92' shows a code 16 and 31

I have a 92' Park Ave (base model) A few weeks ago my dad was borrowing it, and he called telling me that the car suddenly would not shift while he was driving. It would run, but the transmission seemed to be stuck in high gear. This wasn't all that happened, as he pulled into the driveway, he noticed that it was running hot (coolant temp. light came on) When I got back into town to check it out, I got 2 codes, a code 16 for high system voltage and a code 31 for the PNP switch/ circuit. A long time ago it had the code 31, but no apparent engine problems. I replaced the PNP switch to be on the safe side, but the code still comes back. As far as the system voltage, I replaced the alternator, checked all battery cables, etc..but that didn't fix the problem. Does anyone know if the code 16 and/ or 31 are the cause to the problems we're experiencing? Any help is greatly appreciated, thanks!

Lowke
BTW..The battery in the car is only a 650 cold cranking amp, could the problem be because the battery's not powerful enough?

Code 16 System High Voltage

If the voltage is above 17.1 volts for more than 2 seconds, the Service Engine Soon light will illuminate. Have the charging system checked; you could have a bad regulator in the alt. I have seen quite a few replacement alts that may test ok on the bench, and then fail in the real world. If you’re getting "spikes" up that high, it could effect every component on the car.

Code 31 Park/nuetral switch

Check all connectors, and for a faulty switch. That is all there is on this one!

Code 16 System High Voltage

If the voltage is above 17.1 volts for more than 2 seconds, the Service Engine Soon light will illuminate. Have the charging system checked; you could have a bad regulator in the alt. I have seen quite a few replacement alts that may test ok on the bench, and then fail in the real world. If you’re getting "spikes" up that high, it could effect every component on the car.

Code 31 Park/nuetral switch

Check all connectors, and for a faulty switch. That is all there is on this one!
Thanks for the help, I had the original alternator tested but it tested ok, but autozone replaced it for free anyways.. and so thats 2 alternators and 2 regulators with the same problem. When I get a chance I'll see about replacing it again..
I forgot to ask earlier, would it be alright to install the 140 amp alternator (for PAs with heated windshield) even if mine does not have that feature? I'm going to be running an amp and lots of other power accessaries but I don't want to damage anything in case the load is too high for my charging system. The current alternator is the standard 104 amp. I figured if I change it, might as well get the bigger one?

Good news! My overcharging problem seems to have been caused by a faulty battery. I switched battery's out with my fiancee's Saturn and the volt meter needle finally came down and the car ran fine all day. Now I just wanted to ask you all how powerful of a battery should I get? The bad one was a 650 cold cranking amp, but I think that it was underpowered for a loaded PA. I had an Interstate battery once, and I loved it! I don't know how many amps it cranked, but it lasted for years without any problems. Anyone have any advise on any other battery brands/ amperage I should get now?

You want CCAs to be bare min. 2 1/3 x the motor's cubic inch size, so with a 3.8L you have 231 ci. thus needing a cca rate of atlest 231 x 2 = 462. 550 cca bare bones, But that's not going to do you a whole lot of justice on a cold Chicago morning I'll tell ya. 650 is right, there are duty cycle ratings for higher amp charging systems, like "X-XA or X-XL" on the label somewhere? This is where it get's grey for me. I'm not an electrician, so someone else should straighten that out for ya.