Battery light on, need help.

TySpeed3

TySpeed3

Greenie N00B Member
Greenie Member
Alright, 2007 Mazdaspeed 3. Have battery light on. Tested it myself, 12.8 v before car was on and around 11v when car was running without load. Took it to oreilly and tested while car was running, and said battery is good (but voltage was low (10.4v w/load)) and also said alternator was not working. Took alternator off car, tested at 2 places, 2nd place put out 15v. Checked grounds (motor mount, negative post, and the 2 on transmission). Put the alternator back in today, 12.8v before turning car on, 14.08 v while car was running under load. Left car running for about 5 minutes, then battery light turned back on and checked voltage and it was 11.08 or so volts. Drove for about 12 minutes each way to get dinner(battery light on entire time) and on way back about 1 minute from my house abs and traction control lights turned on as well as the battery light. What else should I be checking? Charged battery a week or so ago and first time battery light turned on completely was a week ago. It flickered a few times previously, but not consistently until last weekend. Any more ideas? Could it be ecu? Thank you
 
Check all of the connections again and pay careful attention to where the wire meets the connector itself. It seems like an alternator problem but since that checked out it must be somewhere in the wiring.

Have you confirmed that the battery is good?
 
Easter Bunny said:
Check all of the connections again and pay careful attention to where the wire meets the connector itself. It seems like an alternator problem but since that checked out it must be somewhere in the wiring.

Have you confirmed that the battery is good?
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Got battery tested yesterday and everything tested find with that too. I think I'm going to have to trace wires in the engine harness and see if I can figure anything out...
 
Did they just do a quick test at the counter or did you drop it off for a full bench test? I had a battery issue a few months ago; it wouldn't hold a charge and tested fine with their quick initial test, but I asked them to bench test it to be sure and wouldn't you know....she was kaput. No issues since the replacement.

I also previously had an issue a couple years ago where the positive cable from the alternator to the battery burned up due to corrosion, and would no longer charge the battery. I chopped that bit out and spliced in a new line, and it's been g2g.
 
SharksInSpace said:
Did they just do a quick test at the counter or did you drop it off for a full bench test? I had a battery issue a few months ago; it wouldn't hold a charge and tested fine with their quick initial test, but I asked them to bench test it to be sure and wouldn't you know....she was kaput. No issues since the replacement.

I also previously had an issue a couple years ago where the positive cable from the alternator to the battery burned up due to corrosion, and would no longer charge the battery. I chopped that bit out and spliced in a new line, and it's been g2g.
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For the battery, it was a quick test, but I can go drop it off for a bench test if needed. The alternator was tested on and off car. Failed on car (wasn't charging battery) , passed off car twice. I will have to check all the wiring, as that is my next step at the moment. Thank you.
 
A test with another battery, would help eliminate if your current one is weak, or a bad cell. Automotive batteries can have a cell open and some smart ecu's see this as a fault and can stop charging. Wiring is a pain on alternator for access. Especially if you have jumper cables and a good battery to try.
 
Is the problem persistent when the alternator is hot? The alternator would have cooled off by the time you got it to a bench test facility. Heat could be affecting the voltage regulator. Just a thought.

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SyntheticAtmosphere said:
Is the problem persistent when the alternator is hot? The alternator would have cooled off by the time you got it to a bench test facility. Heat could be affecting the voltage regulator. Just a thought.

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So the regulator is built into the alternator, but its regulated from ecu? And yeah, it seems that the problem is when the motor is hot.
 
Cfoldone said:
A test with another battery, would help eliminate if your current one is weak, or a bad cell. Automotive batteries can have a cell open and some smart ecu's see this as a fault and can stop charging. Wiring is a pain on alternator for access. Especially if you have jumper cables and a good battery to try.
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Just another battery? Or one meant for the speed? And how would I use another battery to test (I'm not very electrically inclined)
 
Just change the battery for a known good one. Doesn't have to actually be for the speed as long as it fits and has enough amps to start the car
 
If the issue is when the motor is hot then most likely the contacts inside the alternator are bad. This would explain why you had good test results on a bench test. The alternator was probably cold and not 200 degrees so the contacts inside were working as they should.

Make sure the connector is fully seated for the alternator. Also check the battery cable at the alternator and do a voltage drop test across the cable. Anything over 200 mV would indicate a bad cable. Just put one lead on the alternator post and the other lead at the battery post. Disable your injectors by disconnecting the big connector near the intake manifold and have someone crank the car while you monitor the multimeter. If the meter has a MIN/MAX setting use that.

Most likely your alternator is just bad
 
How old is the battery?

Lead acid Batteries can mask their real condition and pass many "sophisticated" testers.

That being said, when your car is running, the intended design is for the alternator to be the power source. If you measure less than ~13.5V when the car is running then you your system is struggling to or not charging. A battery can short internally and cause a really low voltage reading, but if that were the case, you wouldn't be able to start your car... unless you have been getting really lucky.

It wouldn't hurt to replace an older battery, but from what I am reading, that is not the likely root cause.

If you can recreate this condition very easily, check the resistance in the heavy gauge wire between your alternator and your battery +.

Also, check for DTCs (codes), just because you don't have an engine lights, doesn't mean there are no codes.
 
Easter Bunny said:
Just change the battery for a known good one. Doesn't have to actually be for the speed as long as it fits and has enough amps to start the car
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Checked grounds. Alternator body to motor mount ground, alternator body to negative terminal, negative terminal to body. Checked from positive alternator to positive battery, all good. Checked from positive alternator to body alternator, high resistance, so good. Checked truck battery, 12.2v off and cold, 14.8 when running in truck with headlights on. 12.23v in mazda with car off. 13.9v W or w/o load. The car did not completely warm up yet.

The_big_dill said:
How old is the battery?

Lead acid Batteries can mask their real condition and pass many "sophisticated" testers.

That being said, when your car is running, the intended design is for the alternator to be the power source. If you measure less than ~13.5V when the car is running then you your system is struggling to or not charging. A battery can short internally and cause a really low voltage reading, but if that were the case, you wouldn't be able to start your car... unless you have been getting really lucky.

It wouldn't hurt to replace an older battery, but from what I am reading, that is not the likely root cause.

If you can recreate this condition very easily, check the resistance in the heavy gauge wire between your alternator and your battery +.

Also, check for DTCs (codes), just because you don't have an engine lights, doesn't mean there are no codes.
Click to expand...


Battery is about 3 years old and in Phoenix AZ, so hot most of the year. 12.5v with car off 13.9v with ac and lights on at alternator and at battery. ( Car is not completely warmed up yet. Checked for codes, nothing. Will update shortly
 
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Are those voltages with the truck battery in the speed?
 
Easter Bunny said:
Are those voltages with the truck battery in the speed?
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Yes, they were, once the vehicle was up to operating temp, the alternator stopped working. Tried to reset the computer by unplugging battery, and as long as the engine was warm, the alternator did not work. We checked voltage at alternator and at battery when the moto was cold, it was at 13.9v for both places. Checked without car on and no voltage drop from battery to alternator either. Took truck battery off (after motor was warm) and put speed battery back, and alternator not working. So this proves that the batter is fine.
 
To be honest, I still don't know what's wrong. Alternator works for a bit when battery is charged, but turns off after a few minutes. I'm not sure what to do at this point, running out of hope.
 
I'm guessing the regulator is failing. I'd replace the alternator. Electrical components dont like heat, especially when they get old. Either that or the heat is causing physical movement (ie: expansion) and breaking contact. Seeing as the unit is integrated, the alternator gets replaced as a unit. If this is the original alternator it has served well.

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SyntheticAtmosphere said:
I'm guessing the regulator is failing. I'd replace the alternator. Electrical components dont like heat, especially when they get old. Either that or the heat is causing physical movement (ie: expansion) and breaking contact. Seeing as the unit is integrated, the alternator gets replaced as a unit. If this is the original alternator it has served well.

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Yup good very much be heat expansion messing with the magnets /glue, even even pulley bearing so even though it passes the bench check once it's at temp it doesn't work.
 
As a side note, from my personal experience a failing alternator will usually result in a shorter battery life as well. Be prepared to possibly need a new battery in the future as batteries do not like to be mistreated. Batteries like consistency.

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