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1990 Volvo 240 Sedan Overdrive Switch

I have a 1990 Volvo 240 4 cyl Automatic Trans. On the Shift lever is a Overdrive Switch which allows you to shift in and out of Overdrive. The indicator is a Yellow Arrow on the dashboard.If you press it the light should go on or off depending whether you want to be in Overdrive or not. My car’s switch has a mind of its’ own. It will be on or off at the startup and will sometime respond or not respond to my pressing of the switch. Sometimes it will engage itself without my pressing the switch at all. I could be driving on the freeway and it will shift into a lower gear. Sometimes multiple pressing of the button will turn it off sometimes not. It does not seem to have any rhythmn as to how it responds. I have replaced the switch to no avail. No one can figure what to do. Can you help?

I have an old Toyota with the same goofy feature. The switch actually disables or enables the automatic overdrive, it doesn’t activate it. It’s intended to allow the driver to restrict the auto-transmission to the bottom three or four gears if disengaged, or if engaged to allow the transmission to automatically shift into the highest (overdrive) gear to reduce engine rpm, saving fuel and engine wear.
Set the switch so that the overdrive engages automatically at the appropriate speed and leave it that way. If you find that at times the car does not downshift while you are climbing a steep hill at highway speeds, and you start losing speed as a result, that is when you would want to use the switch to disengage the overdrive gear. Then you would use it to allow use of the gear again on more normal terrain.

Thanks for the reply, but my problem is different. I have a button on my shift level which I press to engage or disengage the overdrive. My switch does not repond to pressing the switch. It will engage or disengage at will and I cannot reverse the action by pressing the switch. It has a mind of its’ own.

Check on Brickboard, a discussion board devoted solely to Volvos. My 1983 was a manual transmission and perhaps not the same setup as yours, but it had the overdrive relay mounted into the transmission housing. I had to replace to relay to cure the fact that the overdrive would not engage. The switch on the shifter was a separate issue. The folks on Brickboard will have more detailed knowledge.