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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?

Reply to
John Gregory
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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

Reply to
maxpower

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.

Reply to
John Gregory

appropriate,

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

Reply to
maxpower

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.

Reply to
John Gregory

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