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.


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