Hey Guys... I'm about to start breaking stuff here in Wisconsin out of frustration. 2005 Lr3 with the 4.4. I've been chasing a few error messages (CAN BUS lost communication and Parking A/B). The Alternator was charging at 14.6 volts but since the Lr3 has 77,000 miles I changed it out of caution. Bosch Alternator from NAPA.

Swapped it out today... Thankfully I had a voltmeter under the hood as my plan was to crank and check voltage at battery before I put the plastic shield and tire back on. Cranked it and immediately heard a whining noise at the alternator... checked voltage and got 18.5 at Idle. Acid/water started bubbling out of the battery overflow
and I immediately shut it down. Total run time was about 20 seconds I would say. What the F!!!!

I've been working on cars for 20 years and I know I didn't screw anything up here. The Alternator has a positive post and (1) plug. No way to screw this up.
This has to be a bad Bosch Alternator right? The whining tells the story for me. I've heard Alternator's whine like this when the Voltage regulator goes out.

Just to make 100% sure we have an overcharge I may disconnect the positive wire from the alternator and run a 18" positive Pigtail wire I have laying around
from the Alternator to my voltmeter and ground the Voltmeter tot he frame. If I crank and still get 18.5 volts... its a bad Alternator.

This pissed me off as now I have to pull the Alternator and go back to NAPA. Anyone else have this with Bosch Alternators before? The factory surely tests these
before shipment right?

Anyone see this before? I don't think I screwed anything else up... it only say 18.5 volts for 20 seconds.

 

Where is Wisco?

Anything can be bad, are you certain it was new and not a rebuild? A new BOSCH will be north of $350 with a rebuild around $200 - or about. But really it does not matter, I would not fire it up again. Remove and have bench tested. At least the alternator swap is not the most difficult thing to do, just a pain cause there is not much room. FYI the OEM alt is usually a Denso unit.

 

Hi... I am just outside of Milwaukee (Just to the West). The Saga continues as I yanked the Alternator and got bench tested at O'Reilly. 14.6 Volts and passed. So something with my Lr3 is causing the overcharge. Which is odd as the Alternator being replaced was charging at 14.6 volts just fine. I am changing as a precaution and since I have the inner Fender liner out (real easy access). I read if the (2) positive wires on the 3 prong plug are somehow contacting you can get a crazy overcharge like this. The plug looks good but maybe when I was changing the unit out caused the wires to chaff? Who knows. Any idea what the White Red Positive and the White Green Negative that go to the ECM do? Are they simply a positive and negative so the ECM can read voltage on the alternator? Or do they actually pass CAN data back and forth? Any idea?

 

The alternator is ECU controlled based on complex variables that could land a space shuttle on Mars. So that three-wire pug is very important actually. The regulator is PWM controlled by the ECU. I am not sure what happens if the plug is not plugged in or what could happen if damaged. I would think if plugged the alternator would default to some lower average output but there was another alternator thread and we suspected the plug, was not the case. So we did not learn much in that case. I will say I am surprised it put out 14.6 on the bench because that kinda rules out my suspicion that with that three plug connector off it would charge lower, like at 13.2. So now that I type and think, 14.6 must be default? Kinda high. Maybe unplug that connector on the alt and see what happens?

 

When I had my alternator tested last year the test setup at the auto parts store used the 3 wire control plug to mimic actual vehicle conditions.

 

Interesting since even the LR3 has two different style connections for the PWM signal.