I'm looking for a resolution to this problem. I have the same problem. P0622 and P0300 . Where is the PCM? Is the voltage regulator built into the alternator?

 

The PCM is on the passenger side inner fender. No, the voltage regulator is not in the alternator, it's in the PCM. If it fails, you have to replace the PCM.

P0622 - generator field not switching properly.
P0300 - multiple cylinder misfire.

Pull the alternator and get it bench tested. That'll at least give you an idea. Most alternators last about 125k or so.

I strongly suggest you treat the P0300 as an emergency. Continued operation can damage the catalyst. How are the plugs?

 

I failed to mention that I have the 4.7 Liter 2003 dakota. I just replaced the alternator with a remanufactured one 2 months ago when my headlights slowly faded to darkness on my ride home from work. The new alternator fixed that problem now I have P0622 2 months later. I find it hard to believe the voltage regulator is in the PCM because the post coming off the alternator and the plus side of the battery meet on a post on the driver side Power distribution / relay panel. as far as the P0300 I will change plugs right away - thanks.

 

Hard to believe or not, the voltage regulator IS part of the PCM.

New alternators can fail too.

 

Where can I buy a PCM for a 2WD 2003 4.7L, 5speed manual , if I need it? Alternator output IS fluctuating I'll have AdvanceAutoParts test it where I bought it in February. Any chance PCM is affecting P0300 multicylinder misfire? I already replaced plugs when I got P0308 code (cyl 8 misfire), a few injectors, cyl 8 coil pack, fuel injector cleaner, camshaft sensor and soon to try crankshaft sensor.

 

Forget about the PCM. That wasn't it. I had the receipt for the alternator and Advance swapped it out for me. When I put the new one in I realized how loose the belt was. replaced the tensioner. Alternator problem fixed. Still working on P0300 multicylinder misfire.

 

book recommends every 30,000 miles, its been way more than that. The gap should be 0.040 it was worn to 0.080" replaced plugs with NGK v power, running much better.

 

Glad you got everything fixed. Thanks for the updates.