Erratic voltmeter readings that vary from 12.1v to 13.7v
Mounted a known good VDO voltmeter tapping into the ACC fuse slot in the underdash fuse box. When driving the readings were 13.7v most of the time, BUT once every 2-3 hours, the voltage would drop to 12.1v for five-ten minutes before rising back up to 13.7. None of the warning lights come on at any time. My interpetation is that when it was reading 12.1, that was merely the battery voltage.
The Honda charging circuit is simple: the B+ thick red wire goes directly to one lug of a 100A fuse (#19 under the hood), the other lug goes directly to the battery. A four wire cable goes to the ECM.
Mechanics have installed another good alternator, serpentine belt, 100A fuse and B+ thick red wire with no change in reading behavior.
The vehicle runs normally, the battery is good and holds a charge, and in all other respects the car acts as it should. Am speculating that there might be an ECM component intermittent, but am loath to do a blind replacement without a specific cause.
What could be happening?
Welcome your analysis and thoughts
2006 Honda Element with 102,000 trouble-free miles