My "battery light" (charging indicator) has been coming on recently when idling. At higher rpm, it goes off...unless I am running the AC compressor, then no amount of rpm will make it go off. Headlights will make it come on also.

I checked voltages. ~12.65 battery voltage and ~14.5V with alternator running. Seems normal there.

I decided to check the brushes after reading some posts of similar problems on this forum. One of the two brushes was definitely at its service limit. So I replaced with a new brush assembly. After replacing brushes, I still have the battery light at idle or AC compressor come on.

So now I am charging the battery (battery is 3 to 4 years old, I think) with a charger (basic manual charger, 6 amp setting). It has been on the charger for about 5 hours, charge amps down to 3A. So I decide to try it all again. Still...battery light on at idle...yada,yada. Will charge more overnight and try again, but I don't expect anything different.

So what next...voltage regulator? New battery? Whole new alternator? Surely its not the ECU?
I was trying to avoid the whole new (rebuilt) alternator due to extra labor involved and the poor quality of rebuilts I've been reading about.

What other voltage checks can I do around the alternator? I checked the AC voltage across the battery while the car was running (supposed to determine if diodes are good or not) It was less than 200 mV. Thats OK I suppose.

Voltage regulators cost about the same as a rebuilt alternator from Autozone or O'Reilly. Why would one not buy the whole alternator and scab the regulator off of it and keep the rest for other spare parts?

Thanks for all input,

Todd K.

 

If alternator light is coming on, the battery is discharging at idle. This means voltage is < ~12V. Did you check voltage at idle? Most likely explanation is a faulty rectifier, which is limiting amperage output.

One other possibility is a slipping harmonic balancer/crankshaft pulley. Mark pulley w/ a radial line (heavy black felt marker) and watch for any gap developing in the line indicating the rubber bushing is slipping.

good luck

 

Idle voltage is ~14.5

 

I would recommend downloading an Accord Shop Manual. There is a 91 Accord manual at hondahookup.com that can be downloaded.

See diagnostics for Alt light ON and system charging. Sounds like a Integrated Control Unit fault.

good luck

 

Is an ICU failure common? I also am starting to believe this is where the problem is. Or how about the Electric Load Detector? Seems like that could cause a false battery light also.

I took the car to O'Reilly today to have them test the charging system. They basically use a voltmeter with a load bank across the battery. I suppose if the alternator voltage doesn't drop with the load, then the alternator is OK. Anyways, after putting a 46 A load on the battery (car idling), the tester said battery and alternator where "Good"

Thanks,

Todd K.

 

It sounds like a short failur at the wireing harness at the back or between the battery and the alternator..after that I can't tell you much more...

WheelBrokerAng

 

Update:

I checked the voltages again just now. Things seem to be getting worse.

At idle 14.3 V. OK. Under "full load" (AC compressor and headlights) at idle 11.8 V !!!!. Revving engine, it only climbed to just over 13 V. Now this is much more telling than the first time I checked and I was getting 13.4 V at full load, at idle.

Todd K.

 

Strange that OReilys tester didn't pick that up. Maybe intermittent? Maybe happens when you pull the wiring harness one way or the other?

 

Final Update:

I went ahead and put in a reman Bosch alternator this weekend. Problem fixed. I think it was the voltage regulator , which is on board the alternator.

Thanks for being my sounding board.

Todd K.