Chrysler Repair: 2000 300M stuck in limp-in mode; where to buy parts, o reilly auto, output speed

Question
QUESTION: Hi, Roland.
Last night, my 2000 300M started to have similar transmission problems to the following cases you’ve helped with, and the onset sounds almost dead on to this one:

http://en.allexperts.com/q/Chrysler-Repair-807/2008/5/1999-300M-Trouble-shifting

There had been no signs of this, previously, nor did I hit anything, etc. that would seem to explain it. It sounds like it’s definitely the sensor, because the speedometer and odometer both don’t move and when I drop it down into auto-stick, it will be in first gear only when I first turn the car on, and it’ll automatically kick into second and won’t budge from there.

I just did the key on-off check and got the following codes:

P 1684
P 0700
done

I went to Autozone a few minutes ago and they only got the same readout and said that there wasn't a more specific code to offer me. I'm going to go to another store and try my luck there as well, but wanted to ask for your advice on this, too, since you clearly know your stuff.
Based on reading through more of your archives, it sounds like the other code is what would allow you to know what’s exactly going on to help. I’ll follow up with that once I can get it.

Any help you could offer me on this, including where to be able to find the part if it is the sensor, since Autozone said I'd have to go to a dealer, would be greatly appreciated.

Thanks so much,

Blake

ANSWER: Hi Blake,
The output speed sensor is definitely  a suspect but I would like to get an 0720 code before suggesting that you buy it. So do try to get another readout and if nothing yet, then if you can limp it along until another code appears that would be the best way to avoid unnecessary parts and repairs. Let me know if you get another code. As to parts, I would just try various parts houses in your area, but nationwide and local only establishments.
Roland

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

QUESTION: I just got back from O'Reilly Auto and they were able to dig up more specific codes. They pulled an 0500 and 0731. Based on that, he thought the output speed sensor was what was causing the issues. I went ahead and picked it up since it was only $20, but I did want to get your input on it before I follow up with a friend to try and do this ourselves or have my friend's mechanic help me out if it's something I can't handle.

Also, could you tell me what the voltage should be running from the wires into speed sensor?

Thanks so much for all of your help so far. You're an incredibly smart man and very helpful. It's certainly helped a stressful situation from not being worse.

Blake

Answer
Hi Blake,
I agree with replacing the output speed sensor. It is located on the driver side of the transmission very near to the end of the unit. There is a similar input speed sensor closer to the front of the transmission so don't mistake which one you are looking for. Lift a tab on the edge of the plug to relased the plug. Unscrew the sensor and make sure that the weather seal is reused when installing the new one.  The torque for the sensor is similar to a spark plug (20 foot-pounds). The dark blue/black wire is a ground to pin 13 of the tcm, the pulsing voltage signal wire (when the transmission is turning the drive shafts) is light green/white to pin 14 of the tcm. So check the continuity of the wires rather than looking for a specific voltage.
Roland