Voltage from PCM to Alternator on '04 2.7L Sebring Convertible?
 

I'm stuck. Battery light came on. Limped home. Had alternator checked -- was OK. Battery test -- OK. Battery cables and connections seem OK. Car starts and runs fine right after I take the charger off the batt, then declines as the batt volts go down (natural if alt isn't charging). I did the key flip thing to get the codes. (Yes, I should have done that before taking out the Battery and Alternator. I just was sure one of them was the culprit.) The code I get is P0622 -- "Alternator field circuit open or shorted." I checked continuity from alternator plug to computer connector they're OK. The dark blue or black wire with the yellow or white stripe from the alternator plug (not the green one) showed continuity with a bunch of socket holes on the connector, which baffled me, until I unwound the harness a bit and found that several wires are connected in the harness bundle.

I tested the voltage at the alternator plug while running. Both wires showed the battery voltage. Weird, I thought. Since the green is supposed to control the alternator by ground, I thought the voltage would be zero at the green wire. Evidently not. Figured the internal voltage regulator in the PCM was shot, so I got a PCM from the junkyard (along with the matching key, cylinder and the theft prevention antenna ring thing). I swapped all that in, started fine -- still not charging.

I tried the bypass with a firewall mount voltage regulator from a Dodge pickup that several web pages say will work. It doesn't. It did prove the alternator works, though. With the bypass, it briefly put out a battery cooking 15.7 volts before I disconnected it.

After reading a bit online, evidently the wires from the PCM aren't energizing the field magnets on these Chrysler alternators directly -- only prompting. Does anybody know what the voltage range is supposed to be between wires at the alternator plug?
Does anybody know of an alternator swap-in that would allow the external old-style voltage regulator to work? I don't care about the engine light staying on and Illinois doesn't have vehicle inspections. I just need to have this car to drive before it snows.

In a last attempt, I got yet another computer, key, etc. and another alternator from the salvage yard. Put them in. Still no luck.

Thanks for your attention, and any replies!
MoparJJ

Have you checked and cleaned the Negative (ground) from battery to body and engine connection points? They may look and feel tight, but can corrode and insulate an actual good connection(too much resistance electrically).

When you bypassed it were you using the original wire or different ones?

Thanks for the reply
 

The resistance to the engine metal from the underhood negative post is very low, so I don't think that's the issue. I've had the battery out and cleaned its terminals. I haven't messed with the engine ground, but I did attach a jumper cable to the case of the alternator, and to the ground post under the hood. Suppose I should try that jumper cable bridge to the negative battery post directly. I'll try that today.

Thanks

Thanks for the reply
 

I used a connector off of a wiring harness in a matching car found in the junkyard. I snipped it off of the junker's harness, leaving about 6 inches of the 2 wires. The junkyard connector was spliced to wiring leading to the external voltage regulator and wired according to the online diagram. I wired a good ground wire to it -- to the bolt that I used to attach it. The connector was put on the alternator in place of the one on the engine harness.

Thanks