Just posting this to share incase someone else has the same problem.

Symptoms: Speedo reads +mph when sitting in drive, reverse with foot on the brake - usually showed between 10 and 25mph on the speedometer. Car 'clunked' when shifting into reverse and would feel like it was pulling hard against the brakes with an elevated idle.

Took it to AAMCO, and they replaced an output speed sensor (~150$). 4mo later, same thing, and I take it back. This time they say the code isn't there, and they can't reproduce the problem, but there is the generic transmission code P0700, and it is clunking into gear, and the fluid smells funny, etc, and they try to put the hard sell on me to pull the trans and take a look (700$ to take a look). I told them no thanks.

Brought the car home, bought a code scanner (been needing one anyway), and sure enough, code P0720, output speed sensor. Bought one at autozone for 16$, replaced it myself.

Several weeks later, same condition. Dropped the trans pan and changed the filter/fluid because there was some metal dust on the magentic tip of the speed sensor. No dice.

After messing with the car for a while, I realized it would only do this right at startup, and then the condition would go away, until I turned on the air conditioner (summer in phoenix so this is always on may-oct) or the headlights.

Had my charging system checked, and they got a "Excess Diode Ripple" condiiton on my alternator. Picked one up from the local auto recyclers for 40$, and now the car is running great again with no p0700 or p0720. It turns out that when a diode in your alternator goes out, it can create basically EMI that can freak out various sensors in the car.

So much for the shot transmission and 700$ to take a look. If I would have let them do that they obviously would have rebuilt it costing me thousands, and I would still have the same problem. Lol AAMCO, and yes, they will be hearing about this.

Also, one note, when the condition would happen, it would throw codes p0700 and p0720. Once these codes were thrown the trans would shift bad, harsh from park into reverse. Pretty sure the car got stuck in limp-home mode once, but all of this would go away when I used the scanner to reset the CEL.

Anyway, hope this helps someone else and saves them some $$...

Oh yea, one side note, the alternator job is trivial, except for the belt tensioner, which was a total freaking nightmare. Get in there and figure out if you can get a tool on it before you tear the rest of the car apart. I had to use a 3/8in socket driver, but a normal ratchet wrench was too big, so I used one that was just a bar with the 180* swivel, that was the only thing compact enough to get in the tensioner, I then had to use a piece of pipe to get enough leverage, pushing hard with the left hand, holding the tension off of the belt, while getting the belt on 1 handed, and this was from under the car. I wasn't sure I would be able to pull it off, and it was a challenge. Im sure there is a better tool for the job, but I didn't have it...

 

There have been a lot of issues with bad grounds on these cars. MAIN grounds not little ones. There is one over on the drivers side down in front on the side that pulls out and falls back in depending on the engine tilt...lol. Talk about a PITA to find the first time. I generally DO NOT enjoy working on Pacificas.

 

Travis,
I would like to give you a big thank you for this post. By far the best one out there regarding this issue. My car just turned the 100,000 mile mark and prior to that i always wondered if i was going to have the dreaded tranny issues you always hear about. Well last week i noticed my batter light came on. no biggie, seen it happen once before. It went out, and when i got home i check the battery voltage and it was low, like 13v to 13.2, but the light was out. I continued to drive it, well a couple days later the car started shifting weird and when coming out of park the speedo needle would go up to 15 or 20 mph. So, i put the scanner on and of course it gave the 0700 and 0720 code. Bought a new output shaft speed sensor, replaced, was good for a couple miles, then again the problem reappeared. Talked to a tranny guy by the house and we talked about metal on the sensor. There was none on the old one. So, i pulled out the new one to make sure, none on it either. I looked in the hole with a mirror and light, all looked good. So, once i checked all the ground connections and reading your post about the alternator, i went ahead and pulled the alternator from the car and had it tested at Autozone. And low and behold it failed the both the rectifier and stator portions. Replaced with a new one $225.00 with core, and the car now operates perfectly.

 

Thanks TravisAZ,

I have a code P0700 as well as P0562 (charging system voltage-battery low) and PP0441 (evap system). I had a fuel pump replaced (the primary), and upon return, the CEL came on. My AC doesn't blow cold air, the fuel gage shows E at above 3/4 full and will not accept more fuel.

I will get the alternator checked out and replace my tarnished/corroded grounds. I've replaced it once before and had the same challenges with the tensioner that you described. The next time that I do this will be in the Auto Craft Shop with engine lifts/supports. That takes a lot of the pain away, being able to jack up the engine. This can be done with a floor jack as well.

This post has been the tip of the day for ME...thanks!

 

I wonder if this is our problem too....?
I thought the car might have a tranny problem since I bought it 3 years ago... It would shift hard into drive or reverse sometimes, sometimes on flat ground and especially sitting facing downhill... Well, I had to replace the 1st battery, my husband killed it a few times listening to CDs while washing car... but the new one has also died easily, like the mechanis was working on the car and no lights left on, but doors open here and there, so lights here and there... and we were all puzzled saying hmm time for a new battery... The alternator is making noise, sounds like the motor or w/e makes it turn the belt is going bad and there is rust dusted all over to the left and right side of it... I think my dad said the bearings may be going bad... wonder if getting a rebuilt or new one will fix our problems....

 

Oh... only thing, to my knowledge I have not gotten these codes... and I say to my knowledge because the P0440 one has been on since i got it basically...

 

Looks like I've got the same issue. We have a 2001 T&C LXi 2wd 3.8V6 and have been experiencing weird speedo issues for the past year along with the hard shifting. The worst was always at idle while stopped with the transmission in drive. The speedo would jump up to 20 and the transmission shift gears while sitting still.

I did the same and replaced the output speed sensor twice with the same results, it would work fine for a while but the issue would return. After reading this post, I started checking the alternator. Sure enough, it seems to be bad. I first checked with a multimeter and watched as it was outputting AC current at 5-35 volts but the DC stayed at 13. The auto parts store was unable to perform a complete test so I disconnected the field wire connector from the alternator. The transmission and speedo worked perfectly. When I plugged it back in, the problems resumed.

I have a NEW alternator on order. The one I have now will likely be my last rebuilt one!

 

My wife drives our Pacifica most of the time and the other day she told me that the speedometer started jumping up to 20 MPH when in park or at a stop. First I thought she might be confusing the tach with the speedometer until I saw it for myself.

I got into the car, started it up and watched carefully. Within a few seconds of starting the car the engine began to rev up a little (1100 RPM) and the speedometer went up to about 20 MPH. Also the engine light was one. Stepping on and releasing the gas peddle didn't help. Put the car into Drive with my foot on the brake and immediately noticed the car started pulling forward. I had to press harder on the brake to keep the car from rolling forward. I also noticed a high pitched whine that would go up and down with the RPM of the engine.

Without moving at all, I could hear the transmission shift into 2nd gear and after about 20 seconds it shifted into 3rd. The car still hadn't moved from where the car was parked. I moved the shifter into the manual shift position and tried to downshift back into 1st gear but it would not change. So I shut the car off.

My 2nd try, I started the car and similar results occurred. This time the transmission stayed in 2nd gear and I was able to drive forward. The car drove fine down the road, shifting normally beyond 2nd gear. Bringing the car back to a stop caused the engine to rev up again to about 1100 RPM and the speedometer went back up to 20 MPH while stopped.

I test drove the car around town this way and tried turning off the engine a few times to see if the issues would go away. I brought the Pacifica back home and started my research online.

The following day I got back in the car and started it to see if anything had changed. Once the gauges and lights settled down the engine light stayed lit. Also the battery light came up which raised my suspicion that this might be an electrical issue. I drove the car around a short while, stopping and starting it to see if the symptoms would change. Sure enough the battery light went off.

I brought the car to Autozone and asked them to check the error codes. They said the engine light was an O2 sensor which I doubt would cause the revving/speedometer issue. Afterward I asked them to check the charging system. They brought out their special meter and ran a series of tests. The end result they said the battery was perfect as were all the voltage numbers however the alternator was fluctuating irregularly.

I plan to replace the alternator and will re-post my results.

 

rbeckler and BubbaSmith123: Did the alternator fix your problems?
I have had 700, 720 (and sometime 731/732) codes and erratic speedometer behavior for months now on my 2003 300m. Got my charging system and ground connections checked after showing Firestone the posts on this thread...no problem found there. So of course all they could suggest was to change the input and output speed sensors first, and $350 later no change.
I don't want to spend a fortune guessing, so I'm hoping someone can suggest a better way to narrow this down... or if the alternator needs to be removed to detect a bad diode if the electrical system does not typically involve taking it out of circuit. Other posts suggest a possibility of the solonoid pack, PCM and TCM.???

 

Replacing the alternator did the trick. It's been fine since July. No Speedo issues and transmission shifts smoother than ever.