'93 240 with automatic trans.

Arrow shaped overdrive off light on dashboard is lit all the time when engine is running. Where do I start troubleshooting?

 

Could be either the OD solenoid on the transmission or the relay that drives it. I would check the relay first. To access the relay, you need to pull out the glove box and it should be just to the left (under the center dash vents). Typically the solder joints on the relay go bad and can be re-soldered if you are handy. Otherwise you can just replace with one from a junkyard or a new one if you have more money. If you search the forums (or perhaps BrickBoard), there are instructions on how to test the relay.

If the problem is not in the relay than it is most likely the solenoid or the wire that runs to the solenoid. This wire can become frayed and short out. You need to crawl under the car to check it. I believe it is the only wire that runs to the transmission.

If the wire is ok, then the last thing to check is the solenoid on the transmission that deactivates the overdrive. IPD sells a bypass kit that replaces the solenoid and basically makes it a 4 speed trans all the time. This is a cheaper route than replacing the solenoid.

Good luck.

 

Before all that, is your o/d actually disengaged or is it just the light? Count the shifts up and listen for abnormally high revs around 85 km/h. The instructions above apply if you actually have a permanently disengaged O/D. It could just be the indicator light stuck on.

 

I used the bypass kit ($40) from IPD. The only disadvantage was that I was unable to get it flush. So it leaked transmission fluid. I was so mad at having to fill up with transmission fluid all of the time, I decided to by the actual part ($79) from EEuro Parts. Unfortunately, the wiring harness was destroyed by the drive shaft, so I had to solder the wiring. Now it works like a charm.

 

ALWAYS TEST FIRST DON'T JUST PULL AND REPLACE GOOD PARTS....Check in this order always...1. Check Fuse with a test light if fuse is good and has a solid connection 2.Put right ear up next to left of glove box while key is on but car not running push the overdrive button and see if you hear a "click" you know you have power to the relay. If you hear a real faint click or no click most likely a relay...but don't just pull and replace you need to know 100% 3. you really need 2 people for this and must have car on(not running) but key position all the way to the right and while someone holds a test light on the solenoid and someone pushes OD button make sure you have power to the solenoid. If no power to solenoid most likely a bad relay or severed wiring somewhere. 4. check wiring first it sometimes gets melted by the exhaust. 5. If all wiring is good 6. Test switch with test light push button in light should go on push in again light should go off. If it does not and light only stays on you have a bad OD switch. If switch is good and no power to solenoid then 6.replace relay but 7. If you have power to solenoid then you have a bad solenoid. I am not a believer in just pulling and replacing good parts thats not how you diagnose something. Doctors just dont say hey, maybe it's a bad heart let's replcae it and find out...same with good mechanics...Testing is how we always proceed when something is not working. You will never be a great mechanic or diagnostician if you only pull and replace....and in the long run it will cost you a lot of time wasted, frustration and $$!!! If nothing else and you want to try to diagnose problems on your own car and not pay a professional, go buy yourself a test light a multimeter and an IR temp gun...as you get into it you may want to get a fuel pressure gauge with these 4 tools the Volvo Forum and a Hemmings manual you will save A LOT of time and $$ and frustration!! Sorry to be so passionate but I was you 5 years ago... I was the king of pull and replace got me nowhere fast...Hope this helps