Battery light keeps turning on

Tiny
JEEPBOULDER9
  • MEMBER
  • 2011 JEEP PATRIOT
  • 2.4L
  • 4WD
  • AUTOMATIC
  • 140,000 MILES
I keep getting my battery light when I drive. Went to test the battery (brand new) and mechanic said it's all good so as the alternator. I replaced the terminals as well and it has been driving well since until today. I have been having the battery light come up for the past few months now too.
Thursday, August 6th, 2020 AT 10:30 AM

5 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
If the battery and alternator are not the issue then we need to monitor the PCM data with a scan tool to see how much the PCM is turning the alternator on and off. Basically the PCM does what is called duty cycling with the alternator. This means when you need more voltage, the PCM ramps up the output from the alternator and then when it doesn't need as much it brings it down.

More then likely the PCM is the issue at this point. The other possible cause is wiring which is why we need to use a scan tool to find out what the PCM is commanding the alternator to do and go from there.
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Thursday, August 6th, 2020 AT 1:00 PM
Tiny
JEEPBOULDER9
  • MEMBER
  • 3 POSTS
Okay, I will use the scan tool, but I don't own one. Where could I possibly go and check that? Also I would like to add that the car drives perfectly fine and at random times it just comes up and it annoys me. Like just now I turned on my car and there was no light.
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Thursday, August 6th, 2020 AT 1:09 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I am not aware of any places you can take it to use a scan tool but dealers and shops all have them. Clearly they are going to check it for you and not let you use their tool. The other option is to purchase one. However, I would not recommend this unless you are planning on using it moving it forward. It is cheaper to allow others to do it unless you are going to diagnose your vehicle moving forward. However, if you do buy a scan tool you need one that can monitor live data and specifically alternator duty cycle in this case, so I would call them before you buy it and ask if they can tell you what they are able to monitor before you buy it.
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+1
Thursday, August 6th, 2020 AT 6:34 PM
Tiny
JEEPBOULDER9
  • MEMBER
  • 3 POSTS
Update: My car broke down in the middle of a road and had some assistance by a good person. Popped my hood up and the terminals were kinda lose so we tightened them very tight and it ended up doing the trick.
Thank you for all the help!
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Monday, August 10th, 2020 AT 6:57 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
You are welcome. This is a lesson for me to not jump over the basics. After checking the battery state of charge, checking connections is the next thing to check. Sorry I did not mention this earlier.

Thanks for the update and that info will surely help someone else that visits this site. Thanks for using 2CarPros.
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Monday, August 10th, 2020 AT 7:15 PM

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