M-30 trans will not upshift to o/d

[oextrader]

My cherry 1991 M-30 (68,780 mi) will not upshift into o/d (4th gear) with the shift lever in D, and the o/d button on the shift lever engaged -- the o/d light on the dash goes out when button is engaged. The transmission just won't upshift no matter what... It just stays in 3rd gear.

This problem began just after having the battery replaced. Maybe only a coincidence.

One person told me it may be a speed sensor that failed, since the transmission normally does not shift into the o/d gear until the speed reaches about 40 mph.

The speedo still works properly, so it should not be the speedo's fault.

I realize M-30 owners are getting about as rare as "hen's teeth", and that is a terrible shame in my opinion, but maybe one of you out there knows someone with an M-30 or a 91 or 92 Nissan Maxima ( it has the same transmission) that has had the same problem.

You folks don't even want to know what a dealer service rep said -- and the cost!!!

[greg_atlanta]

I think it's a sign of transmission going into fail-safe mode because of imminent failure. 12-13 years on a transmission regardless of mileage is about as good as they get... whatever your dealer suggested is probably the right fix (replacing transmission) but you should be able to get the work done for less elsewhere.

I think (???) it's same transmission as 300Z (maybe someone else can confirm) so might be a good idea to shop around at independent shops.