I think you need a simple volt, amp, load test at your corner parts
store. Follow their advise. bob

Charles Henderson wrote:
>
> 1990 Civic DX, 4 Dr., 5 Sp., 1500cc
>
> I've got the Battery light on in the dash pretty much all the time now.
> It was intermittent, not coming on for a half hour or so after startup,
> and either coming on or going out under certain engine load conditions,
> but now it's there all the time.
>
> Honda Service Manual has an Alternator testing procedure that first
> begins by removing the main connector from the Alternator and checking
> for voltage to ground at two different pins inside the connector.
>
> Unfortunately, mine fails the second of those voltage tests, and in that
> case the test procedure refers you to the ECU troubleshooting section at
> that point. Which is a bit of a problem because I don't have the special
> interface cable needed to access the ECU circuits for test purposes, and
> get this: the test procedure for the ECU says "Substitute known-good
> ECU; if problem disappears, replace ECU" at various points in the
> procedure.
>
> Hmmm. I haven't priced it officially yet, but that thing costs in the
> neighborhood of $250 bucks! I can't afford to buy one just for testing
> and troubleshooting!
>
> And if I *had* a known-good ECU, what would I need a testing procedure
> for in the first place? Swapping it out would *BE* the testing procedure!
>
> ;-)
>
> I think the problem is that the ECU has an economy circuit in it that
> shuts down the Alternator under certain load conditions to save fuel.
> Pretty neat idea, except when it malfunctions!
>
> My question: How can I determine for certain whether it is the ECU
> malfunctioning, or if it's some other load/condition sensor giving it
> faulty data? And I suppose it still could be the Alternator itself...
>
> Keep in mind I don't have a "known-good" ECU to follow the official
> diagnostic procedure, and I'm not sure if I can go buy one, use it for
> testing, and return it if it turns out not to be the culprit.
>
> Any ideas?
>
> ;-)
>
> Thanks,
>
> --Charlie Henderson