NavyC4S

I suggest replacing the battery (optima yellow-top) then having your tuner physically turn the code itself off, not just reset it but turn off the code itself.

Fran did mine. Thank you Fran!

carlrx7

90 % of the time.. the battery gets drained. then the alt trys to charge it, which kills that too. so change battery and alt at the same time..

If you ever drain your battery,, dont jump the car, fully recharge the battery.

the alternator is not designed to recharge the battery, only to maintain the charge.

-carl

HOXXOH

I went into full electrical failure mode a few days ago. Put in a fully charged temporary replacement battery which got me 24 miles before the engine quit. Still had 6 miles to get home. Weird DIC messages included "ice possible" (it was 95 degrees) and "maximum speed 158 MPH". Pulled the battery and took it home to charge, then returned later and got the car home.

The voltage started each time around 13.5 and continued to drop, except for a couple of times it bounced back to normal for a mile or two before dropping again.

In searching for replacement alternators, I came accross this.
http://cgi.ebay.com/ebaymotors/Corve...Q5fAccessories

I'm understanding that the pulley has a clutch internally that disengages at high RPM to avoid alternator damage. I suspect that the clutch has broken and won't engage anymore except sporadically. I'm pulling the alternator tomorrow and will report back here after the local rebuilder does the repair.

It makes me wonder if these occasional "Service Charging System" messages are the result of a clutch pulley failing to re-engage.

The Clevite Kid

I am having intermittant "Service Charging System" messages now myself.

All was FINE from early April 2009 (when engine work including UD pulley was done) including driving from Miami to Bowling Green for the C5-C6 bash, until July 31 when the NGK cold plugs went in and Jeremy Preston did a dozen dyno pulls to redline for final tuning. As we drove away from the dyno we got the first "Service Charging System" on the DIC. By the way I have had MSD plug wires installed for over a year.

The message is brief, can occur at any voltage between 12.8 and 13.9, and is a pain in the ear. Jeremy suggested going back to ACDelco plugs, so I will change them this weekend.

I put an Optima Redtop in 2 weeks ago to replace the 3-year-old OEM battery, and still get the message occasionally. If the plugs don't cure it, I will try changing back to the OEM plug wires.

The idle is set at 825, and the system voltage is screwy. At idle it will sometimes read 13.8 or 13.9, and at other times drift down to 12.8, then come back up. The voltage regulator and/or the alternator itself is either getting bad commands from the computer, or they are heading south.

So . . . . . . . I, too, am interested in a real understanding of this phenomenon.

HPSFLORIDA

We have seen this problem twice now, and after a little digging we found that GM has a bulletin regarding the 0621 code and spark plugs. It simply states that if any spark plug other than AC Delco iridium plugs are installed this code may appear. The fix was to remove the NGK Tr55 or TR6's and replace with AC Delco factory plugs.

We did this, left the code active in the tune and the customer has had no issues since. The Pulse technology of the NGK plug or other aftermarket plugs must have an interference with the electric systems and cause the service light to come on.

Hope this helps, because we spent many hours trying to resolve this and it came down to a 20 minute plug change.

Jeremy Preston

Joe_G

I can trace my Service Charging System notifications directly to my underdrive pulley installation. I raced before and after that, did everything the same. Never got the message until I installed the underdrive pulley.

I had symptoms exactly like Lee above...and I never changed plugs.

I SUSPECT (based on readings in this forum on how the alternator charging circuit is now computer based, not just old school mechanical (really old school) or electronic controlled), that the underdrive pulley causes the alternator to output a different voltage than the computer is expecting for a given RPM....as obviously the alternator is going slower than the computer thinks it is for a given RPM, and given the slower alternator, voltage output from the alternator is less than expected and a fault code is set. Thus the service charging system message AND ANNOYING LOUD DING!.

That is pure speculation on my part.

I deleted this code (p0621 from memory) what a couple of years ago....and have had ZERO problems in my daily driver. YRMV.

Jeremy we were typing at the same time! I'd say your experience is a lot more vast than mine so folks should listen to you here. But I'll leave my post up, as it's true I just deleted the code years ago and all's been fine.

turbo2001

I've experienced the same but was told because of the 300 to 400 Idle surge i have from and aggresive cam that this could happen from time to time it surges from 700 to 1100 rpm's depending on her mood just some food for thought's.. I'd ignore till you have an issue.

KMK454

I solved mine, but you won't like the answer...

Never had a service charging system (SVCS) message until after I did a cam and pulley. The UD pulley is negated by the idle of 900 RPM... or not. So I took the pulley off. SVCS still happened, but not as often. Changed the alternator to a new one, and SVCS happened less often, but it still happened. The Optima Red Top also failed a few times, so I put the AC Delco factory unit in. SVCS still happened, but now even less. I'm now back to the stock cam, at which point I had the car re-tuned. I have not had a single SVCS message yet. So take that for what it's worth...

Ted P

I've had the service charging system light go from time to time all summer this year when at idle even though it shows 12.8 to 14.3 volts. No cam no pulley just headers 3 years ago. Read somewhere if you hit the rev limiter you may see this issue.

Wingrider

Like others, I intermittently get this message, and have the original plugs in the engine. The Dealer, Bill Kay Chevrolet, a very experience Vette dealer, took a long look and said first, the battery was fine, second, the alternator was fine, third, there is no drop in voltage when the message appears. Last, all they can figure is that this is a computer glitch, and they really have no solution. I am thinking of shutting the code off.

KMK454

My friend had an old Aerostar van. The check engine light came on, so his fix was to put masking tape over it. The motor went unchecked and running smooth for at least another 50k miles.

Anyhow, if your voltage is normal yet you still get the message, then who knows...

The Clevite Kid

Tuesday night I decided to pull the intake manifold off to check for a possible air leak, put a little sealer on it, and reinstalled it last night. So tonite I take the C6 out for a spin, and after a couple of miles heading down Old Cutler, I notice that the voltage needle is LOCKED on 14.1 volts!

No fluctuation like I have seen before. At the stoplight at SW 88th St. at idle with headlights and A/C on, it drifts down to about 13.8 volts, then pops right back to 14.1 volts as I take off. So I hit the DIC to display battery volts, and while cruising, 1500 rpm on up, the voltage is STEADY at 14.1. After a while I cut over to U.S. 1 to get a lot of stop-and-go action, and at every stop, idling at 775 rpm, WITH a 25% underdrive pulley, the voltage drifts down to 13.9, or if it is a loooooooong light, 13.8, and then as I resume driving, the volts pop right back up to 14.1.

Total of 30 miles of stop-and-go tonite - I would have gotten about a dozen "Service Charging System" messages a week ago - and not one DING-DING-DING, no messages, and rock steady voltage. SO what is different?

Three things:
1. I had the battery disconnected for a while during the manifold work, and that may have "reset" something (yeah, right ).

2. The hot cable to the alternator had been laying right against the left front spark plug wire, and I re-routed it to keep them about an inch apart.

3. I retightened the connection of the alternator hot cable nice and snug with the 3/8" drive ratchet and a 13mm socket.

Number 2 would have reduced the induction of ignition noise into the alternator, where signals are sent to the ECM to control voltage. Number 3 could have corrected a high-variable-ohmic connection between the alternator and the battery.

Anyway, I think MY PARTICULAR "Service Charging System" odyssey is over. Like cancer, I think there are multiple causes of this phenomenon. But you might as well try this cheapest-of-all approaches before moving on to replacing things.

And the set of ACDelco iridium spark plugs that will arrive next Tuesday can sit on the shelf until I put about 40,000 more miles on the car .

vettechictwins

dads new Z06 started this from the first week he had it. Bone stock. Happened with out any revs or anything. Although many opinions, one dealer tech said the alternator was faulty and the contacts in the alternator was periodically shorting. Who knows. One thing for sure it was all stock and appeared intermitingly.

Joe_G

^^good advice Clevite on that hot wire, I need to check mine and make sure it's tight and not against the plug wire....though my voltage is steady. My voltage will go low (always steady though) in bumper to bumper with the ac on but goes up right away when I start moving.

The Clevite Kid

Full of confidence I decide to drive the C6 to work today, nice day for a top-down drive. At the first traffic light just 0.1 miles from my driveway, idling for about 45 seconds, voltage steady at 13.8, DING-DING-DING, and a brief (one second or so) "SERVICE CHARGING SYSTEM" flashes on the DIC .

Nothing more for the rest of the 5-mile drive, including a 1 minute 45 second wait at a red light to turn left onto Bird Road (thanx, S Florida traffic "planners"). Voltage is still "LIKE A ROCK", but this does give me an excuse to install the ACDelco iridium plugs due to arrive on Tuesday, from Gene Culley, who has the BEST PRICE on the entire world-wide-web, by the way .

Joe_G

Swing by Roger's today and turn off the code. I'd do it for you but you'd have to spend $99 to license your car to my cord and that would be a waste since you're buying a cord.

Just save the brain damage.

Hope to see you on the 12'th at Palm Beach Raceway, full day of racing and evening challenge. I'll be there for the Challenge that evening as I've got family commitments during the day.

Wingrider

Enough of this. I talked to my tuner who said to take my HP Tuner program, go to engine diagnostics, go to the code p0621 (if I remember correctly) and change the "2" to a "3" and that will shut it off. I will do this tomorrow and be done with it. There is nothing wrong with the charging system, and probably never will be. This is a computer glitch.

The Clevite Kid

So I pulled the NGK TR6 V-Power plugs out, and put in ACDelco Iridium 41-104, a.k.a. GM part no. 12571165, spark plugs from Gene Culley at GMPartshouse.com (Best Price on the Internet, thanx Gene!). The TR6 and the 41-104 are the recommended plugs for the C6 Z06, one heat range colder than LS2 plugs, but correct for my 11.7 compression ratio and 500+ flywheel horsepower. The insulators on the TR6's coming out looked perfect, just the lightest coating of light tan deposits, just what you would want.

I also did a SERIOUS repositioning job on the alternator wire to get it away from the nearest spark plug wire:



For the NOOBS, the yellow arrow points to the relocated alternator wire and the blue arrow points to the spark plug wire. The alternator wire used to lie next to and touching the spark plug wire, and is now at least 3" away all along its length.

DRIVING TEST: 40 miles of stop-and-go traffic today, rock steady voltage and NO messages to "Service Charging System" on the DIC. I don't care which change fixed it, I am just glad it is fixed. For anyone suffering from these symptoms, I would recommend moving the alternator wire first (it is free!) and if that does not work, change to ACDelco plugs if you are running any other brand.

Anyone who thinks their car can run NGK TR6 plugs successfully can have the ones I pulled out with just over 1,000 miles on them, for $10 INCLUDING SHIPPING to the lower 48. Just send me a PM.

The Clevite Kid

Joe_G. did you ever reposition your alternator wire? Any results one way or the other?

Joe_G

Naa. I shut off the code a year ago or whenever it was and I haven't really thought about it since. Remember I like Occams Razor solutions.

I hate to say, but the common denominator seems to be the underdrive pulley, not the alternator wire. All cars have the alternator wire and most cars don't have this problem. Lots of cars with underdrive pulleys have this problem.

I hope yours is fixed.....if not...you're not far from having your own HP Tuners cord and solving this problem once and for all!