You did not state what model you have and also if it is stock or if mods what they are
You need to use an error code reader, or OBD-II scanner or GM Tech-II and report here if and what the DTCs are
Also need to look and report if anything shows up on the DIC such as
Some owners of a 2005-10 Corvette or 2004-09 XLR may comment that the Service Charging System message displays on the DIC. DTC P0621 is stored. This may be a result of aftermarket spark plugs or an open in circuit number 2540.
1. Check for aftermarket spark plugs.
Plugs that are designed with a "pulse" technology may interfere with this circuit and cause the Service Charging System message in the DIC and/or P0621 DTC to store in the ECM.
If aftermarket plugs are installed, replace the plugs with OEM parts.
This is not considered a warranty repair and all cost associated with this repair should be the customer's responsibility.
2. Circuit 2540 is supplied voltage from the horn fuse, position 2 in the UBEC.
Try the horn to see if it works.
If the horn does not work, suspect an open fuse.
This fuse may open if the horn is shorted due to water intrusion.
If the horn is functional, check the integrity of circuit 2540 between the UBEC and the generator.
Refer to SI document 1481125 for the schematic. Repair circuit 2540 as needed and re-evaluate the customer's concern.
Also check the main ground wire from frame, directly to I think, back of engine
There was some issue but cannot recall which C6 years when the connectors of wires going to battery posts
had weak crimps so have someone move the wires at the battery posts and someone watching the dash gauge and see if the voltage level changes
IF the C6 has been in areas of lots of water
On the frame there are ground splice packs, 2 of them are below headlights on frame, so see several ground wires going into
those packs
Water getting in them cause all those ground wire connectors to corrode and cause ll kinds of odd problems
Check the wiring and their connectors of the Alt to the battery and the PCM as being clean and tight
wiggle wires and watch voltage gauge
