Last night I started to hear a chirping sound from the alternator. On my way home I got the "service charging system" and voltage fell to 11.5V. I had to drive ~5 miles home and by the time I got there it was down to 11.1. Luckily I made it home but now I have to drop a couple bills on an alternator. Not sure if the strain from the supercharger tensioners have anything to do with it.

After some quick CF research it appears the connection from the alternator to the battery routes through the starter solenoid and if it gets loose it will melt the terminals so I'll check that first. If thats it the starter is another couple bills unless I can find a solenoid somewhere.

 

I get the same message on the DIC from time to time. My car has underdrive pulley and the radiator fans seem to come on sooner and with more speed (drawing more current?). It's always while I'm idling and the radiator fans kick on when I get the message. I can get the rpms up and the voltage increases. I've been considering a high output alternator or reprogramming the fans to resolve the problem. Please post your findings.

 

The more I read the more I think it is a problem with the.....ready?.......wait for it........


HORN

"...The ECM monitors the generator field duty cycle signal circuit. The system voltage sense circuit receives B+ voltage that is Hot At All Times through the HORN/ALT SENSE fuse in the underhood junction block."

My horn has sounded funny since installing my blower. Recently I installed a new horn from Autozone which didn't cure the problem. It still sounded funny. Then recently I noticed it wasn't making any sound at all. It's likely the fuse is blown which prevents the system from charging...

If this is it I'll be happy I saved ~$225 on an alternator but dismayed at the engineering genius who tied these two things together with the same fuse.

 

From spins thread, try changing the plugs out too.

 

Well I checked the horn fuse last night and it was not blown. Horn still does not work but I think as long as the fuse is intact that rules that out. So plugs are next. It's definitely not the alternator because I put a multimeter to it; from the alternator log to ground and it is spitting out >14V. But the battery shows 12.5V with no ignition and 11.5V with the ignition on. So something is keeping the alternator voltage from getting back to the battery. I crawled under and looked at the lugs on the starter solenoid and they did not look loose, burnt or melted. I'll drop it if the plugs don't do the trick.

 

Good info!

 

My second alternator was an off/on/off thing for a couple days, then went about 2 weeks with no problems before it really died. It appeared to revive itself just before the time when I could check it, which made it seem like the alternator was not the problem.

Just for reference, things don't go wacky until you're under 11v and the engine will quit as you go below 9v.

 

More than likely you have a bad ground somewhere. My guess is at the starter. Check to see if the nuts worked loose.

 

It's gotta be that because a multimeter off of the lug of the alternator shows 14.5 but the battery is not seeing it. Still I'm going to change the plugs before I dtop the starter. Its needs plugs anyway. If after the plugs and starter it still doesn't want to charge I'll be stumped.

 

Just got done putting in a fresh set of TR6's and it charges correctly now.

I never would have thought to do that if Spin hadn't mentioned it and even when he did I thought he was but seeing is believing.

I love you SpinMonster. You're my hero!

 

unbelievable!

 

Is the alternator still chirping? That is odd..

ps one of my horns went out too, the low one. My mean looking car sure sounds whimpy when I hit the horn!

 

The chirping actually wasn't coming from the alternator. It's coming from one of the blower tensioner pulleys. I think I jumped to conclusions when the charging system went whacky.

 

I forgot to post up that the problem came back after two days.

So I tried all the tricks in the book for this. Changed plugs because NGK's are said to create noise that prevents the charging system from working, disabled the P0621 code because that has worked for others who get the DIC message but have good voltage, re-installed my OEM horns because the aftermarket one I had stopped working and the alternator shares the horn circuit, and checked the starter because the alternator and battery junction there. It ended up being the starter connection. The top most stud on the solenoid is where the battery and alternator wires meet; They are screwed onto the same stud. When I looked at it the first time all looked good. I took another look last night and actually felt the studs and the top one was loose. The nut was barely on more than hand tight. Even after taking the nut and wires off the stud was very loose inside the solenoid and there is no way to screw it in to tighten it but when I put the wires on and tightened the nut it all got tight. After that the charging system went back to working normally. I'm thinking it may come back if tha stud breaks loose from inside the solenoid but we'll see.

 

Thanks for keeping us posted Bill. I got the message after the underdrive pulley was put on but I turned off p0621 years ago and all's been fine so far.

My lower horn quit too....that's odd that yours did too.

 

Hey Joe, I get the message after having an underdrive pulley installed also. When my car was tuned they changed the fan settings. I get the message when the car is idling and the fans come on, is this the same thing happening to you?

 

Actually, no, as I recall mine would always happen while cruising along at about 40 mph which I found very odd.

I suspect, but don't know, that somehow the computer expects a certain wattage at certain rpms and with the under drive pulley the alternator puts out less than the algorithm calls for..... so it throws the super loud "ding ding ding" (and man is it annoying) and puts "service charging system" on the DIC.

 

Very helpful thread 5 Liter Eater!

Joe,

I checked your sig but didn't see it, which underdrive pulley are you running?

Thanks,
John

 

Hey John,

I think it's the SLP underdrive that just about everyone uses. It was an off the shelf item.

On a separate note, to my hometown buddy, sorry to hear Gateway closing, but check this out - they are trying to re-open a new Mid-America Raceway! I still have 2 MAR trophies and a couple of treasured "where history drags on" MAR t-shirts. I hope it comes to pass!

http://www.marpark.net/

 

Almost the same issue I'm having. Same issue at the alternator post, except when I checked it, the boot just crumbled away. Meaning that the alternator has been cooking it for some time. But I did have the same issue with the nut being loose and the connection being bad.

After tightening it (repeatedly) over the last couple weeks, having the voltage jump back to normal, only to start dying again once the car heats up, the bearing has started to audibly fail. For me, the main problem is my voltage regulator is burnt up.

The alternator GM puts on the C6 is juuuuuuust enough to get by the extra 15% requirement of a stock car. Our supercharged monsters tax the alternator far more than it was intended with more active fans and pump boosters

Though having been gone a number of weeks, I'd missed the posting about the plugs and the friggin' horn circuit. Jeez.

Unfortunately for me, mine is past any easy fix. Now I'm just looking for 180-200 Amp options...