240 M46 Overdrive Relay Pinout/Wiring Diagram?

[dl242gt]

I recently helped a friend wire up the broken wiring to fix o/d
in his 740T wagon. It hadn't worked in ten years. It acted funny
at first going in and out of engagement. Then after he flushed the oil a couple times it has been fine.

 

[the_hairy_baboon]

well now I can't get the relay to trigger at all. I checked 4th gear switch, shifter switch, ground continuity, supply voltage, no relay noise (not like when I tested it prior with KeyII position but engine off).

My bench setup right now can only do 6V so it's not clear if that will set it properly or if I need to get more voltage before I can test it. Anyone know the general minimum voltage / current supply needed to get the circuit to trigger? It's just running an LED so as long as the relay will flip I don't need any more current.

Also, anyone got recommendations for a variable power supply (3-20V sort of thing) with decent current capabilities? Any features to look for / avoid?

 

[the_hairy_baboon]

Got a power supply off amazon. Seems to work fine.

OD relay also works fine, even down to 8V (with good grounds). At 7V it doesn't work. In my car it's been getting ~11-12V IIRC.
I then tested adding resistance to grounds (poor connection simulation). At 8V supply and 680 Ohms to ground on 4th gear switch it stops working. However, if I put both the base ground (pin 31) and the 4th gear switch through the same resistance to ground, it stops working at ~30 Ohms at 8V.
So once I go back in vehicle it sounds like I should really confirm my connection for Pin 31 to ground, and make sure that the supply voltage relative to that ground is good. Then I check 4th gear switch to make sure its still a pretty low voltage. Record the supply voltage and resistances, recreate on bench, check if relay works. Then try putting the relay back into the vehicle.
Do any of these sensitivities sound like they're outside of spec?

 

[the_hairy_baboon]

Measured all the possibly relevant voltages and resistances, nothing stood out of the ordinary, put the relay back in and it works. Now I have a power supply I guess.

 

[the_hairy_baboon]

Well, whatever happened back in early 2023 has happened again. OD wouldn't get relay click. Tested signals in vehicle, everything looked ok. did KeyII stationary engine off, engaged 4th, switch changed like it should but OD wouldn't trigger.

Took it off the vehicle, wired it up on my desk, relay works fine. Put back on my vehicle, repeat above test, it works fine.
So..... this isn't a modern computer with weird uncleared processes - anyone know what happens that makes it need being removed and put back in again? (can't 100% say bench test was needed vs just generically unplug it....)

Cause I'm stumped as to what exactly to try to fix to make it work reliably.

 

[simgiakho]

Testing & Bypassing the Fourth Gear Switch:​

You can test or bypass the fourth gear switch by grounding the relay pin that connects to it. This effectively tells the system that you're always in fourth gear, allowing you to engage overdrive at any time (though you'll need to be careful not to engage it in lower gears). Here's how:

• The relay pin connected to the fourth gear switch typically gets grounded when in fourth gear. By identifying this pin (using a wiring diagram or pinout), you can directly ground it to bypass the switch.
• Pinouts can vary depending on the exact model year, so finding a service manual or wiring diagram for your specific vehicle will be crucial. You might find the pinout in online forums or a Volvo service manual.

If the problem persists after bypassing the switch, then it’s more likely an issue with the solenoid or wiring leading to the solenoid. https://hocvn.edu.vn/

 

[dl242gt]

Should only be done for testing purposes. it's too easy to forget and be in overdrive in first or even worse go into reverse by mistake and that can damage the unit.

 

[diogov20vt]

I have the same problem, when cold need to jiggle the gear shifter in 4, to stay engaged, when its fully warmed up, engine and transmission, just works fine, it might be the gear switch with bad ground, but for some reson when warm works fine, its a d24 with m46

 

[the_hairy_baboon]

and.... OD not working again but for probably a different reason. Button turns on/off the light on dash, so we know the 4th gear switch is working BUT OD won't engage, even with the press clutch and release system jarring action (that used to be decently reliable).

Reading through notes here and some other O/D docs I have, I should first make sure the full electrical path is good - sufficient voltage to the relay, relay clicks properly (think it would have to for the dash light to show up) and that there is appropriate resistance down the path to the solenoid itself.