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Thread: Battery Light ON but Alternator is Charging?

  1. #1
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    Battery Light ON but Alternator is Charging?

    Title says it all. The battery light is on but the alternator is charging. Output is at 13.5 volts. Alternator is about 2 years old got a reman from Napa it appears to be in good shape. Battery appears good with a voltage of 12.7 when off. No starting problems and no dead battery issues. I checked the air intake temp sensor and the connection is good. The problem appeared at the beginning of summer after I charged the AC system. When I was checking the AC I disconnected the ac clutch wire to see if it was the problem with the AC. Anyway doubt it has any thing to do with it just looking for ideas. Thanks.

  2. #2
    Registered Member wallabe's Avatar

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    Could be a number of problems. First check the fuses (inside and outside the car), then inspect and check the tension on the alternator belt to make sure is tight.

    If that doesn't seem to work unplug the battery for 15 minutes or do the ECU reboot trick and see if it comes back.

    If it does, get a Code reader to pull the code. Come back and post it. Depending on the code it could be something wrong with your IAT sensor or PCM.
    Last edited by wallabe; 08-08-2012 at 04:38 PM.

  3. #3
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    Ok I have some new symptoms...

    First off the battery light is coming on and off. It appears to be heat related. When I am running the AC and its hot out like it has been (100 degree heat) the battery light will come on and the voltage for the car will drop to 11 and then back up to 13.5. I checked the alternator belt tension and it seemed good.

    Now when I am running the car at night with the ac I get no battery light and a voltage of 13.5 right where it should be.

    I also pulled the codes and I am getting:
    P0113 High input on the IAT sensor and
    P1569 VTCS solenoid valve circuit low input

    So I am thinking of a few things. I am wondering if the AC system might be overcharged which could be causing extra heat at the evaporator which is causing the heat issue and putting extra strain on the compressor. Hence the voltage drop at the alternator (belt slipping) and the IAT code for high input(high heat). With the VTCS being unrelated. This all began when I recharged the AC.

    Or alternator is going bad and the IAT and VTCS has also went bad. With the alternator causing the sensor failures due to high voltage which is probably unlikely since there is no code for alternator high voltage.

    So once the car cools I am going to tighten the belt, check the IAT sensor, recheck for codes and the probably reset and then recheck codes again, test the alternator, and also check the charge level in the AC. I guess we will see....
    Last edited by nate2010; 08-09-2012 at 06:56 PM.

  4. #4
    Registered Member wallabe's Avatar

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    More then likely you have a short somewhere in the wires going to the IAT. When I first got mine I had to fix it.

    http://www.mazdas247.com/forum/showt...nsor-unplugged

    You might need to replace it. Autozone here has it for $21. So it's an easy fix. Plus it's right there on the Intake tube. Also you might want to check to see if the tube my need to be replaced also if you still have the stock intake on there. Those things are good for rotten out in the flex part.

    http://www.amazon.com/Dorman-696-601...ir+Intake+Hose

    I'm pretty sure the VTCS code will go away when you replace the sensor. If not just check back here with the update only after you drove the car for a day with the new sensor and the code is still pulling.

  5. #5
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    Ok thanks.
    The intake tube is brand new so it should be alright but I will check it.

  6. #6
    Registered Member wallabe's Avatar

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    How's it coming along?

  7. #7
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    Well I ran the service manual tests on the IAT and the resistance was 1.7 kohm and there was 5 volts on the b side of the harness. The manual said to replace the IAT for the resistance and repair the harness for the voltage issue. I also checked the charge voltage of the alternator and it was at 16volts.

    I had autozone check the battery but it came back good she just had a hard to getting the machine to read it. Also one of the terminals is leaking battery acid...

    I can't afford to replace the IAT alternator and battery so I really need to narrow this down. Kinda at a loss here since I appear to have several issues at once but no specific id on the problem. The only other thing I am wondering about is the ground cable it is in pretty bad shape for the last 5 inches of it and I have cut off the bad cable as far as I can. I will recheck the codes today and see if I am getting a high voltage for the alternator.

  8. #8
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    Just went and rechecked the alternator, battery and codes. The tester says the battery and alternator are ok. I am only getting a code for the IAT P0113 and the IAT is showing a resistance of 1.5kohms to 1.7kohms. So going to start with the IAT....

  9. #9
    Registered Member wallabe's Avatar

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    Keep us posted.

  10. #10
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    Well I replaced the IAT and no luck still getting same symptoms. So I started reading through the service manual and I am pretty sure I found a mistake.

    First off I have code P0113 high input voltage. The reading is at 5.5 volts on the B side of the IAT harness. Now if you are troubleshooting from the service manual for the 113 code when you get to step 4 it says:

    "INSPECT IAT SENSOR
    • Disconnect IAT sensor connector.
    • Measure resistance between IAT sensor
    terminals A and B (part-side).
    • Is resistance within 0.117—28.616 kilohms?
    Yes Replace IAT sensor, then go to Step 10.
    No Go to next step."

    Notice that it says that if the resistance is between the acceptable range it says to replace the IAT. I have determined this has to be incorrect.

    Now if you go back to the service manual and check the code P0112 Step 4 also, which is IAT Low input voltage it says this:

    "CLASSIFY IAT SENSOR MALFUNCTION OR
    HARNESS MALFUNCTION
    • Disconnect IAT sensor connector.
    • Measure resistance between IAT sensor
    terminals A and B (part-side).
    • Is resistance within 0.117—28.616 kilohms?
    Yes Go to next step.
    No Replace IAT sensor, then go to Step 7."

    Troubleshooting 112 at Step 4 it clearly says that if the IAT is within range not to replace it but to continue in the steps.

    This is very annoying to say the least since the money spent on a new IAT could have been used for other things.....

    Anyway I just want to make everyone aware and later today track down the short or open circuit and get my darn car working like its suppose to.

  11. #11
    Registered Member wallabe's Avatar

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    How much did it cost you? I bought mine for $15 from autozone and had to replace the wire which came out to be a total of $22 with the IAT included. I said you may have a shortage in there like I did. When it comes to electrical work in a car it gets pretty darn crazy trying to track down something. But I'm glad to see that you are on top of it.

  12. #12
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    Yeah I could not locate a IAT for that kinda price around here. Unfortunately the cheapest one was 52 dollars... Anyway I can probably just sell it and get some of my money back we will see. I feel robbed for sure.

    Anyway I went through the wires and checked for continuity and everything was good. No shorts or open circuits. Next I checked the pins on the connector and bent them back some to make sure there was a tight connection. Took it for a drive and I am still getting the same symptoms (battery light coming on intermittently). So I grabbed my volt meter and put it on the cigarette lighter and took it for a drive. What is happening is that every time the battery light comes on the voltage is dropping to 12.5 and then steadily declining. Then at random the light goes off and the volts come up to the standard 13.8.

    Also when the alternator is charging correctly the rpms are falling down to 500 or less when it is at idle. As soon as the battery light comes on and the volts drop there is no longer a pull on the motor when at idle. The alternator must be failing at the brushes and the regulator. Tomorrow I am going to pull it off and have it tested and try to hunt down the receipt since it is only 2 years old. There is a slight whine coming from it as well so the bearings are probably going too.

    I do not like buying rebuilt alternators and do not trust them. This has happened before on my wife's Ford Focus. The second replacement of the alternator I went with a Motorcraft rebuilt and it has lasted 8 years now. The one that is on the Mazda was a Napa rebuilt and I usually have good outcomes with Napa but I will never go with anything that isn't brand new or from the OEM manufacturer.

    I guess I will also check the codes one last time to see if the IAT code is still there. The service manual says that it will throw the code for high input voltage when it goes over 4.7v. Last week when I tested it, it was at 5.8 volts. I do not know if it was the crazy 100 degree heat or the damned alternator causing the problem. I did have a reading of 15 volts from the alternator last week so I suppose it could caused the problem. All I know is I've been racking my brain on this one and originally suspected the alternator and should have just went for that to begin with. Oh well this problem will be ironed out soon enough.

  13. #13
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    I got the alternator out and had it bench tested. It still tested good but there is play in the bearings and you can hear the brushes and possibly rotor scraping when you spin it. It was still under warranty so I have a brand new one coming which is only about 25 dollars more. I will put it in tomorrow and hope that the IAT code is gone. However when removing it, it appears that the engine is leaking small amounts of oil from either the oil pan gasket or the front oil seal. I hope to track that down today.

  14. #14
    Registered Member wallabe's Avatar

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    Damn oil, always leaking from places. Lol I hope it works too.

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    It almost sounds like the internal voltage regulator in the alternator is screwing with shit. Guess we'll find out once the new alternator goes in.............

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