weird auto box fault - any ideas?

Hi All,

Posting this question on behalf of my farther - he has 1997 4.6 p38 - on Thursday he had a puncture where a metal spike went in the inside side wall of the n/s rear tyre and started clattering about - wheel and tyre changed and checked for any damage that could have been caused by the spike hitting the underside of the car - no damage found so he continued on his journey. However if the vehicle goes over 2000rpm while in 'D' all drive will be lost unless you lift off the throttle and allow the revs to drop below 2000rpm and drive returns. If you put the box in 3rd it will maintain drive at all engine speeds. Is the puncture and this fault related or just co-incidental? I suspect its one of the auto box clutches that has failed as we've checked fluid level and color and all is fine and there are no error messages coming up on the dash. Anyone got any ideas what the exact fault maybe?

Cheers
Andy

Sounds more mechanical than anything else. A pure guess to get you started would be the sudden reduction in wheel size on the tyre being punctured has upset the box somehow because of the sudden deflation and the knock on effect of that wheel having to go faster to keep up. (Smaller circumference = greater spin speed). Could be entirely coincidental to a pre-existing problem that was about to go in any case as plenty cars get punctures. The other thing is he could have knocked out a sensor somewhere which is putting the car in get you home mode hence the lower revs.

Has the car got traction control, could the wheel speed sensor be damaged and giving false readings, Thats all I can think of but it would affect abs too I would have thought?

Hi guys thanks for the replies - yes the car has traction control but i to thought that if a speed sensor was damaged the abs light would stay on and there would probably be an error message displayed on the dash to. If drive was lost above 2000rpm in all gears i could pretty much guarantee one of the gearbox clutches - just seems strange that its only in 'D'.

If you have any more thoughts let me know.
Cheers
Andy

I know these gearboxes are very voltage critical, try checking the battery connections and the charging, Just another idea..?