I've recently bought a '93 850 with a 2,5L 125kW engine and an automatic transmission. The car used to belong to a friend of mine a few years ago, and knowing that at that time the car worked great, I bought it when the chance came.
I am experiencing problems with both the transmission and the engine, and since I am not certain whether the problems are related or not, I will combine them into a single thread.
First of all, the transmission isn't working well at times - the problems include rough shifting, delayed shifting, not shifting over 2nd or 3rd gear (revs at about 2500 at 35 mph), not shifting anywhere else than the above gear, even while starting to move, not shifting into reverse after driving for a while (shifts after stopping the engine) and losing traction completely while in D. While these problems are present, the arrow light on the dashboard stays on, blinks, or glows more or less dimly, sometimes at the same time when blinking.
The first action we took was to flush the transmission, since the oil was badly burnt and it seemed to be overfilled as well (we drained about 4 liters or slightly more). After changing the oil and erasing the DTCs in the A1 socket, the problems seemed to disappear for about 40 miles or so, so I thought that the oil change solved it for me.
The problems reappeared though. Every time the problems come up, the OBD socket A1 reads the code 131 (Open Or Short To Ground In Line Pressure Solenoid (STH) Circuit). Sometimes deleting the code solves the problems for the next 10-20 miles, sometimes the arrow light in the dashboard starts to glow again shortly after starting the car (I am quite certain that the light should either stay on or blink, not glow).
We followed the diagnosis instructions found here, checking the solenoid resistance, and found it to be 4,5 ohms, so that part should be OK.
Another symptom with the transmission is that the OBD A1 socket is not functional most of the time - it tends to light up or glow immediately after the connection is made, making DTC reading or erasing impossible. When it is operational at times, it still shows the 131 code, which can then be erased. The other sockets are working as they should at all times. As we thought that the problem might be related to the transmission problem as well, we tried to locate the cause, but found all the wiring to the control units to be good, and the control units and their connections seem to be in good condition as well. Then we tried swapping the transmission control unit for another one from a 1993 automatic 850 (the markings on the case weren't identical though), to see if the control unit might be the cause of the problem, but that didn't change anything - the transmission still experienced problems and the A1 socket still didn't work as it should most of the time. We then removed the ignition and engine control units to see if those interfere with the A1 socket, and found that the socket worked great if the other control units weren't present (the light didn't have even a dim glow). Placing the ignition control unit back seemed to keep the A1 operational, but after putting the engine control unit in as well, it started misbehaving again. We then replaced the engine control unit with the one from the same car we got the transmission control unit from, to see if the engine control unit was bad, but the problem didn't disappear.
Since both the arrow indicator in the dashboard and the A1 socket glow either dimly or brightly from time to time, I get the impression that they are both part of the same problem, but I am not sure where to look further. Any ideas?
Now to the engine problem. I didn't notice anything at first, but when the transmission had already started acting up, the engine sometimes started stuttering when idling at traffic lights and so on. A while later it started stalling right after starting up, so that it would need some throttle just to stay going, and when the throttle was released, it would start to stall and then rev up slightly, with ever larger amplitude, until it would stall. Since the transmission problems were there as well, I didn't notice anything else at first, and thought that it might just be the IAC valve needing cleaning, but a few days later the engine started losing power while driving, so that it was noticeable even with the transmission problems - at first it just accelerated weakly, but then the power loss became apparent while simply holding speed. The engine wouldn't respond to throttle for a few seconds and even stalled. After that drive the A2 socket gave me the 511 DTC, which should stand for Long Term Fuel Trim Idling, Lower Limit, which, as I understand, means that the fuel mixture was too rich and the ECU had tried to make it leaner as much as possible, but had hit the lower limit (there was a gasoline smell at the car after that drive as well). After clearing the DTC, the problem disappeared immediately. I looked the stalling problem up at these forums and elsewhere, and found that someone had had a problem with the airbox thermostat being stuck at hot air intake. The next day we looked that up, and my thermostat was not working either, heating up the airbox and the MAF. We replaced the thermostat and the valve started working as it should, so I thought that I had solved the engine problems (we cleaned the distributor and the IAC valve as well), but after 20 or so miles of driving, the idling started to get worse again, and a bit later the power loss problem came up again. I checked the A2 socket, but there were no DTCs there, and since I had to move on, I drove the next 20 or so miles as best I could, but soon the powerloss wasn't intermittent anymore, but more or less constant, with the engine having troubles holding any speed and stuttering all the time - losing power completely and getting some back 2-3 times a second, as if the throttle was being played with. When I finally got where I needed to, I checked the A2 socket again, and got the 511 code again, and after clearing it, the engine worked fine again immediately. I did a short test drive, and after 5 miles or so, I noticed the idle getting worse again.
That should be pretty much it for now, so after this long post, does anyone have any ideas on what I should check next?

 

Dude, way too much here, can you possibly break it down into smaller parts?

 

Ok, perhaps I did jam too much information into 1 paragraph.

I have a transmission problem and an engine problem.

A) The transmission has an intermittent problem, where it shifts rough, shifts late, doesnt shift higher than 2nd or 3rd (not sure which), doesnt shift anywhere else than 2nd or 3rd even when starting to move, doesnt shift into reverse after driving for a while, sometimes acts as if its in neutral while in drive.

-It reads the 131 code in A1 after the problems appear. (Open Or Short To Ground In Line Pressure Solenoid (STH) Circuit)
-After clearing the code, sometimes works perfectly for about 20 or so miles, which leads me to think that the problem itself isnt constant, but once it appears, it tends to make the transmission go into some emergency mode, making performance even more bad.

While the problems are taking place, the arrow indicator in the dashboard either lights up, blinks, or glows slightly, as if it had a bad signal. I am quite sure that it isnt meant to glow.

The other part of the problem is the A1 diagnostic socket itself, which is unoperational most of the time, lighting up the lamp as soon as the connection is made. The lamp may light up completely or glow more or less brightly, and there is no response to input.
At times it does respond to input (when the glow isnt too bright), and then it works as it should, giving the codes and letting me clear them.

-We started up with flushing the transmission fluid, which was badly burnt and about 0,5 liters overfilled. It solved it for about 30 miles, and then the problems returned.
-We have cleaned the PNP switch.
-Trying to solve the diagnostic socket problem, we checked the wiring to the control units and the connectors of the units, which were all good.
-Replacing the transmission control unit with another one didnt change anything.
-Removing the engine control unit fixed the A1 socket problem, but putting a different one in instead of mine still gave the A1 socket problem.

This leads me to believe that the problem is not directly control unit related. The transmisson problems in general didnt disappear with control unit replacements.

-The line pressure solenoid circuit (read from the control unit connector with the unit removed) reads a resistance of 4,5 ohms, which should be ok.
-I am not sure how to check the voltage supply to the solenoid, since it comes from the transmission control unit. A transmission diagnostic pdf that I found also suggested checking the signal and control wiring, but I am not certain what they meant with that either, because the solenoid has just 2 connecting wires originating from the control unit.

B) The engine has a slowly deteriorating and then resettable problem that starts out with bad idling and works all the way up to near-complete power loss and stuttering while driving.

-After the problem has turned so bad that it is nearly impossible to drive and hold any speed, the A2 socket reads the 511 code (Long Term Fuel Trim Idling, Lower Limit), which should mean that the engine seems to run rich and the ECU has tried leaning the mix until it hit the lower limit. At the same time the engine does seem to be running rich, since there is a smell of gasoline around after driving.
-After clearing the code, the engine starts running perfect immediately (regardless of the transmission problems).
-The problems start to reappear after about 5 or so miles, starting with bad idling and needing a touch of throttle when strating. In 20-30 miles the problem starts to effect normal driving, and in another 20 miles makes driving impossible, at which time the code is present again.

-We replaced the airbox thermostat, which had kept the valve on hot air at all times, heating up the airbox. The airbox doesnt heat up anymore.
-Also cleaned the IAC a bit and the distributor cap.

-I am not sure where to go from here, since I couldnt find much information for the 511 DTC.

I am also not sure whether the problems are completely separate, or if there is some connection between them.

 

Okay, I found some information on the engine problem by searching the long term fuel trim on other Volvo models, and it seems that the possible causes are as follows.

This gives me something to work on - most likely the MAF sensor has been damaged by the hot intake air.
But the transmission problem is still open.

 

If you've flushed the tranny with Dexron-III/Mercon to the correct level, the tranny may be shot. You can try cleaning all electrical connectors leading to the tranny & TCM with a can of contact cleaner but either a solenoid(s) has gone south, the internals have gunked up with old fluid or the clutches have gone south.

Volvo generally does not recommend tranny overhauled and replacing with known good used unit would be the best bet. As a last resort, you can try Lucas tranny fluid additive or try flushing with synthetic fluid (I do not recommend synthetic ATF for a normally-operating tranny).

Sorry I couldn't help you better.


JPN

 

The tranny issue is either on of the Solenoids (Either S1 or S2) inside the transmission. That said, it could also be an issue with the transmission computer itself. The reason I say this is because of the issue you are having with the A1 port.

 

Thanks for the input. I do have a few more ideas on the subject.
First, I suspect that the reason for the burnt transmission fluid is the problem itself, since I am moderately certain that the previous owner (who bought the car from a friend of mine) didn't really mind the transmission problems (which started to appear when he was driving it), and continued driving as usual, which probably included driving with the 2nd or 3rd gear at too high speeds and burning the fluid in the process. Since the problems were present when the fluid was OK, I wouldn't rush to assume that the main problem is blockage in the hydraulic system.
Fcpgroton, why do you think that the problem is in the shifting solenoids, when the DTC concerns the line pressure solenoid?
Anyway, I would rule out the transmission control unit, since the other one I tried on the car, while not completely identical, gave me the exact same symptoms.

With the research I have done, my best bet at the moment is a faulty connection between the transmission control unit (or another control unit, since they all seem to be interconnected in part) and the battery. The wiring diagrams I've found suggest that the control units draw voltage straight from the battery without any fuses or without passing through the ignition switch. I am hypothesizing that if there is a bad connection somewhere, the control units may not be getting the correct voltage at some times, which is causing the mess with the A1 port as well as the line pressure solenoid, and the latter would also mess up the shifting, since it should also be the part that switches on the emergency mode in the transmission. Would that make sense?
I will try to measure the voltage at all the battery connections of the control units tomorrow, to see if they differ remarkably from the battery voltage, and visually inspect them as much as possible.
I believe there is a control unit diagnostic tool that goes between the control unit and its socket, which allows real-time diagnostics while driving, but I am not sure whether I will be able to get hold of it, but since the A1 port is messed up with just the ignition switched on, I should find the possible problem without the engine running as well.

 

Since I haven't been able to solve either problem, I will bring this topic up again.

Concerning the transmission, I did measure the voltage at the TCU pin coming from the battery, and I got the battery voltage, so the connection is most likely good (or working intermittently, although I am not sure how I would check that).

A bit more driving has shown me, that while the arrow light is not lit at all, the transmission works perfectly, and it works more or less good when it is blinking, but as soon as the "off" period of the blinking starts to glow as well or the light just stays completely on, there is no upshifting beyond what you would get with the stick at "L" (regardless of the actual postition). Driving around slowly with low gears at some point results in the arrow light going off, and the transmission starts shifting fine again. Sometimes the period when it does shift is so short, that it only manages to shift up to the third gear (as if the stick was at "3"), and sometimes it shifts all the way up. If the arrow lights completely up again, it doesn't force a downshift, but if I slow down to lower gears, I won't be able to get them shift up again.

Since the arrow should be lit when the stick is at "3" or "L" anyway, it does look as if the transmission thought that its not at "D" at that time, but since the PNP switch has been replaced with a cleaned and greased one, I don't think that it is caused directly by that. Also, while the transmission is stuck at "L", I can't shift into reverse after driving, and I need to shut the engine off and restart it, so I could get into reverse. I checked the reverse lights, and they do light up even when the transmission doesn't shift in.

My question would be - can all this be caused by faulty solenoids? Would the transmission provide feedback to the dashboard light and make it act weird?

About the engine problems.

I tried swapping the MAF for a working one, but over time, the engine starts working bad again, finally resuting in either a idle or normal fuel trim maximum or minimal DTC.
I also disconnected the HO2S wire, and the car runs a bit rough, but it seems to me that it doesn't save the fuel trim settings anymore, so that if the engine starts to run real bad, I can just shut it off and after restarting it, it works normally (as normally as it can without the HO2S).

Since the problem is there regardless of the MAF and HO2S, I would rule both of them out from being faulty, but what would the next thing to check be?

Would a faulty engine coolant temp gauge show up at the dashboard indicator as well? (the dashboard indicator works normally at all times)

Should I suspect fuel pressure? The spark plugs? Engine coolant temp sensor? Crankshaf/camshaft position sensor?

 

You do realize that the arrow is indicating that your overdrive is turned off, which would be why it sounds like you don't pass third gear. Just hit the button on your gear shift (at least that is where mine is) and turn it off.