Car starts fine when it has not been driven. Once car warms up sometimes has issue clicks and nothing happens. After several tries it starts.
2002 Coupe new optima red top. Fully charged. Checked and battery cables are tight. New ignition switch 1 year old. Any ideas??

Thanks

 

First thing to check is the Theft Deterrent Relay. Its the HEART of the starting circuit. When you do everything necessary to CRANK the engine, can you hear that relay energize?? Its in the passengers foot well on the fire wall above the BCM. It has FOUR wires (RED, PURPLE, yellow and yellow /black stripe

The RED is 12 VDC 60 amp hot at all times. The Purple is the feed for the starter solenoid, the yellow is the 12 VDC (hot in CRANK) feed for the relay control and the yellow/black is the relay ground wire that is BCM controlled. When the BCM has all its security requirements met, it grounds that yellow / black wire to allow the relay to energize.

When the relay energizes, it connects the RED to PURPLE and energizes the starter solenoid. The purple wire is the solenoid HOT WIRE.

NOTE!!!! NUMEROUS C5s has defective starter solenoids. The solenoids hang up and fail to energize and allow the starter to function when you hit the crank /start position on the ignition switch

As weird as it seems, the next time that it fails to crank, you should get something that you can use to THUMP the starter. If you THUMP the starter and it cranks,, the solenoid is bad and needs to be replaced. On another NOTE, if the wiring connections at the starter solenoid are loose, corroded, burnt ect.. it can and will cause the SAME THING.

I used a 3 foot piece of re-bar wrapped in electrical tape to snake down through the headers and THUMPED the starter when mine was going bad. Got me out of a jam several time until I was ready to do the repair.

Bill