I have an 03' Grand Caravan Sport, and the battery light came on while my husband was driving to work yesterday. When he went to leave it would not start, so we replaced the alternator with a used one. When he first tried to move it after replacement, it would not move at all for a few seconds. Once it did, it now shifts hard from park to drive, the motor moves a lot at the same time, and the power door and power rear gate don't work like they should...only one at a time works(if one is opened with the button, the other won't) and the FOB won't work at all. He thinks he might have tightened the bolt on the tensioner too tight(he loosened it before he realized he didn't have to) and one of the other pulleys too. Could it be the alternator? The battery? Something else? The motor mounts look ok, and there was no movement in the motor before changing the alternator. There are no warning lights. Also, when you put it in drive from park and sit still, the serpentine belt flutters badly at the bottom between the AC compressor and the main drive pulley, and makes a humming noise until you start moving...then it's fine and the speedometer jumps between 0 and about 20mph. Any ideas?

 

Did you get the belt routing right? What size engine?

 

yes, got the routing right. It has a 3.8 in it, not the original engine. It was replaced, but the dealer had no documentation of it. I said it moves when you shift from park to drive... there is now a pretty bad thump, and the entire engine moves 2-3 inches as it shifts into drive. It doesn't do this any other time, only from park to drive, and when you first start to move it will sometimes lurch a little. It was not doing any of these things before changing the alternator. Now, since this van has the power side door and power lift gate, does it need the 160 amp alternator rather than the basic 136?

 

We just went through something similar. Ours is the 136 amp but our does not have the power slide doors or any of that. Our mechanic told us that if we did have all that we would have needed the 160 amp for our 2002 dodge Caravan V6, 3.3L. So, I would venture a guess that you have the wrong amps for your van's power needs and an bad or wrong alternator will cause all kinds of havoc with shifting and the speedometer if it doesn't have the enough power. Hope this helps.

 

Sounds like classic AC ripple from leaking diodes in the alternator.

 

How would I go about finding out for sure? The alternator is putting out the correct amperage, the battery is now charged and holding like it should, and now the doors work again. We ran the in-dash diagnostics yesterday to pull the codes from the dash and got P1684(disrupted power to TCM), P0455(large EVAP leak), E100.3, E100.5 and E400.1. Disconnected the positive battery terminal this morning for about 15 minutes in hopes of resetting the computer, but if it did, it didn't fix the lurching/speedo problem. My husband just went to OReilley's to have them scan it to see if any codes come up. On his way home today, it started out in 2nd gear and would not shift out of 2nd until he pulled over, shut it down, started it again and drove about 1/4 mile...then it was fine and shifted like its supposed to....does anyone know if this would just be part of the re-learn process after the computer reset? Or does that then point at the TCM going bad? Thanks in advance for the help!

 

Use a digital volt ohm multimeter set to a low scale ac voltage. Connect the meter leads to the battery posts - positive lead to positive battery post etc. Start the engine and rev to 1500rpm. Not clear on the spec for these vans but the meter should not read more than around .3 vac. Various vehicles range from .2 to .5 volts. If it's out of spec either change the alternator diodes or the alternator.

These erratic gauges and shifting problems started after you installed the used alternator right? Don't even think about a new TCM.

The transmission input/output speed sensors normally produce an ac sign wave as they operate on a dc input. Introduce an ac voltage and all hell breaks loose. The speedo uses the output speed sensor as it's reference signal.