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Alternator or PCM
Posted to Technical Discussion Forum on 7/15/2017 11 Replies

I have this currently in tech help and while the consensus is faulty alternator which I am inclined to agree with as the pcm looks like it is trying to control the charging before setting the code P0625 : field circuit low , [2008 Ford Taurus Limited, BATT/Charging/Starting Waveform] I'm not fully understanding exactly what may be wrong as some of the responses have been it may take more than one attempt to get a good alternator. There are no charging issues and voltage is stable. One respondent mentioned looking at AC voltage which I did while running and was not excessive, but not during start up and here is what I captured after starting engine, Blue trace is now AC voltage, 2 volt scale [2008 Ford Taurus SEL, BATT/Charging/Starting Waveform] . I then wanted to see what would happen while commanding voltages high and low. [2008 Ford Taurus SEL, BATT/Charging/Starting Waveform] Could this be the cause of the code and how would one check this before installing if indeed this is the fault of the alternator? One other thing I came across in more than one source, including Pico under the Ford smart alternator test. Not to install a lead-acid type battery on these systems( which this vehicle I suspect has, Interstate Mega-tron), but it notes it could do damage to the battery because of the higher voltage strategies. It lists a silver calcium battery. Scott Hinkle linked me to his discussion, but not sure same issue, his seemed to be an unstable charging voltage which turned out to be a faulty or sub standard voltage regulator which he rectified :), with a member supplied quality unit. Welcome any and all comments, thanks.

Paul Sanders
Owner/Technician
Parkway Auto Rebuilders
Harvey, Illinois, USA

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car Vehicle Data

2008 Ford Taurus SEL 3.5L

Engine3.5 L
Trans6-speed Automatic (Electronic)