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Car: 2003 Honda Civic Si G1Wh dash cam, 400w amp, 4300k HIDs

My alternator failed badly (stereo cutting off), no battery light. Replaced it with a reman Duralast, battery light is on. It shows 14.5v while running, and I've had the battery tested at 2 different stores, both good. The car has only died once in 3 months (I leave my dash cam on overnight sometimes). The car has an electrical load detector, but there is no CEL indicating a problem with it. Fuses good, grounds good, alternator connection good. Cruise control doesn't work, and just threw a TPS code, not sure if that's related. What gives?

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  • I'm wondering if it's on due to over-charging. While not an extravagant amount over, most alternators charge at about 13.5-14.1vdc ... 14.5v may just be enough to trip the light. Just a theory on my part, though.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 6, 2016 at 22:08
  • A TPS code might just be 13 year old TPS sensors' batteries dying. Check the code and see exactly what it is.
    – kmarsh
    Jan 6, 2016 at 22:48
  • Check your current draw with a ammeter while the vehicle is sitting when off. You may have a parasitic draw, perhaps through the amp or HID conversion. Also please elaborate on "stereo cutting off". Could this be a short circuit?
    – kmarsh
    Jan 6, 2016 at 22:49
  • @kmarsh does the TPS run on its own battery?
    – Zaid
    Jan 7, 2016 at 3:30
  • Each TPS sensor (usually behind the valve stem in the rim) has a built-in battery. At about 10 years they start to fade. Most often this shows up first in cold weather, you'll actually see the TPS warning on a cold morning and it goes away in the warmer afternoon, because the batteries have warmed up and put out a little more voltage, enough to connect their signal to the sensors.
    – kmarsh
    Jan 7, 2016 at 14:38

1 Answer 1

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Check the voltage of the white/blue wire at the alternator connector. It should be at least 12 volts if the alternator charging voltage is greater than 13 volts. If there is no voltage here then the regulator in the alternator is no good.

This signal goes first to the PCM then to the multiplex control unit and then to the instrument cluster. Testing it after it leaves the alternator is challenging, Honda gives no test procedure for this.

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