not do a voltage drop while it was not charging.

That'd be my next suggestion. It'll suck because of where the battery lives on these. :silly: But still worth doing.

I also put an amp clamp on the alternator + and was only seeing 60 amps.

Really? :huh: That's not terrible output. Not full field, but obviously the system is capable of output.

The battery is not new….. I don’t have a great way to test it other then a carbon pile tester…. It tests weak, but not bad.
Would a weak battery cause the whole charging system to not work and eventually stall the vehicle?

Would a weak battery cause the charging system to not work at all? Probably not. Cause it to struggle? Definitely.

The 60 amps output you saw might be a good indication of that. What was the battery voltage when you saw the 60A output?

I will do the voltage drop test.
The battery voltage was around 11v with all loads applied ac/blowers/defrost/lights
Runs 13-14v with no extra loads.

How is pin fitment at the connector on the alternator? Have you checked voltage out of the alternator right at the b+ stud?? What does voltage sense read on the scanner vs target voltage??

Go from alternator case to block ground and look for voltage drop. Block ground to battery negative post

m.youtube.com/shorts/8iivZfSRTus