My 2003 Caravan stopped shifting and logged codes related to input speed sensor and gearing problems.

I replaced both input and output sensors and things were fine. For one day.

Now the codes are back.

The wiring on the input sensor was scary tight. Just way too short, pulled tight like a guitar string at a 90 degree angle to the connector. I was afraid to unplug it, but made some slack by moving the harness around.

This post and this auction lead me to think I should focus my attention on the input speed sensor portion of the wiring harness.

Thoughts?

At this point I'm tempted to just lop off the connector and solder in a new pigtail.

If I knew where the pigtail wires went, I suppose I could ohm them out...

Thanks!

 

I'm not even close to an expert or even that experienced, but there are the two speed sensors, ground wire by starter that I think goes up to the engine ground screw on the firewall, some torque converter sensor up on the bell housing somewhere that looks like the speed sensors do, and the solenoid pack connector. I think that's all external wiring on 3rd and 4th gen caravans.

There might possible be more, I think I seen another speed sensor looking plug botton-right of the solenoid pack on some, and maybe temperature sensors somewhere too..

It's cheap to get a generic trans ground wire and dialectric grease from a local parts house and change that out without removing anything. I've actually seen a significant amount of reports of this causing sporadic trans issues.. It's good preventive maintenance.. At first I though the TCM and it's wiring were big issues with caravans, but later I find messing with it usually is just covering up real problems by resetting and flashing..

 

Are you suggesting I should rip the whole wiring harness out and fiddle with it on the workbench?

...or that I might ohm things out in place, or what?

Interesting. So a bad ground might be my issue? I'll look for the ground wire by the starter that you mentioned.

"this" - you mean that bad grounds cause problems and keeping an eye on the ground cable is good policy?

I appreciate the tip, I'll see if I can find the ground cable, check its condition. I'll also see if I can detect any voltage between the trans housing and the negative terminal of the battery.

 

Ground wire isn't a frequent problem. Just check it when you have these issues because it could be damaged or corroded; a new one with grease will probably not need checked till the vehicle dies from cancer or not being worth rebuilds.. The highest frequency problem is the solenoid pack, next are probably the speed sensors. There are also ECM, TCM, BCM manufacturer updates, but good luck finding someone to flash them, telling if you need them, or even if an update exist(someone going to make money doing it for you might not be honest)..

One more problem is an unidentified piece inside the tranny that is supposedly the cause of a lot of dead mopar FWD auto trans. I still can't find the source website I read, but once a mechanical engineer tore down a lot of these mopar FWD trans and found a single piece to be the cause of almost all none-external failures..

Stuff up around the TCM(besides updates), main wiring loop and other main stuff that mostly stays still, isn't as frequently the real issue as the immediate internet search will lead you to believe.. Even most of the stuff that is expensive to replace inside the tranny isn't(it's mostly stamped alloyed steel), except that one piece.

EDIT: Also, I think the ABS system can effect the trans.. But when it has issues it's almost always the need of a break job, or one of the four ABS speeds sensors is faulty.. You'd likely see an ABS light on the dash somewhere if it was this though..

 

I found the problem.

I mentioned before that the wiring on the input speed sensor was scary tight...

Well, it appears to have been routed wrong, probably from the factory.

Just a couple of inches to the right of the input speed sensor are two very heavy branches of wiring harness. One branch wraps over the top of the transmission, toward the firewall. The other branch goes straight up (maybe to PCM? I don't remember).

The wires for the input speed sensor were run below both of these branches, trapped between the firewall-bound branch and the transmission. That's why it was so tight.

The wires probably should have been routed through the middle of the Y shape formed by these branches of wiring harness.

One of the wires broke right at the edge of the connector where it plugs into the input speed sensor. I probably should have noticed the damage when I replaced the sensor.

I chopped off the bad plug end, wired in a repair plug from ebay, and everything's happy now.