Ok, so last fall just prior to putting car up for the winter I hopped in it to go to work, went a block and got “service charging system light”. I looked at the gauge and it verified the car was not charging. I turned around and put it in the garage and drove my truck. I assumed the alternator was bad so over the winter I ordered a replacement. I put the replacement on, still not charging. For giggles I took the old, original alternator and had it tested, shop says it was still good and was putting out a charge. Hmmm. Ok, gave the car to my son (who is very familiar with C5’s as he also has one. He removed the Remy replacement and reinstalled the original alternator. The car showed as charging for a little while then stopped again, almost like something told it to stop charging?! My son diagnosed further…found some resistance in wire from alternator to starter that shouldn’t be there. He ran a separate wire from alternator to starter…car started charging again. I told him to drive it a little and make sure it was good. He called me later that day to say now the car went into limp mode and kicked a p1518 code.
I am a bit baffled here. Battery is good. I’m not a tech (my son is) but it SEEMS both these conditions may be related? Both seem data related? All grounds have been checked…we have not touched ignition switch.
not sure how to proceed here…don’t want to throw parts at it. Any of you versed C5 guys have some thoughts?
Any help would be greatly appreciated.

 

Could just be a low voltage condition caused by the bad connection from starter to alternator. The factory wire from starter solenoid to alternator has a fuseable link, GM designed this in case the alternator shorted to ground and full battery power would burn up that wire and start a fire, just saying.

 

A P1518 can be caused by a weak battery…I would check all of the TAC modules power and grounds and also the Serial Data wires which are on the (16 pin connector) C2 connector pins 12 and 13…tan and orange/black…check the Throt Fuse and well as power to both sides of the TAC motor…

 

Thanks for the input to both of you. I will pass this info on. Both fusible links are good. any additional thoughts appreciated! I’d really like to give my truck a rest and be driving this car!