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Can water under the back seat cause a charging system problem?

We had a torrential rain monday. The car was parked in the driveway.

yesterday (tuesday), I was driving my 2002 Bonneville. I had completed several errands, and suddenly got a “Check Charging System” error on the display. The voltmeter, normally above 14, was showing no volts. I stopped the engine, then tried to restart. The engine started, and the meter showed about 11 volts. But the car ran normally, and cI completed two more errands. Then I took the car to Interstate Battery, since I knew the battery was over 5 years old.

The man diagnosed a bad battery and replaced it. But we found about half an inch of water under the back seat. And the problem did not go away. It continues to give me the warning when I start the car. But the car starts normally. If I take it on the highway, the voltage comes up to normal.

I went to Auto Zone fir the free charging system diagnosis. The meter showed less than 8 volts at the jumpstart point under the hood. We tookt the back seat out, and found the voltage at the battery to be 12 volts (engine not running).

Can the water under the rear seat (where the battery is) be causing this problem?

I think the water is from the sunroof drains not working properly (a separate issue).

I’d fix the drains … the water can start to smell and be difficult to remove. You will get mold and mildew growth.

The problem is probably corroded cables or connections. If you have a 4 volt drop, there is a bad connection somewhere between those two points, or in the grounds.