Loss of speed uphill on cruise control
tandc99
07-19-2006, 08:21 PM
I have a 1999 T&C with 117000 miles. Van runs fine except when I am on cruise control and going up on any incline. When heading up a slight slope at freeway speeds, on cruise control, vehicle looses speed gradually and the Torque Converter does not unlock to downshift so engine can maintain the speed and transmission stays locked in high gear, till I hit about 45 MPH. Then it will maintain 45 MPH till over the hill then gain speed to cruise set speed and and upshift to lock torque converter. It does not matter whether I am going 50 or 75 MPH, the engine does not downshift to maintain speed always on inclines. It is amazing how I loose speed from 75 MPH to 45 MPH while locked on high gear in cruise control without any response from the transmission. However, when going downhill, increase of speed over 3 MPH downshifts transmission to regulate speed so well.
What sensors are not working?
If not using cruise control, vehicle downshifts uphill so well so I doubt it is the transmission.
Thank you.
What sensors are not working?
If not using cruise control, vehicle downshifts uphill so well so I doubt it is the transmission.
Thank you.
neon_rt
07-20-2006, 10:37 AM
I have a '00 GC 3.8l that does that once in a while.
I suspect the trans fluid temp sensor (if this model even has one).
On some models I have noticed that in the manual there is a mention of said sensor. And that if fluid temp is too high the TC will remain in the locked state to avoid overheating the fluid. It's a possibilty.
My other '00 GC 3.3l started locking the TC in all gears a couple of years ago on a road trip through the mountains. It was 100' and the A/C was running full blast. Every time the trans shifted down the TC would lock a couple of seconds later.
I suspect the trans fluid temp sensor (if this model even has one).
On some models I have noticed that in the manual there is a mention of said sensor. And that if fluid temp is too high the TC will remain in the locked state to avoid overheating the fluid. It's a possibilty.
My other '00 GC 3.3l started locking the TC in all gears a couple of years ago on a road trip through the mountains. It was 100' and the A/C was running full blast. Every time the trans shifted down the TC would lock a couple of seconds later.
tandc99
07-21-2006, 06:13 PM
I have a '00 GC 3.8l that does that once in a while.
I suspect the trans fluid temp sensor (if this model even has one).
On some models I have noticed that in the manual there is a mention of said sensor. And that if fluid temp is too high the TC will remain in the locked state to avoid overheating the fluid. It's a possibilty.
My other '00 GC 3.3l started locking the TC in all gears a couple of years ago on a road trip through the mountains. It was 100' and the A/C was running full blast. Every time the trans shifted down the TC would lock a couple of seconds later.
This lockup of TC happens even when the transmission fluid is cold right after starting a trip. The other thing however is if the incline/hill is abrupt i.e. sharp hill coming after a dip, the downshifting is instantenous and vehicle keeps set speed. However, on gradual inclines it is when it will keep TC locked till I hit 45 mph.
I suspect the trans fluid temp sensor (if this model even has one).
On some models I have noticed that in the manual there is a mention of said sensor. And that if fluid temp is too high the TC will remain in the locked state to avoid overheating the fluid. It's a possibilty.
My other '00 GC 3.3l started locking the TC in all gears a couple of years ago on a road trip through the mountains. It was 100' and the A/C was running full blast. Every time the trans shifted down the TC would lock a couple of seconds later.
This lockup of TC happens even when the transmission fluid is cold right after starting a trip. The other thing however is if the incline/hill is abrupt i.e. sharp hill coming after a dip, the downshifting is instantenous and vehicle keeps set speed. However, on gradual inclines it is when it will keep TC locked till I hit 45 mph.
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