Picked up a high mileage 2000 4.7 Dakota CC with an auto trans in it a few months back. PO forgot to mention the accident it was in, or the head gasket leak, but I can live with those. The scary issue I've got is that the transmission will violently downshift from 4th to 3rd, for no reason, about every fifteen minutes on the highway. Happens uphill, downhill, no hill, 50 mph or 80, BANG, like a neutral drop, and it'll hold third gear for about 5 seconds, regardless of throttle position, and then upshift nice and smooth. Fluid is red and not stinky, all other shifts are completely normal. Anyone have any ideas? This is my first auto trans problem in almost a decade, and my first Chrysler product ever. I don't even know where to start. Another forum recommended I check a pressure sensor near the cat, which I did and it seems to be in order.

 

Drop the pan and change the filter/s. Be sure to put in ATF+4

 

Welcome to the forum DoubleJ.

Any codes? You don't need a scanner. With the truck not running turn the key to ON (don't start it), then back to OFF, turn it ON again, then OFF, finally leave it in ON. Any codes will display in the odometer. It'll show P DONE when finished.

I'm thinking TPS.

 

Thanks for the welcome, glad to be here. No CEL, and I did the key trick just now and it displayed my mileage, then straight to P DONE. That's a neat trick.

 

So 00, you're thinking maybe my TPS is reporting to the ECU that I've asked for a downshift when I haven't? I can dig it, except for the violence of the downshifts. When I do ask for one with my foot, it's smooth and normal, these random ones are like hitting a massive pothole, they literally set your heart to pumping hard they're so sudden and surprising. TPS still a possibility?

 

That's what I was thinking, yes. But it shouldn't be that violent.

A new TPS is cheap, so is the fluid/filter(S) change, yes both of them and use MOPAR filters! Lots of aftermarkets cause problems.

After that I'd be looking at a transmission shop.

 

I'm almost thinking it's an internal issue with fluid/pressure seeping past a seal. The 545RFE box is very complex inside. Could spend days lookign through the FSM for ideas.

 

Probably wouldn't hurt to do a trans service on it anyway, so I'll get to that once I get done with 1100 other things I've got going on between the two vehicles.

As for the violence of the downshift, if I was taking guesses based on my limited knowledge of auto trannies, I'd say that some doodad is malfunctioning in the transmission or a computer somewhere, and calling for the trans to shift 4-3 when it's not needed. Other doodads that are necessary for smooth shifting (solenoids, valves, etc) aren't being informed of the shift request, since it's make-believe, and aren't actuating. The transmission then goes "what the *&^%% am I doing in 3rd gear?" and actuates all of the appropriate doodads required for a proper, and smooth, 3-4 shift.

That make any sense?

As for a trans shop, I gave 3K for the truck, probably be better off replacing it with a junkyard trans if it breaks.

 

Now the truck has completely quit doing it and is acting totally normal. What does that mean?

 

I wouldn't wait. The tranny would be a costly failure. Again, drop the pan and change the filters. Sounds like you have shifting blockage affecting pressure. I used to have an old Infiniti Q45 that would do that every time the screen mesh clogged. Also, the fluid might be red, but you don't know if it's ATF+4.