Unexpected Downshifts

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Dec 18, 2003 | 12:30 PM

mdbell

Thread Starter

New User

Joined: Apr 2002

Posts: 11

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From: Houston

Unexpected Downshifts

I've got a 97 F-150 4.6L with an auto tranny that periodically downshifts from OD to 3rd at highway speeds at constant throttle. It doesn't happen very often - sometimes it can go as long as a couple of weeks acting normally. The erratic downshifting definitely seems to happen more often in hot weather. In fact, the tranny hasn't downshifted at all since the outside temp during my morning and evening work drives seems to have dropped below 70F in Houston for the winter.

Other than the occasional bizzare shift, the transmission seems to be working perfectly with no clunking and very smooth shifts. Also, the throttle position sensor and the trans fluid/filter (Mobil-1 ATF) have been replaced recently with no improvement.

I'm starting to think that maybe some electronic gizmo on the circuit board that sits down in the tranny oil has glitched out or just become heat sensitive. I assume that there no way for normal folks to trouble shoot the circuit board components- so can the entire board be replaced easily and cheaply? Is there an aftermarket alternative?

Thanks for any help.

Dec 18, 2003 | 01:47 PM

f150-az

Senior User

Joined: Apr 2003

Posts: 262

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From: Tucson

ya, best bet is to take it in. Auto trannys are so complicated that you'll never figure something like that out on your own.

Dec 18, 2003 | 05:53 PM

LxMan1

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Joined: Dec 2001

Posts: 22,436

Likes: 17

From: Louisville,Ky.

I had on odd shifting problem with my Windstar once. A buddy of mine had a Sable that would downshift into first @ 55mph for no reason.
On both of them, it turned out to be the shifter position switch on the tranny where the linkage goes into it. It tells the computer what gear the tranny is in.
It may not be your problem, but I just thought that I would throw this info out there, just in case.
Has your OD light ever started flashing?
Mine never did when my van was acting stupid.
Jimmy