P0720
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Laughing Gas
Joined: Feb 2014
Posts: 1,041
Likes: 72
From: Springfield
P0720
It started off every great now and then the code would show up but not its every time i drive my truck. So long as I’m moving it doesnt show up but if i stop for more than 1 or 2 seconds the code pops up and screws with my truck till i get going maybe 10mph. I now what the code is for, fault in the OSS circuit, but is is possible for it only to appear like it is? Ive searched some and couldn’t find much help past what the code says. I did read one thread where the guy’s alternator was actually bad and it caused the code, another had a bad coil on a v10 causing the same issue. I have noticed my charge level fluctuates now where as i dont remember it changing near as much before. Is it possible my alternator is still kinda functioning right but is screwing up and causing electrical interference causing my code? Or is there somewhere else i should be looking? Hopefully someone can help me get this sorted out soon, the trucks due to be hooked to a heavy dump trailer soon
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,730
Likes: 2,658
From: SE Florida
Alternator problems can definitely cause this. If the rectifier circuit is bad you will get an AC component in the DC that should be there. The PCM sees this as a speed signal on the OSS and other speed signals. An oscilloscope will tell the story, as will a high end alternator tester.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,730
Likes: 2,658
From: SE Florida
You could bring the truck to a shop to test it. I have a tester that can test this on an alternator. It clips onto the battery clamps. I don't know if a parts store can test the rectifier circuits or not.
It's a Van Gogh
Joined: Feb 2010
Posts: 7,813
Likes: 1,335
From: Elk Grove, CA
Alternator problems can definitely cause this. If the rectifier circuit is bad you will get an AC component in the DC that should be there. The PCM sees this as a speed signal on the OSS and other speed signals. An oscilloscope will tell the story, as will a high end alternator tester.
Is that the kind of rectifier problem that can be felt on a cold engine? As in engine is cold but alt is warm?
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,730
Likes: 2,658
From: SE Florida
I've never been able to feel a rectifier problem. I can see it in an oscilloscope, but it doesn't produce any feel that I can detect.
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Laughing Gas
Joined: Feb 2014
Posts: 1,041
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From: Springfield
What would be a good replacement alternator if that is the problem? I don’t run many accessories on it but do have a plow I’m looking to set up and a winch for when needed. I looked at prices for stock amp level and it seems I’d be better off buying one with more output
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