I have a 2006 F-350, Lariat FX-4, DRW with a 6.0 Liter diesel engine. For the last several days, I have had an intermittent problem with the idiot light for my charging system activating. Sometimes when it comes on, it stays on for 20 minutes and then goes out. Other times it only stays on for a minute or two. There is no distinct pattern to it other than it seems that when it does come on, it never stays on longer than 20 minutes with 5 minutes being the average. Both batteries are from NAPA and only 1 month old. All connections to the batteries and alternator are clean and tight. Voltage checks on each battery by itself (cables disconnected) show 12.6 volts and test good under load at NAPA. With the engine running at idle speed and the idiot light off, voltage checks at the battery are between 13.5 and 13.6 volts. With the engine speed increased to a steady 1900 RPM voltage reads 13.7 to 13.8 volts. When the idiot light is on the voltage is also at 13.6 volts at idle. I have not been able to test directly from the alternator and I have not tested at increased rpm when the light was on. Belt is in good shape and pulleys seem to be spinning normally without any abnormal noise. I do not know the age of the alternator but it looks bright and shiny and doesn’t look like it’s been running hot. I have not had any problems starting the engine and when driving at night, the headlights seem just as bright and steady as they should be. Is this just a weak alternator or could it be something else. I would think that the voltage should be reading around 13.8 to 14.2 volts at idle and that there might be an issue with the voltage regulator. Is there an alternator rebuild kit available so that the regulator and brushes can be replaced without replacing the entire unit (like the old days)? Any thoughts on this would be greatly appreciated. Thanks! Zeus

 

I cant believe no one has chimed in on this!....Maybe I should have posted it in the 6.0 Powerstroke Diesel forum?? How do I move this over? Thanks! Zeus

 

I would like to hear some answer to this .The co. i work for has 04 f350 6.0 and it does the same thing on and off at any giving time.

 

I would say your alternator is shot. Replace it, or you'll be looking at replacing your batteries again. I've heard low voltage also messes up things in your diesel motor.

 

I've never completely understood the logic in the voltage regulator that turns on the warning light. Just that the VR thinks there is a problem. You're voltages are good with the light on and off, so it would seem like your alternator is OK. But still the VR thinks there is some problem or it wouldn't be turning on the light.

About the only other thing I can think to suggest to test is for a bad diode. If you have a decent quality DVOM, set it to AC volts, put the black lead on the battery ground terminal and the red lead on the B+ terminal of the alternator. And see if you read AC voltage.

If your alternator is putting out AC voltage, then you probably have a bad diode and need a new alternator. Just be aware that some DVOM's can mistake the pretty unstable output of a perfectly good alternator for AC output. You can test your DVOM on a vehicle with a working alternator to get a baseline.

 

The intermittent charge light is usually a sign that one or more diodes in your alternator are bad. There are 6 diodes in your alternator arranged in a ring pattern. They rectify the AC voltage, or change it to DC current.

If you put your radio on the AM band, and either on no station or on a very weak station, with the engine running I bet you hear static or a hum. That static or hum will change with the engine speed, the frequency will increase with engine speed. If you take off your antenna, you'll still hear that hum. That means the static is on your power lead, not your antenna lead. This is also an indication that your alternator has one or more diodes that failed.

 

Thanks! I've ordered a new alternator and will replace it. Nonetheless, I am curious as to why this problem is going on. My meter is a Fluke 187 and should have the capability to check this. I have noticed that the noise level on my CB radio has increased as well. I'll check the am radio noise level too. Thanks for the input!

 

Before changing the alternator check the plug. They are know weak link on those trucks.
I had intermittent light on new rebuild alternator for 3 months, yet the sucker passed bench test. Than it died 150 miles from big city that would have replacement alternator.

 

Thanks for the troubleshooting tips, I did that with my Fluke 179, no AC. I've had the same issue going on for a few months, the Batt light would flash for seconds or for 5 min, I found that both batteries had low voltage when they sat without a load, and barely move under load. I had a diesel shop look at it, they tested the system, the batteries each have a failing cell and the alternator is strong. Just for kicks, I had a local parts house run their curbside test on it, same results. Here's the awesome part; according the Motorcraft date codes, those are the original batteries from 2003, I cannot complain.