Intermittent Check Charging System and Fault Code P0620

[jt_armstrong]

I keep getting "Check Charging System" warning light coming on. It has been doing this for over a year. Very intermittent and its off almost as quick as it comes on but recently it has been coming on more often and staying on for maybe 10/secs or so. Today it logged a P0620 fault code which doesn't appear to help much. I did find reference to TSB 17738 but I can't find out what this TSB recommends to resolve the issue. Anyone else had this?

 

[TJs98GT]

Usually thats a bad alternator. Their is an updated voltage regulator available for those trucks. Some of the reman alternators you get from the parts stores may not have the updated part so its best to go through Ford for this one.

 

[jt_armstrong]

Is it possible to change out the regulator or do you have to do the whole thing?

 

[TJs98GT]

Typically it is built into the alternator. Run the truck over to have a free charging system test done. Most auto parts stores offer that.

 

[jt_armstrong]

Recently the fault has stayed on long enough for me to actually measure the alternator output and I am not seeing anything unusual (approx 14.1v) It doesn't appear to change with the fault condition. That why i was interested to see what the TSB recommends but I can't find the details on that.

 

[stamp11127]

That code comes up as a generator control fault. I would check the connections at the alternator and trace the harness back checking to see if it has rubbed on anything.
Regulators are replaceable but it becomes a cost decision if it is justifiable to only replace the one part in an old alternator. The brushes are usually near the limit also. Most of the time it is better to replace the alternator just for the warranty. You should find the fault before condemning it though.

If there is a shop that can test the alternator output while it is still on the vehicle that is the preferred test to taking it into an auto parts store. They have the ability to load the electrical system so that it forces the alternator to output at its max limit. You can perform the same test if you have the toaster type battery tester and an amp clamp for your DMM.

Regulators cycle on and off hundreds if not thousands of times a second. A DMM or volt meter doesn't capture readings fast enough to display an error in the cycling unless it is a major failure.

 

[TJs98GT]

Yeah, you will need to do more than just an idle test.

 

[jt_armstrong]

Just to close out this thread, I eventually purchased a new alternator off ebay. Swapped it in and it has worked a treat ever since. No more beeps or warning messages.