My 2000 intermittantly goes from not charging (11.5 - 12V) to overcharging (15.5 - 16V). It also sets the P1637 L-terminal code.
Then it suddenly heals and moves to normal (13.8 - 14V).
I took correlating readings at the battery, so the gauge is reporting accurately.
It's the French model, maybe this wishy-washy behavior is normal - Ha.

Could this possibly be the old Optima battery causing this sporadic behavior? I have been letting it sit for long periods (2 weeks) lately, and I have expected the battery to die on me. But it starts fine and seems to hold a good charge at 11.8 - 12V. I trickle charged it yesterday, but the weird alternator behavior continued today.

Should I check the grounds, connections, etc; before I panic.
Which ground connection would be the guilty party for the alternator L and F terminals? any other advice?

tks,
DG

 

It sounds like the weak battery is loading the alternator until it is charged up. I would put a charger on the battery for a day and then see how the alternator functions.