I have a 1991 240sx with Automatic Overdrive Transmission. 165K miles.
When the transmission is cold, I am getting hard up-shifts from 1st to 2nd gear. The car has been doing this since I bought it, about 2 or 3 years now.
In the summer, when temps are in the 80's and 90's, not much of a problem and it goes away quickly. On cold winter days, there is a sharper shock in the change between 1st and 2nd, and it takes longer for the problem to go away. In general, the colder the day, the harder the shift. Otherwise, no other problems with the transmission.
I'm thinking a fluid terperature sensor inside the transmission.
Little hesitant to bring it somewhere without knowing what I am up against. Any advice is greatly appreciated.
Raven
Hard Up-Shift from 1st to 2nd Gear when Automatic Transmision is Cold
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Haven't read the FSM obviously. There is a temperature sensor in AT to measue ATF as the viscosity changes with temperature.This signals the tcu to change the duty cycle of the pressure control valve [solenoid]. The pressure variation attempts to safely allow shifts for drivers who insist upon driving a cold car or in the event of really cold external temperatures [below zero].
None of the systems are really designed [assuming max life is desired] to be driven until all the fluids reach operating temperature [10-15 minutes in cold weather].
4th gear won't engage until the ATF reach 100-110F.
None of the systems are really designed [assuming max life is desired] to be driven until all the fluids reach operating temperature [10-15 minutes in cold weather].
4th gear won't engage until the ATF reach 100-110F.
Q45Tech, thanks for your reply.
I read the 1991 Service Manual but not much help (don't know if this is the factory manual). Regarding the tempurature sensor, I only found two references (AT-7 and AT-81). Overall, your explanation was much more valuable to me.
My follow-up question is whether I have a real problem or perhaps this is something this transmission is designed to do. When I talked about hard shifting in cold weather, I am talking about a slightly harder shift at start-up in mild weather, 70 degress or so, harder shifting at 50 degrees and below. It rarely reaches 0 degrees where I live.
Your thoughts are appreciated.
Regards,Raven
I read the 1991 Service Manual but not much help (don't know if this is the factory manual). Regarding the tempurature sensor, I only found two references (AT-7 and AT-81). Overall, your explanation was much more valuable to me.
My follow-up question is whether I have a real problem or perhaps this is something this transmission is designed to do. When I talked about hard shifting in cold weather, I am talking about a slightly harder shift at start-up in mild weather, 70 degress or so, harder shifting at 50 degrees and below. It rarely reaches 0 degrees where I live.
Your thoughts are appreciated.
Regards,Raven
It is normal for a/t to shift firmer in cold weather do to fluid being thicker when cold. You tend to notice it because the fuel is increased during cold startup and the rpm range is higher and when it shifts it is firmer. The temp sensor helps to keep the trans from going into od before the trans fluid is up to temp. This all aids in quicker cat. warm up when cold.