In article
<cohNOtSPAM-1A3549.13081508122003@news-central.ash.giganews.com>, Charles
Henderson <cohNOtSPAM@i-2000.com> 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

Charlie,
I have a regular voltage testing machine but I was in Kragen's Auto Parts
store yesterday and saw a $9.00 item called "Auto Charging System
Analyzer". I believe they sell the same type of item at almost all auto
parts stores. You can use it to test the battery or test the alternator.
It comes with detailed instructions. I purchased it as a Christmas present
for someone. It may not tell you everything you want to know but at least
it will allow you to test the alternator and battery.