Just got my 240 back on the road. Turns out it needed a new fuel control unit. But now I'm having another problem. The overdrive refuses to work properly and seems to have a mind of its own. It's an automatic and when you start the car sometimes the overdrive is engaged and sometimes it isn't.

When it isn't, pushing the O/D button only rarely works. Most times you push it, nothing happens (not even a click from the switch), then sometime later the overdrive comes on. Worse is that it will disengage overdrive on its own for no reason if you do manage to get it back on.

When it is engaged when you start the car, the O/D button works perfectly turning it off (O/D switch clicks when it does this). But it will rarely come back on by pressing the button. And once again you don't have to push the button for it to turn off. It'll do it by itself.

I've already pulled the O/D switch off of the car and tested the continuity. It is open unless you have the button pressed down all the way and doesn't stay closed. Don't know if that's normal because I can't find electrical specs for the switch anywhere.

 

The switch seldom fails. First suspect is the od relay. Second suspect would be the wiring under the car leading from the od solenoid forward into the car. Over the years, exposed to road grime and debris, engine oil and transmission fluid, the wire insulation can break down and start shorting on the chassis.

 

What should I see from pin to pin on the relay when I test its resistance? I'll go ahead and do a visual inspection of the wires underneath assuming I can reach them by lifting the front of the car with a floor jack.

 

FWIW, I had my mech. mod the Tranny with the IPDUSA overdrive mod plate and have not had any other problems.

 

had a similar problem. took out the relay popped off the case and saw one of the solders was bad. resoldered and worked fine after. worth a try. takes 5 mins

 

That's what I did. $40 and no more switches or relays or solenoids to go bad. It's working great.

 

I just bought a 1990 240 DL and sometimes the OD worked most of the time it didn't... So I read this forum did what this guy said about checking the solder on the OD solenoid and sure enough one connection was broken... Soldered it again and it worked just fine.... Thanks alot only took 5 min and I'm sure it saved me lots of money....

 

Hey i am new and i know this is an older post but i was curious i removed my OverDrive relay to try and fix it and my brother turned my car on without knowing and the the light stayed off and would not turn on. is there a down side to driving without it attached?

 

No damage will be caused by driving without the relay installed. Does the light stay on after you re-installed it?

 

it does not stay on i just lose control over it. the light will come on at random times and i can not shut it off, normally i would think its doing it because it needs to but it would switch on the highway so im going about 60 in 3rd.

 

a common problem with the electric OD is the wiring to the pushbutton on the shifter. very hard to fix this.

you didn't say what year/model car you have.