Constant Speed Solenoid behaving erratically

[Cees Klumper]

Since last week my CSS has been acting up: when putting the car (an automatic) in Drive, sometimes the CSS is activated, and sometimes it isn't - when it isn't, there is no power going to the device (so it's not the CSS itself). When I put the car in Reverse, the CSS is always activated and works just fine.

So I figure the problem must be either in the wire that goes over the top of the transmission, OR the switch that the wire attaches to is becoming defective. I think so because there are two separate switches for "D" and "R" and since "R" always works, and "D" is erratic. I checked out the wire, and it seems to be just fine. So I am planning to remove the switch (bolted to the side of the transmission) to check it out. I have the following questions, hopefully someone knows answer(s):

- which of the two switches governs the "D" CSS activation (left or right hand side of the transmission, looking forward) - I assume it's the right-hand side one, but would appreciate advice

- anyone else had this problem?

- are these switches repairable?

- when I remove one or both switches, can I expect transmission oil to come pooring out?

- possible other causes, given these symptoms?

Thanks!

[Cees Klumper]

No replies yet and I am not surprised since I don't recall this particular question ever having come up before (although I don't remember or see everything of course).

As I was shaving this morning (no kidding) I realized it's been quite a while since I checked the transmission fluid level - 4 years to be precise. So it could well be that simple: low fluid level affecting the operation of the hydraulic switch that activates the CSS - silly things like that have happened to me before! I will try it this evening and will report back. I have seen these switches are available new at around EUR 100 so not the end of the world either.

[graphic66]

To test this you need to have the car running and you need access to the two switches. I put mine up on jack stands, parking brake on, and started the car and put it into drive. You then take test light or meter and run a wire from the positive post on the battery down to the transmission. With the car in gear the switch grounds out the wire and activated the CSS. So you just hook you tester to the hot wire from the battery and the negative lead on your tester to the switch on the tranny. It should light the test light or get a meter reading. Simpler, you can just check with an ohm meter for continuity from the switch to the chassis. Be sure to first, with the car running make sure you have constant + power to the CSS. The car must be running to test the switches on the tranny as the pressure in the tranny activates the switch. To test the CSS you can also just ground out the negative lead to the CSS with the car on and in park. It should activate. I think the switch on the left side of the tranny is the forward switch. My car just did that and I put a switch from my parts transmission in and it was fixed. I now want to autopsy the old switch to see if you can fix them. Very easy job. Just do some testing and remember you are switching the negative lead to activate the CSS, not the positive lead. The + lead is always hot with the key in the run position. My guess is that the left side activating switch on the transmission is bad. A temporary fix would be to just switch the switches so your reverse didn't activate the CSS until you could get a replacement. It is a pain at stop lights without it. But in reverse you are generally not sitting and idling.

[graphic66]

And no fluid will not come pouring out when you take the switches out unless your car is running.

[Cees Klumper]

Thanks very much for the tips Graphic66.

I checked with the car in gear, parking break (firmly) on and there was no power coming to the CSS, and then all of a sudden there was.

Then I checked the trans fluid level and indeed it was just a bit too low; I added .4 liter which put it at the top mark. It shifts better, smoother, but no change in the behavior of the CSS. Car in reverse: perfect CSS action every time. Forward: works fine when cold, but as the engine warms up it starts becoming 'hit or miss'.

I will check out the switches and swap them out to double-check, but I think we're onto the problem.

[Ziggy]

quote:Originally posted by cees klumper

 I realized it's been quite a while since I checked the transmission fluid level - 4 years to be precise.

4 years ! [:0] Cees, I would advise you to change the AT filter and oil as soon as possible. ATF ages, gets contaminated and such, to keep the transmission in good shape this should be well maintained. MB states the ATF should be renewed every 2 years or 50,000 km, whatever comes first.

[graphic66]

Now, when you say no power was coming to the CSS you mean that the transmission switch was not grounding out or that the positive feed to the CSS was erratic. As I said in a previous post, the switch on the transmission just grounds out to activate the CSS. My guess is a bad switch on the tranny, or the hydraulic passage in the switch could be plugged. You could pull the two switches out and try cleaning them out, switch them around and see if it works at all. I will try and take apart the one that failed in my car and see if you can fix them. Again, the CSS is supplied with constant positive power from the battery when the ignition is on and activated by the switch on the transmission grounding a wire out. I don't have my schematic in front of me, so I'm not sure where the positive lead is fed from. Take your meter, with the ignition on and check for power to the CSS by hooking your negative test lead to a good ground, then touch your positive test lead to the CSS. You can then determine the "hot"+ lead feeding the CSS. You can then just jump a wire from a good ground to the "not Hot" negative post on the CSS, this would also be the wire going to the transmission switches. That should activate the CSS and tell you that the problem is somewhere between the CSS and the transmission. Also make sure you have a good ground to your engine and transmission. Very unlikely your problem, but I believe there is a ground strap between the chassis and engine.

[Cees Klumper]

Ziggy - I will change the fluid and filter pronto.

Graphic66 - I have not checked the positive lead to the CSS yet, but since it always works on the Reverse gear, I am just about positive (pun intended) that the problem must be with the pressure switch for the forward gears. So I will take both switches off when I change the fluid + filter, and see if cleaning them out does the trick, or if it doesn't, will swap out with a new/spare one. Will report back when I have gotten to it.

Thanks for all the help.

[Cees Klumper]

Well, took a few hours this afternoon to change the automatic trans filter + fluid. Since the CSS was working fine as I was doing errands to get everything up to operating temperature, I decided against taking off the switches and see whether the fluid and filter change would make a difference. After doing the whole procedure (which took me longer than I had expected, mostly because of all of these bolts that hold the transmission oil pan in place, plus the fact that I dropped my wrench into the drain pan full of hot transmission fluid a couple of times!) I test-drove the car and the erratic behaviour is still with me. Most of the time it works, and I can hear the switch clicking actually, that's how quiet the car idles now with the 123 ignition in place (see other thread on that) when it does engage as I put the car in 'D', but sometimes it doesn't. So next step is, when I have time again, removing the switches.

My wife, 9-year old son and I are off to our country house in France tomorrow (via Disneyland Paris), where I have two spare auto transmissions. I will take two of these switches off of those, and use them as replacement(s) for my current (again, pun intended) switch(es). Or maybe the forward switch just needs cleaning; I noticed fine metal shavings in the oil pan (brrrr....) when I changed the filter etc so maybe it's 'just some debris' (bbbrrrrrrrr.........) in there!

To be continued.

[abe280SL]

I had the exact same problem.  I took the switches off and reversed them...then I found out that forward worked well but not reverse.  That confirmed it was a switch problem.  I took them off and with a air hose blew the heck out of them...I put acetone in there and more air.  I did this for a long time and put the switches back in.  Now it makes good ground contact. I dont think you can take the switch apart...if I recall they are pressed sealed. One last thing,  never put the transmission in reverse/drive with the switch out and the car running.....its like a fire hose squirting 20ft of transmission fluid.  Yes, it happened to me.
good luck
abe

[Cees Klumper]

Update - I've been driving the car all week, couple hundred miles by now, after it sat for a week and a half with no action after the transmission fluid and filter change (long overdue) whilst I was on vacation with the family. The CSS has performed flawlessly for those couple hundred miles in both Drive and Reverse modes, so I am going to leave the switches alone for the time being. Maybe the fresh oil was what it needed. The car, which always shifted quite smoothly, now shifts even better, but then I also reconnected a few wires for the 3-position solenoid that had gotten in disarray, so now that is working the way it should as well which will influence the shifting behavior.

[Cees Klumper]

Hopefully final update: swung by Van Dijk this afternoon who, in 5 minutes, swapped out the "D" hydraulic switch at the transmission and so far the issue is gone.