Fluctuating Tachometer

[jerseyguy123]

While driving my 2010 Caddy (6 speed auto V-6 at 70 the tach usually reads about 2300 RPM. Now when I
get to 70 the tach goes to over 3,000 and stays there. I can hear the tranny shifting and then the tach
returns to its norm. The engine does not increase revving. I hope I gave enough info, and thanks for
your help.

 

[Pelican]

Originally Posted by jerseyguy123
While driving my 2010 Caddy (6 speed auto V-6 at 70 the tach usually reads about 2300 RPM. Now when I
get to 70 the tach goes to over 3,000 and stays there. I can hear the tranny shifting and then the tach
returns to its norm. The engine does not increase revving. I hope I gave enough info, and thanks for
your help.


Sounds like the tranny's misbehaving

 

[silveravant]

Sounds like it could be a problem with the torque converter lock-up clutch.

 

[spk2000]

Transmission slipping

 

[mattd]

Converter may not be going into lockup. I would think that if the pcm commanded lockup and did not see it it should throw a code. You'll need a scanner to look at desired slip vs actual.

 

[Number_35]

OP, I'm not sure whether you're saying that the tach is reading higher than it should, or whether you figure the transmission is shifting and/or locking up later that it used to.

If the latter, does the delayed shifting/TC lock-up coincide with cold weather? The Jatco 4-speed automatic in our old '97 Mazda MPV did not shift into O/D (4th) gear until the ATF temperature hit, IIRC, around 50 C. I'd see the two drops in RPMs, one when the tranny went into 4th and the other when the TC locked up.

 

[mk378]

Hook up an OBD scanner and see if the PCM rpm numbers agree with the dash tach.

 

[HowAboutThis]

If it's electronics related in the transmission, try pulling a battery cable or fuse hoping for a clearing/reset of the transmission computer. Cheap, easy, and 5% chance it'll work...