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Discussion Starter #1 (Edited)
Have a 2012 (final month of manufacture) GL Sport 2.4l Auto that has a very strage electrical issue. The battery warning light starts to flicker within minutes of driving. The whole dash, lights, CD player, everything will flicker, sometimes all going out for a second, sometimes will settle down during driving and be fine for a few minutes. I have replaced the Alternator, the battery and starter. An electric voltage tester shows voltages to be erratic between 12-18volts. Checked wires, no shorting or bad connections I can find. The car never seems affected in how it drives, just worried about blowing all my lights. Been like this for 7 months, the problem never goes away.

Do I have a bad ECU?

D.J.
 

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Technically, the battery light isn't ONLY related to the battery, it tells you that you have an electrical issue, which the ECU could cause. It could also be the voltage regulator, which tells the alternator to charge or not charge the battery. I'm not entirely sure if there is a voltage regulator on our vehicles, but if it doesn't, I would assume it's the ECU's job to tell the alternator to charge or not.

I'm thinking pcfreak4 would know a decent amount about this, as he's pretty knowledgeable on electrical stuff like this.
 

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Technically, the battery light isn't ONLY related to the battery, it tells you that you have an electrical issue, which the ECU could cause. It could also be the voltage regulator, which tells the alternator to charge or not charge the battery. I'm not entirely sure if there is a voltage regulator on our vehicles, but if it doesn't, I would assume it's the ECU's job to tell the alternator to charge or not.

I'm thinking pcfreak4 would know a decent amount about this, as he's pretty knowledgeable on electrical stuff like this.
Haha thanks for the reference

Yes he’s correct in that the battery light is actually related not to the battery at all really, it’s a malfunction indicator telling you something is wrong with the “charging system” of the car, hence the alternator

Without doing further research through the FSM right now I want to say that the voltage regulator is inside the Alternator

Did you get a new or refurbished Alternator? What brand?

Right now I want to say that you got a bad alternator still or a bad ground, check all the major grounds
 

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The voltage regulator is in fact on the alternator, so it has been replaced. Bad wiring off the alternator, such as a corroded, loose, or cracked shielding could cause this, or even just corrosion on the connection to the battery posts or at the chassis ground the battery connects to
 

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Discussion Starter #5 (Edited)
Thanks all for the info, the fault was there on the previous original factory alternator, I did purchase a refurb, I just didn't think it likely two alternators could have same defect, although stranger things have happened to me. I checked the wiring and grounding and battery terminals, all the obvious things, since the car is like-new condition, I concluded the only thing left was the ECU. But in case the odds are that way, I will replace with a 3rd alternator.
 

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You could check what the ECU voltage is, and compare it to the actual system voltage. If the ECU thinks the voltage is low, it'll request more.

Otherwise, probably not ECU. I can't think of a single example of one of these ECUs failing either without some form of trauma, and even then, they usually survive a crash
 

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Discussion Starter #7
Sounds good, thank you for the advise, I will try that. It's good to know that it probably isn't the ECU.
 

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Discussion Starter #8
If it is the ECU, I have read I will need to aquire a MUTIII device and save the setup to then upload into a replacement. Hopefully that won't be necessary

Thanks!
 

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My car was in a crash in the corner that the ECU sits on and it still works perfectly

I’d say you bought a bum alternator, get a good brand NEW one not remanufactured
 

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Have you considered the dimmer knob on the left side of the dash? It's basically a potentiometer, so it could definitely cause intermittent things like you're describing (although I have to say, I can't imagine it would cause your check engine light to come on). Perhaps that's a separate issue? Have you read the codes to see if it's throwing anything specific?
If you read my post last month (ended up being a bad battery) my car did crazy stuff with lights when the computer wasn't getting enough juice from a failing cell.

Just my 2 cents. Don't know if it's worth checking out, but that little knob would be a very cheap fix if it's indeed bad.

Good luck. Electrical problems are so terrible to deal with.
 

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Usually intermittent flickering would tell me it's a loose or corroded ground somewhere. If you check the voltage at the fuses you should be able to find what circuit is having the issue.
 

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Usually intermittent flickering would tell me it's a loose or corroded ground somewhere. If you check the voltage at the fuses you should be able to find what circuit is having the issue.
I took the 'flickering' as an increase in voltage, which wouldn't be a failure to provide ENOUGH voltage, but a failure to provide information on how much is enough. It does make sense why this happens with a variable 12v-18v system reading.
 

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Discussion Starter #18
Checked the usual fuse box voltages and the system is definitely too high on it's charging. Sometimes the entire dash illumination, radio, everything cut's out for a second, tire warning, engine light, everything flags a proplem for a few miniutes. Stopping, restarting tends to clear for a while. Mostly, when accellerating it triggers the issue, plus the headlights are flicking high low all the time. The alternator regulator does seem the likeliest cause. Waiting for delivery of a new one.

Thanks for all the ideas.
 

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Discussion Starter #19
FIXED!!

It was the Alternator.

So when I replaced the defective alternator with another Alternator and the fault was still there, I spend 6 months trying to find a bad connecition. Turns out I had two defective Alternators with the exact same defect... what are the odds. So the original replacement was a refurb. The second replacement was brand new, resulting in the problems going away.

I wlll never purchase a refurb Alternator again.
 

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FIXED!!

It was the Alternator.

So when I replaced the defective alternator with another Alternator and the fault was still there, I spend 6 months trying to find a bad connecition. Turns out I had two defective Alternators with the exact same defect... what are the odds. So the original replacement was a refurb. The second replacement was brand new, resulting in the problems going away.

I wlll never purchase a refurb Alternator again.
Like I said from the beginning :fever: haha

Well anyway, glad it is fixed now
 
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