Cruise Control Problem?

I occasionally get the impression the cruise control on my 2000 Chrysler
Concorde LXi isn't operating properly. When set at about 60 mph, it
occasionally feels like it down shifts. The RPMs rise to about 2900 to 3000
and I feel a shift in the transmission. The hill involved is from a series
of "washboard type" that rise rather sharply then decline. The distance of
the hills on any given rise or decline is perhaps a half mile at most;
usually one quarter of a mile or less. It doesn't occur often. When it does
though, I've begun simply shutting off the cruise control. On mostly flat
stretches, everything is fine. Is this normal?

 

When climbing a grade the speed control tries to maintain the set speed by
increasing the throttle opening, while inability/delaying downshifts..

If opening the throttle alone cannot maintain the set speed and the vehicle
speed drops more than three mph below the set speed, the transmission will
downshift to third gear. If the vehicle continues to lose speed, by more
than 6 mph, the transmission will downshift again maintain the set speed.
After the vehicle encounters a less-steep grade, or has crested the grade
(reduced the load on the powertrain) and can maintain the set speed at a
reduced throttle position, the transmission will upshift, as appropriate,
until the set speed can be maintained in Overdrive.



Glenn Beasley

Chrysler Tech

 

I've never noticed anything "out of the ordinary" while going up hills. This
occurs only going downhill. Isn't the brake system supposed to come into
play when doing downhill to reduce the speed. If set at 60 and I start
picking up speed, I occasionally feel it shift and the RPMs run up to around
3000. That happens rarely... but it does happen. I thought perhaps the
mechanism that's supposed to kick in the brakes wasn't doin' its job and the
transmission took over.

 

Transmission control software includes an automatic speed control overspeed
reduction feature. This maintains vehicle speed at the selected set point
when descending a grade.
The Transmission Control Module first senses that the speed control is set.
If the set speed is exceeded by more than 4 mph and the throttle is closed,
the TCM causes the transaxle to downshift to 3 rd gear. After downshifting,
the automatic speed control resumes normal operation. To ensure that an
upshiftis appropriate after the set speed is reached, the TCM waits until
the speed control system opens the throttle at least 6 degrees before
upshifting to overdrive again.

If the driver applies the brakes, canceling automatic speed control
operation with the transaxle still in 3rdgear, the TCM maintains this gear
until the driver opens the throttle at least 6 degrees to avoid an
inappropriate upshift. The upshift is also delayed for 2.5 seconds after
reaching the 6 degrees throttle opening in anticipation that the driver
might open the throttle enough to require 3rd gear. This will avoid
unnecessary and disturbing transmission cycling. If the automatic speed
control Resum feature is used after braking, the upshift is delayed until
the set speed is achieved to reduce cycling and provide better response

 

Thanks. From your description, it appears everything is operating as
designed. Maybe I've simply not noticed the downshift in the past. I
appreciate the explanation.