Hi there Volvoland.
I hope you can help. I've got a 940 diesel with a manual (stick shift) gearbox. The overdrive has an intermitent fault. When I push the switch on the top of the gearlever to select overdrive 5th it does not always make the shift. Sometimes it will drop in on it's own a couple of minutes later. Sometimes it won't go in at all. Sometimes it will down shift to 4th with no prompting from me. Sometimes it will perform flawlessly for 300 miles. So, is it the switch, the relay, the solenoid? Any ideas?
Thanks, Clive.

 

Could be any of those: you have to eliminate them one by one. Check the switch, change the relay, go from there...

 

Thanks Lev. I did wonder whether that may be the case. I was hopeing that there would be an easy answer. There never is. Thanks again.

 

what year and country is this (diesel 940s were never sold in the US as far as I know)? I can dig up the greenbook and describe the OD circuitry, if that would help. from here, sounds like a flakey relay to me, but hard to say without a bunch of testing.

 

My car drops out of overdrive more in the cold. I still haven't locked it down, but wiring and solenoid I think have been looked at. It's on my to do list when I tear my car down when after I build a garage. The wires in the actual shift lever are known to chaff. I just fixed a whole harness for a 240 M46 conversion. There were a few chunks that needed replacing.

 

Thanks for you help Pierce & Titan Joe.
My 940 is a 1994 model right hand drive built for the UK where it still lives. It's got 218000 miles on the clock and has had 6 previous owners. I've had it since 2010.
Although I'm not a mechanic I can tackle small jobs so any help would be appreciated.
The wiring in the gear stick chaffing is a new one on me. It looks like I'm going to have to start with the cheapest component and work my way up to the solenoid.

 

ok, its almost 2am friday night, and I've had a few too many whiskeys and ales. muahahaha.

(a double shot of Jamesons over a tall glass of ice, with a jolt of fresh lime juice+syrup sour mix, and a splash of soda, makes a very good first drink when you get home late after a long day).

I'll dig up the wiring diagram on that version tomorrow, its probably on this DVD, and try to describe the circuitry, wire colors, connectors, and maybe my seat-of-the-pants engineer's idea as to why it might go wrong.

I do suspect its either the control button wiring, or the solenoid, but some tests with a digital volt meter, and/or a test light, will likely help narrow it down.

whats your level of expertise in electrical troubleshooting? do you understand the basics of electricity, ohms law, current flow, how to use a volt and ammeter, and so forth?

 

 

lets see, parts...

1/1 - battery (duh)
2/8 - overdrive relay
3/1 - ignition lock
3/42-1 - switch on transmission
3/43 - switch in gear lever
5/1 - combined instrument panel
8/1 - overdrive operating solenoid
10/80 - overdrive indicator light
15/1 - positive terminal
31/10 - ground at right A post
31/28 - ground at overdrive solenoid
31/31 - ground rail in fuse/relay panel

c2 - 53 pin connector - instrument panel harness - door sill harness
c113 -
c117 - 2 pin connector - left wheel housing - engine harness
c166 - connector at electrical distribution unit, 8 pin

 

Mine had suspiciously similar symptoms. Turned out it was cold solder joints in the OD relay (# 2/8 in the diagram above).

Opening the relay can and inspecting the circuitry with a magnifying glass and strong light showed multiple failed solder joints (all in a row) on the row of right-angle connector stubs at the bottom edge of the mini circuit board inside.

Successfully fixed with a sharp point low-wattage soldering iron and some fine gauge electrical solder.

 

Sorry I've not got back to you sooner but it has been one hell of a week culminating in my poor 940 cooking it's engine. It is uneconomical to repair as I'd have to replace the engine. It happpened when the radiator blew on the motorway and the engine overheated before I could pull onto the hard shoulder. We were hoping that the engine would be ok so replaced the radiator. When my mechanic put the new rad in and started it up he had exhaust fumes coming out of the water header tank. So, my little problem with the overdrive as been eclipsed by the car coming to the end of it's life. Very sad. So thank you for all your help but I'm afraid it has been for nought. I would love to have another Volvo and if I do I'll come back and rejoin you all. Thanks again, Clive.