First check the serpentine belt tension, (with the engine not running). If that is okay, suspect a defective diode in the generator. A professional load test will identify that by the most output current it will deliver is exactly one third of its design rating of typically around 90 amps, and "ripple" will be very high.
Due to their design, it is common to go through four to six generators in the life of the vehicle. If yours needs to be replaced, to reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. As they age they lose their ability to dampen and absorb the huge voltage spikes these generators produce. Those spikes will destroy the internal diodes and voltage regulator and can interfere with engine sensor signals.
Saturday, December 22nd, 2012 AT 11:14 PM