Chrysler Repair: charge light, codes 21/46: 3.3L , chrysler voyager, field coil

Question
QUESTION: My 1997 Chrysler Voyager 3.3 V6 (in Sydney, Australia)has done 175,000 km (around 120,000 miles). Starting from last December, the charge light would come on every now and then when the car is running. Before the charge light comes on, the light on the dash board will start to flick. After turning the engine off and restarting again, it will go off. It is especially true when I have parked the car for a few days in the rain. I have tested the alternator by running the engine and turn the head lights on and disconnect the battery. The car keeps running and the lights will not dim. Any advice on what I should check? Thanks and cheers for now. Lim

ANSWER: Hi Lim,
Try the ignition key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the check engine light, which remains on, to see it begin to flash, pause, flash, etc. Count the flashes before each pause. Then repeat to assure accurate count. Then tell me the counts in order appearance and we'll go from there.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hi Roland, I had a mechanic check the wiring of the O2 sensor, and he said that the wires did not look loose and he changed a new upstream sensor for me about ten days ago. (I had changed the downstream one at the end of last December, after the charge light had started coming on). However, the charge light still comes on and I tried to obtain the check engine light flicking pattern. This time is 1 2 4 6 5 5. Can you tell me what it means?
Thanks in advance and have a good week. Lim

Answer
Hi Lim,
The 12 comes up regularly because if the battery is disconnected it is sensed by the pcm and reports that power loss as a fault. The 55 means 'end of code readout'. So the only relevant code to this problem is the 46 which means that the voltage output of the alternator is higher than the system is supposed to be running. It means either that the dark green wire from the alternator field coil that runs from the alternator pin 2 to pin 4 of of the powertrain control module is shorted to ground or that the field coils of the alternator itself are shorted to ground. So if you pull the 2-wire (3-pin) plug at the alternator and measure both the pin and the pin socket as to what they show as the resistance to ground one of them will show 0 ohms are very close to that. If both are reading more than 5 ohms then try shaking the harness for that wire to see if you can induce a short. The voltage is controlled by that wire being oscillated on and off ground by the logic control of the pcm to produce around 14V output, but if the wire gets grounded or the field coil of the alternator develops an internal short to ground that will cause this code. It also will turun on the check engine light and possibly also the charging light. At least we ought to get rid of the 46 code and see if that solves the charge light. It is interesting that first it was the 21 code which implicates the 12v supply wire to the alternator, and now the 46 code which implicates the other end of that same field coil wire. It may vell be that the alternator itself is faulty in having a field coil that is shorting to ground at several locations. If the dark green wire seems to not be shorted, then I would suggest getting the alternator rebuilt or getting a rebuilt unit at a parts store.
Roland
PS Thanks for the earlier rating and nomination. You are entitled to go through the same rating process for this answer if you believe I merit it. Thank you