i lose a gear when the check engine light comes on

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my 1984 olds 98 has had some trouble when im on da highway. sometimes the check engine light comes on and it seems as though i lose a gear and my rpms increase. sometimes it will shut off and will upshift but sometimes it doesnt. it only does it in overdrive. the tranny is a thm200-4r. i know this tranny is not very good for the weight of the car because i have read about a lot of people that have had trouble with them. any help is appreciated.

posted by  84olds98

why do you drive overdrive on the highway, just wondering

posted by  Import-tuner

Because that's what overdrive's for...... Decreases ratio to about 0.75:1 to increase economy.

posted by  88GrandPrixSE

i know what overdrive is and what it does, i asked him why does he drive in overdrive if thats what causes his problems.

posted by  Import-tuner

check the codes. A GM 4 speed THM has inputs to the ECM via the various relays in the tranny identifying which gear the car is in.

posted by  tbaxleyjr

well right now i am getting 10 mpg if im lucky so i need all the help i can get. i am going to check for loose wiring. someone told me that it may be the torque converter coming unlocked so i gotta go through all the sensors and stuff. next time im out ill see how much of a gear reduction i lose, like if its a whole gears worth or not.

posted by  84olds98

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