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Old 01-29-2018, 01:12 PM   #1
Magnanimous
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Default m46 overdrive intermittently not working/letting go

A few weeks ago the overdrive switched off on its own while I was on the highway. I was able to turn it back on, but it switched back off a few moments later. Since then the overdrive hasn't been working right. Sometimes it works fine and I can turn it off and on as needed without it letting go on its own, but most of the time it either doesn't turn on at all, or it lets go shortly after I manage to turn it on.

When it doesn't turn on, I can't feel the switch "click," and it seems to work more reliably during the day or when its warm(er) out, though I live in Florida, so it's always pretty warm.

The overdrive wasn't working at all when I first got the car ~2 years ago, but it was just a disconnected switch, and I was able to re-solder that pretty easily.

I checked the transmission fluid levels, and they were fine. Where should I go next in terms of troubleshooting?
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Old 01-29-2018, 01:37 PM   #2
ZVOLV
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Does the light go on and off while this happens? If so, I would suspect the relay.

Lift the car and inspect for bad wiring to the solenoid.
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Old 01-29-2018, 01:50 PM   #3
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Sounds like a relay issue. Open it up and repair any cracked solder connections.

https://www.volvoclub.org.uk/faq/Ele...olderingRelays
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Old 01-29-2018, 03:30 PM   #4
John242Ti
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Could be relay, or it could be the 4th gear switch on the top cover of the transmission that's wearing out. If it engages reliably if you push the shifter toward the rear passenger corner of the car when it's in 4th gear, then it's that. If it doesn't help, then time to reflow solder in the relay and to check the red wire that goes down through the hole in the tunnel. That said, I've had issues with the OD switch itself going bad. Had one in my old '83 245 that would engage the overdrive just fine, but didn't like to disengage it. At the same time, the 4th gear switch had blown, so it was bypassed until I got a new one. Bad idea. Pulled into a parking lot, realized I was in the wrong spot, so engaged reverse. Overdrive was still engaged. A couple thousand miles later, was driving along and engaged the overdrive. Blew it.

-J
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Old 01-29-2018, 05:48 PM   #5
Magnanimous
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Quote:
Originally Posted by ZVOLV View Post
Does the light go on and off while this happens? If so, I would suspect the relay.

Lift the car and inspect for bad wiring to the solenoid.
The light comes on when the overdrive actually engages, but doesn't come on when it's not working.
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Old 01-29-2018, 06:06 PM   #6
planetman
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That's a classic relay or wiring issue and because the relays are known to fail, I would suspect the relay 1st.
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Old 01-29-2018, 06:28 PM   #7
Magnanimous
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Is this the location of the OD relay for manual or auto cars? Or both? the site doesn't say...

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Old 01-29-2018, 07:55 PM   #8
John242Ti
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Both Aw and M46 have it there. Will be a red relay.

-J
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Old 01-31-2018, 03:51 PM   #9
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Mine is blue, 85 745 M46. Yes it did need resoldering, at the small 90deg bends next to the plug blades platform. Required a strong light and hefty magnifying glass to see the broken (cold) solder joints.

Symptoms: Inconsistent OD engagement. Sometimes I could get it to engage by (while the ashtray and relay/fuse cover was off) "massaging" the relay while attempting to engage OD. This is what pointed me to the relay as being faulty.
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Old 02-01-2018, 09:14 AM   #10
oifish
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Check the wiring under the car as well. A part of mine wore away and would short against the frame, causing weird intermittent issues.
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Old 02-01-2018, 05:48 PM   #11
Magnanimous
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For resoldering, did you guys apply new solder or just melt and re-flow the original solder?
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Old 02-02-2018, 01:17 PM   #12
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New solder, minimally applied. Requires a steady hand, good light, magnifying glass (helps to have the work and magnifying glass clamped in place) and a clean tinned fine tip on the iron. I used a very fine gauge electronic solder.

Soldering guide:
https://www.volvoclub.org.uk/faq/Ima...gTechnique.gif
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Old 02-03-2018, 11:12 AM   #13
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Had the same issue, got new relay and fixed the problem. Did the fuel pump relay at the same time as they were together behind the glove box.
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