LS - 1st and 2nd Gen (1990-2000) Discussion topics related to the 1990 - 2000 Lexus LS400

Battery discharge light

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Old 08-07-16, 08:34 AM
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Dex334
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Default Battery discharge light

Alternator not charging but discharge light never comes on. Discharge light doesn't come on with ignition on and engine off either. All other indications are normal. Battery slowly discharges.
Old 08-07-16, 10:08 AM
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oldskewel
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I would first measure voltage at the battery with the engine running. That will be a more direct test of whether you've got a charging problem.

The problem could be a burned out bulb, but not likely, especially since you mention that you really do have charging problems.

From experience with a different car, I know that some alternator failures can cause this problem = the charging light goes out and never ever comes back on (i.e., even with ignition on and engine stopped), until the alternator is replaced.

So my bet is on a bad alternator, but it is a weird failure, so keep an open mind and take measurements, etc.
Old 08-07-16, 10:22 AM
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Dex334
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Tested will engine running and the voltage slowly drops. Goes to 11.6 soon as car is started and slowly goes down. Battery at 12.7 in off position. This shows the charging problem. The discharge light never coming on with ign on and engine off is what seems weird.
Old 08-07-16, 01:13 PM
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Check these fuses.

Old 08-13-16, 12:47 PM
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Dex334
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Thanks to all that replied . Replaced alternator and all problems gone. The discharge light is run by the regulator . Bad set-up. If regulator goes out you get no warning light . Battery slowly dies and you are stuck with no warning.
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Old 08-16-16, 11:57 AM
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oldskewel
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Originally Posted by Dex334
Thanks to all that replied . Replaced alternator and all problems gone. The discharge light is run by the regulator . Bad set-up. If regulator goes out you get no warning light . Battery slowly dies and you are stuck with no warning.
.
Glad you got it fixed. I'm not surprised at the result.

But what you can do (and what I learned to do following my similar experience) is to make it a habit of checking the instrument panel lights after turning the key to on, and before starting the car. When the charging light does not come on before starting, that there is your warning light that something is wrong. Similar, but different ... the oil pressure light should also be on at this time; if not there is a problem with the oil pressure measurement, circuit, or light - but the oil pressure itself (when engine runs) could be just fine.

Taking that even a step further is to notice the instrument panel lights immediately after turning the key on but before things settle out. That is where you can look for a burned out bulb, since everything should light up for a moment at least.
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