Battery light on after replacing alternator and battery

Tiny
WOLFPACKFAN84
  • MEMBER
  • 2010 LINCOLN MKX
  • 3.6L
  • V6
  • 2WD
  • AUTOMATIC
  • 140,000 MILES
Battery light came on and the battery tested bad so I had it replaced. I was good for a few days and then the battery light came on again so I had the alternator tested and it was bad, had that replaced (remanufactured). While the alternator was being replaced they noticed the ground wire was corroded and the power wire from the alternator to the battery was too hot to even touch. Both wires were replaced. The alternator fuse was checked and it's good. Battery light is still on. When returning the core, I had the new alternator and battery tested and both were good. Voltage output over 14. What do I check from here? I've seen where it could be related to the PCM. Is there any way to test that? Are there any codes that should have been cleared after the repair?
Wednesday, February 10th, 2021 AT 1:13 PM

3 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Yes. This could be a PCM issue but normally that is due to the voltage regulator is internal to the PCM. However your voltage regulator is on the generator. So that means it is being told what to do by the PCM but the regulator in the generator.

Here are some guides that help with the proper testing that we need to do for the battery and generator:

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/car-battery-load-test

If this is what was done and they both passed but we had hot wiring then I suspect we have more wiring issues to the PCM from the voltage regulator or the PCM itself if the issue.

Take a look at the info below that will help with this. Specifically we need to find out if there are codes. If we have some codes then we can figure out why the light is on.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Let me know what questions you have. Thanks
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Thursday, February 11th, 2021 AT 4:48 PM
Tiny
WOLFPACKFAN84
  • MEMBER
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Will there be any codes if my check engine light isn't on? The only light I have is the battery light. Also, I have drove my car to work the past couple days (about 10 miles one direction) just to see if I notice anything off. The only thing I've noticed is that when I crank in the morning it is idling at 1,500 RPMs. After a minute it comes down to about 500 RPMs and that's when the battery light comes on. Not sure if that means anything or not but it was not idling that high at start up prior to the alternator and wires being replaced.
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Friday, February 12th, 2021 AT 6:20 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Yes. There can still be codes even though the check engine light is not on. Most codes will trigger the check engine light but there are others such as voltage issue codes like this that would not turn it on.

As for the RPMs being high could be normal but I think that supports this as the PCM will raise the RPM when it sees the voltage is too low.

So I suspect we have a PCM issue but let's start with codes and go from there. Thanks
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Saturday, February 13th, 2021 AT 4:21 PM

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