Intermittent battery light

Tiny
MARK HUDI
  • MEMBER
  • 2003 SATURN ION
  • 2.2L
  • 4 CYL
  • 2WD
  • MANUAL
  • 179,000 MILES
Starting car everything is fine. Battery light goes out like supposed to. Then comes back on, then goes off. Time can vary on length it is on. Had auto parts store check battery. It was 100% charged. Left auto parts store. Car started fine. Then as leaving battery light came on. Remained on for two miles then when I turned AC on light went off and stayed off until home. Then at home started the car again. Everything is fine, disconnected the battery and car kept running fine and no battery light. I am guessing next to look at connections at alternator. Already did the battery.
Monday, July 30th, 2018 AT 3:45 PM

16 Replies

Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello, I am Danny.

Yes, I would check all the connections in the charging system. I have attached a diagram of the charging system. I have also attached a tutorial showing how to test. Hope this helps and let us know what happens. Feel free to ask any questions if needed and thanks for using 2CarPros.

Danny-

https://www.2carpros.com/articles/how-to-check-wiring
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Monday, July 30th, 2018 AT 4:15 PM
Tiny
MARK HUDI
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  • 9 POSTS
Thank you for your prompt answer. I have looked but cannot find anything about a sensor or fuse. Could that be the issue also?
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Monday, July 30th, 2018 AT 4:54 PM
Tiny
DANNY L
  • MECHANIC
  • 5,648 POSTS
Hello again.

Have you checked the Alternator connections? There is no fuse or sensor that would cause this in the charging system.

Danny-

https://www.2carpros.com/articles/how-to-check-wiring
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Monday, July 30th, 2018 AT 6:05 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,087 POSTS
This system senses the battery voltage at the battery feed to the ECM and uses it to tell the alternator when to charge. To test it you would need to measure the battery voltage at the main ECM fuse in the power distribution center, however I would say you either have a bad connection at one end or the other of the power feed cables. Either the battery end or the area it connects to the PDC. It could also be something on the ECM board. For that a scan tool with live data would show you the voltage the ECM is seeing.

Also, never disconnect the battery on a modern car with the engine running, it is an easy way to destroy the alternator and ECM because it will cause the ECM to full field the alternator and that can jump the circuit voltage and current up enough to burn things out.
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Monday, July 30th, 2018 AT 7:26 PM
Tiny
MARK HUDI
  • MEMBER
  • 9 POSTS
Thank you for your reply. Have checked both ends. Appear okay. Now light is intermittent. Yesterday no light. Today light came on half way to work. Came on again on the way home. Then left home to run to store two miles away light went out and has not come back on. And had battery checked again it is at 100 percent.
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Wednesday, August 1st, 2018 AT 3:27 PM
Tiny
STEVE W.
  • MECHANIC
  • 14,087 POSTS
Which cables are you checking? It can be any of the power feeds that are the issue, not just the battery cables themselves, and be sure to check the ground side as well. If all the connections are clean and tight then it is possible you have an issue inside the ECM itself. To see that you need a scan tool that can watch the actual live data.
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Wednesday, August 1st, 2018 AT 7:23 PM
Tiny
MARK HUDI
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Thanks for your help. Just looked at wires connecting to the alternator. And just as suspected no battery light this morning. Can auto parts store do that?
Or does it need to go to a shop?
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Thursday, August 2nd, 2018 AT 7:12 AM
Tiny
STEVE W.
  • MECHANIC
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Parts stores would pull codes only, they do not do live data. The wires on the alternator really do nothing on this car, just turn it on/off and carry the charge back to the battery. The ECM has the voltage sensing inside it and reads the voltage through its battery feed.
On other systems the light is actually connected to the alternator and goes off when the voltage out of the alternator rises higher than battery voltage. In your case the light is turned on/off by the ECM when it sees the alternator changing the system voltage to above battery voltage.

The battery terminal outputs to the fuse box and starter and battery. Also it needs a good ground. So you would check the negative battery cable connections and the engine to body ground connection. Then the alternator battery feed to its connection on the starter and battery as well as the connection to the fuse panel. If those are all clean and tight, then it could be the connection on the ECM itself that is loose or corroded.
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Thursday, August 2nd, 2018 AT 9:26 AM
Tiny
MARK HUDI
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Awesome, thanks for the help. I will reply when done.
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Thursday, August 2nd, 2018 AT 12:44 PM
Tiny
MARK HUDI
  • MEMBER
  • 9 POSTS
Have checked all connections, wires.
Everything seems okay. Battery light still comes on then off. Today went to auto parts store, had battery checked again, a week after this issue battery tested 100%. Am lost now, must be ECM going out?
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Sunday, August 5th, 2018 AT 10:11 AM
Tiny
STEVE W.
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It is possible, but you should really put a scan tool on it and watch the actual charging cycle. That would tell you the voltages that the ECM is seeing as the alternator works. Testing the battery is useless for that. As it testing the charging system as the light is not connected to those, it is a stand alone item.
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Sunday, August 5th, 2018 AT 11:06 AM
Tiny
MARK HUDI
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  • 9 POSTS
Well the part of having battery checked again was to see if the alternator is working. So with a week of battery light on/off seems that it is the ecm going out.
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Sunday, August 5th, 2018 AT 11:53 AM
Tiny
MARK HUDI
  • MEMBER
  • 9 POSTS
New issues today were ran to the store everything fine. Then come home leave ten minutes later battery light comes on. Drive fifteen miles. Park car four hours. Starts right up battery light comes on. Back thirteen miles to a different store. Shut car off. Then will not start. Jump get home and same thing car will not start like battery drained. I do not know what next step to take. Is it the alternator or ECM.
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Monday, August 6th, 2018 AT 1:17 PM
Tiny
STEVE W.
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It could be either, or it could be one of the cables has failed. I have seen more than one that looked just fine be corroded inside the insulation. A way to to test that would be to use a set of jumper cables and connect them in parallel from the battery terminals to the battery cable connections on the car. So battery negative to the engine block, battery positive to the power terminal on the starter. Try to start it. If it now starts up then you have a bad cable.
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Wednesday, August 8th, 2018 AT 9:50 AM
Tiny
MARK HUDI
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Well did the above as mentioned. Same thing car engages but not start. So took starter to auto parts and they tested. Three times test said pass. But as the test was going on smoke came out of the starter three times. Obviously this cannot be correct. Had to go to another AutoZone for part as this did not have one. Even though inventory said yes. Other store tested starter and it smoked immediately. Test over fail. So get new starter in and nothing. Then scrape paint at negative terminal that is bolted to the battery holder. Reattach. And varoom car starts. Run for fifteen minutes no issues. I start again varoom. Ran another fifteen minutes. Start a third time varoom ten seconds later battery light back on. And stays on. I am confused.
Any other help?
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Thursday, August 9th, 2018 AT 8:46 PM
Tiny
STEVE W.
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That sounds like a bad battery cable on the ground side then. They can fail inside the insulation and housing. Then you get an intermittent connection that cannot carry the amperage that the starter needs to turn over, or to charge the battery.
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Friday, August 10th, 2018 AT 4:37 AM

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