[FIXED] 2009 honda civic 1.8 charging system

does anybody have a known good waveform for the altc and alternator fr signal. trying to help a friend out. he says its not charging has power on the big battery wire. voltage dropped that. and power on the blk/yellow wire. voltage dropped the ground. he used a pair of jumper cables hooked to the alternator body hooked to a good ground still not charging. just need to check those 2 signal wires we don't know what we are supposed to see. also the alternator l signal works the battery light comes on with key on engine off

Just posting up a diagram for anyone else trying to follow along:



Just FYI, the Alternator C signal is the only one you need to worry about for no/low charging problem. It's a steady 8V provided by the alternator to the PCM, which grounds that voltage when it wants to shut the alternator off for fuel savings. If you see around 8V on that white/green wire with no charging taking place, then you're good to put an alternator in.

The FR is supposed to be a 0-5V square wave signal which the PCM uses for idle speed control, and nothing else. Zero impact on charging rate. With the alternator unplugged, look for 5V on the white/red wire.

Check this article out if you want, does an amazing job of explaining the operation of these alternators:

opensiuc.lib.siu.edu/cgi/viewcontent.cgi...11&context=auto_pres

backprobing the control wire at idle with loads the voltage is only 6 volts the fr circuit is a square wave 0-5 volts. that looked like the one in the article. wonder if the regulator is bad only sending 6 volts instead of 8

cheryl hartkorn wrote: backprobing the control wire at idle with loads the voltage is only 6 volts the fr circuit is a square wave 0-5 volts. that looked like the one in the article. wonder if the regulator is bad only sending 6 volts instead of 8

Yeah, I hesitated posting that 8V number, 'cause I've seen it be lower before. I think Identifix says 7V? Anyway, I say your friend is good to replace the alternator.

That's a really good article, thanks for sharing.

No problem! That article really helped my confidence when diagnosing these alternators.

so he put a remy alternator on it. drove it for 2 hrs and it died. completely dead. we cut the control wire at the alternator and it reads 5.8 volts. the eld voltage changed with loads and matched what the spec was. at 2000 rpm defrost ac on brights it reads 13.9 volts. wonder if that control voltage 0f 5.8 is to low.

take that back with the ac brights defrost the eld voltage was .9 does that seem low?

cheryl hartkorn wrote: so he put a remy alternator on it. drove it for 2 hrs and it died. completely dead. we cut the control wire at the alternator and it reads 5.8 volts. the eld voltage changed with loads and matched what the spec was. at 2000 rpm defrost ac on brights it reads 13.9 volts. wonder if that control voltage 0f 5.8 is to low.

Soooooo, it's charging sometimes now? :huh:

Nice move cutting the wire, good idea! That 5.8V does sound low, but the cut wire eliminates a resistive short or a bad PCM. I don't think you'd get the alt to charge at 14V with that control circuit grounded...

Not sure about the ELD spec, all the scan data I have just shows ELD amps and not direct sensor voltage. Still, I've never known an ELD to misreport - usually they just fail completely.

Maybe leave the wire cut and see if it stops charging again? I'm wondering if this one will need an OE part to be happy.

he said screw it. took the remy off threw it in the road and got a Honda brand and it all works now. the control wire voltage went up to 7.6 volts and the fr looked a lot better.

cheryl hartkorn wrote: he said screw it. took the remy off threw it in the road and got a Honda brand and it all works now. the control wire voltage went up to 7.6 volts and the fr looked a lot better.

Sweet! What a pain, though... Looks like this is another place where the aftermarket can't seem to get it right.

Slapping a [FIXED] label on this one.

yea we kept wondering about why that voltage was so low. only way itd be low is a bad alternator because it sends it to the ecm even that low with the wire cut?? glad I didn't have to put the alternator on twice. just glad its done

cheryl hartkorn wrote: yea we kept wondering about why that voltage was so low. only way itd be low is a bad alternator because it sends it to the ecm even that low with the wire cut??

Agreed. One of those cases where knowing circuit design was critical. I'll absolutely be looking closer at the Alt C voltage level in the future - I think anything lower than the 7.6V measurement you found indicates a problem.