Ok, I got my hands back on the car today.

The 'bucket' was free of noticeable spills and debris, except for light dust and an old dime. No rust, slime, or goo.

I gently blew out the area with a compressor and captured as much as possible with a vacuum.

The park lock solenoid gets power and moves when the brake is depressed. It does not move far enough to disengage the lock function. We did this with the engine running so getting maximum voltage.

I used some silicon spray on the plunger, letting it soak for a bit and then depressing the brake multiple times to work it in. I also used a small probe to repeatedly push the plunger in as far as it could go into the solenoid body, hoping to push junk out the other side.

Now the solenoid fully unlocks about 1 out of 5 times. I'm not sure if that's any better than before, but it's not enough to be reliable.

We stopped there. It's not my car and I am not prepared to perform more complex surgery that could lead to unfortunate outcomes.

Now he has a very good idea of the issue and can explain it to his mechanic.

Thanks again for all the insights.

We had to pause this about a week ago for vacations, and we're scheduled to get back into it on Labor Day. I'll post with updates next week.

Art / Dave,

Thank you both for the thorough replies. I'll test for power and grounds in the solenoid circuit, and inspect the mechanism. Fortunately, I have a 93 as well and can make some comparisons.

One additional question: I recall on a post I read earlier this week that someone recommended spraying Brake Clean on the mechanism - it worked for them. I cannot imagine doing that with all the wires and other parts inside. What are your thoughts? Is there any safe cleaner to spray in there if I find spilled soda, coffee, or other crap that I need to loosen?

Thanks!

Once you've verified it's not a basic electrical problem (such as a fuse or faulty brake switch) using Art's notes and diagrams then there are two approaches I'd consider:

a) Try to clean it up to see if it will now work. Detritus (in my case dog hair) can get into the trans shifter housing and possibly collect in the solenoid spring to restrict movement. Peak down if you can to see how clean it looks. Maybe try a vacuum or compressed air to see if you can clear it. Failing that, you'd want to remove it to the bench for testing and cleaning.

b) Disable it, which basically means removing it. They're a major pain to get at and remove, so see if you can figure a way to disable it by wedging/gluing the solenoid back in the retracted position.

I wouldn't be overly concerned about the safety aspect. As much as it's a safety mechanism, you can't simply knock or pull back on the lever to get it out of Park and have the car start to roll if you also released the park brake. You still have to push in the release button on the knob to move the lever and the PNP switch prevents it from being started in gear, plus there's the key lock cable to make sure it's in Park when you remove the key. All the solenoid does is require you to also have the key in the ignition and depress the brake pedal in order to move it out of Park. Any kid goofing around will soon learn you can push in the shift lock override tab to be able to start moving the lever. If this was a manual trans there would be no shift lock solenoid.

If it's no longer functioning you could replace it, but that's a whole lot easier said than done. The shift lock solenoid used only in the '93 240s with AW trans is p/n 9130005 (it's actually #43 in Art's parts schematic when you look it up in a Volvo parts catalog, so go figure as it sure looks like it ought to be #47, which isn't listed in the catalogs). New ones are not available in the Volvo parts chain and you're only going to find used ones in a '93 240 parts car. Not a lot of '93 240 parts cars out there.

The shift lock solenoid in the later 940 AW trans shifters is similar, but not identical, to the '93 240 ones. In one of my 940s it started misbehaving. First time, a cleaning got it going again, but the second time I decided the mechanism was worn so succumbed and removed it. I don't like disabling safety features either, but after doing it to one 940 I won't hesitate to do it in my other 940 at the first sign of trouble.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

It looks to me, reading your post, you've done due diligence to eliminating the most common electrical reasons for the shift lock failure, leaving only a few possible external electrical possibilities, such as: an issue with the relay contacts, or wiring to and from the solenoid and relay. My approach would be to get the cover off and using a sharp probe, be sure the solenoid is indeed getting battery voltage across its winding; that its ground and source from the shift lock relay is there.

Reason I stress this, is the solenoid is a simple and reliable component with a surprisingly hefty price tag, and no fun at all to get to and replace.

Mechanical reasons for this failure mostly involve rust or spilled drinks. Here's a map of the electrical connections. The map is from a '91, when these safety retrofit gimmicks were ordained, but the map is the same through '93.



Now the shifter for '93 is mechanically new that year, and a one-year build. I've never had a '93 torn down so here's the parts diagram for it. #47 is your target.



I've never seen this repair/replace described in any manual, and I've got a collection of them. I'm not sure how relevant the following is, but it would go toward showing just how many tools it takes to get to all the pieces from a '91 automatic transmission shifter. I'm not sure they made it that much easier in the '93 and final version.





--
Art Benstein near Baltimore

"If you can't fix it with a hammer, you have an electrical problem." -vwbusman66

Check the owner's manual for a description of how it should work.