850 Transmission in Limp Mode

[1800ES]

Well, last night was pretty much a complete waste of time and money. Got the brand new PNP switch installed with no trouble at all, made sure it was properly alighned, took it out for a little test drive, and within 3 miles code P0734 was back again. What a complete disappointment. To top that off, we discovered after the drive that the transmission dipstick tube had not been properly reseated when we reassembled everything, so I lost some ATF fluid while we were on the short drive. No clue how much. It was dark outside and we were too frustrated at that point to really care.

On the plus side, we also swapped in the new MattyMoo ABS module while we had easy access. The only hang-up here was the E5 torx bit being defective. It was brand new in the package, but it looks like there was a problem with the casting and it had a flat spot where one of the "points" should have been. Ugh. Had to spend over an hour driving around to every store in the area we could think of trying to find one that had an E5 in stock. Fortunately, Harbor Freight did. At least the ABS/Tracs lights did not return while we had it out for the short test drive, so I'm hoping that problem is at least resolved.

[1800ES]

Had a little bit of time yesterday, so we worked on getting the transmission dipstick tube properly reinstalled, including replacing the o-ring. We topped off the fluid level (fortunately, I hadn't lost too much), and took it out for another test drive.

Same thing again. It shifted beautifully for about 3-4 miles, which included several complete stops along the way, and then while driving along at a constant 45-50 mph, the transmission arrow light began flashing again, followed shortly thereafter by the check engine light and code P0734 once again.

Does anybody know of anything else that could bring up that code other than the PNP switch, which is brand new at this point? I'm not getting any other codes, but wonder if it could have something to do with the S1 and/or S2 solenoids.

[Billc1015]

Sounds like debris is getting sucked up into the filter causing it to clog. After shutting off the car the debris will settle down again which is why it will shift fine for a little after you start it back up. In both the transmissions I took apart, clutch material from the internediate band came free and clogged the filters. It would require a removal and disassembly to fix.

[BigRed]

Have you tried cleaing the codes while out driving it? I think it may be a good diagnostic step. Clear the code(s) will out driving then continue driving and see how long it takes to enter again, may give indication as to root cause.

One scenerio is debris getting sucked up clogging filter, which results in an A/T malfunction and recorded as a fault with TCM which puts it into Limp Mode. If that were the case, and you cleared the code while out driving I would expect that the malfunction resulting from the clogged filter would re-occur near immediatley.

Another possability is the solenoids from time to time are sticking. In that case I would expect that the A/T would continue to function "normally" for much longer after clearing the code(s) while out driving.

Yet another possability is some electrical sensore problem. In that case I would expect it to be almost random, that the malfunction would re-occur near immediatley or maybe it would last for miles or even days.

So try clearing the codes everytime it goes into Limp Mode for awhile and keep driving. See if you can find any consistency to it.

[boosted5cyl]

I dont think the VAG-COM software will work. Ive had no luck with the "UBD2 icon" in VAG-Com if thats what you are thinking of. You can use the VAG cable with VOL-FCR however. Only caveat is that VOL-FCR will only look at COM1 so be sure that you have your VAG-COM virtual serial port setup as COM1 in device manager.

I wonder if something got stuck in the transmission fluid cooler. Maybe bypass it and go for a short drive?
Other than that it might be worth doing a line pressure test as documented on page 8 of this PDF: http://www.volvoclub.org.uk/tech/servic ... gnosis.pdf

I have no idea how much such a pressure gauge costs though.
Maybe pump is on the way out? Im not sure where the filter is in this AW tranny, or it if even has one inside but if it exists the tranny needs to come out to gain access to it I would think.

/edit. Here's a transmission\oil pressure gauge for a little over $30 + shipping. Don't forget to buy it though the MVS link
I know nothing about it so buy at your own risk.
https://www.amazon.com/Advanced-ATD-5550 ... B000OUZBZ0

[boosted5cyl]

Also, with the TRACS\ABS warning light, I wonder if you have lost a signal from a wheel speed sensor? It varies from model to model but I believe some take their speed reading from the transmission and others from the ABS sensors. In either case, a bad signal from a speed sensor would definately confuse the transmission.

[1800ES]

Thanks for all the suggestions! I am not driving the car at all right now, so driving it and clearing codes as I go probably isn't going to happen. My commute is way too much stop and go driving and I don't want to put any more strain on the transmission trying to get moving in 3rd gear. Not to mention, I don't feel safe trying to get through some of the intersections at a snail's pace. If it makes any difference, it does seem like the code only reappears when the engine/transmission have gotten warmed up.

I definitely would like to run through a bunch of the diagnostic tests spelled out in the write-up from the UK site. We've already printed that whole article out for reference. As far as checking the filter... Where exactly is it located? I'm looking at an exploded parts view of the transmission on volvopartswebstore.com and I don't see anything that's labelled as a filter. If we get in there to check it, does the filter get cleaned, or does it have to be replaced? If so, where can I buy a new filter? I don't see one listed for sale on any of the usual parts sites.

Unfortunately, I can't afford to dump any more money, or worse, time into trying to get this thing fixed right now. I'm in the middle of a DIY home renovation and I've wasted multiple days of what could have been progress on the house, only to get nowhere with the car. So it's going to get parked on the side of the garage now for at least a couple weeks until we can finish rough-in and get through inspection with the township.

To answer a few more comments, I'm not trying to use VAG-COM itself, but I am hoping to at least be able to use the cable. I definitely want to have VOL-FCR up and running when we get back to trying to solve the problem.

The ABS/TRACS lights did not return during the last test drive. I'd like to think replacing the ABS module with one rebuilt by MattyMoo has at least eliminated that problem. Speaking of which, I need to get my old one in the mail to him...

If anyone has further suggestions, I'd love to hear them. I'll post an update when we are able to spend some more time trying to resolve the problem.

[MoVolvos]

What was the color of the Trans fluid when you flushed it?

Is this the hose you flushed it from except for the older style clamp?


What did the STUFF on the Magnetic Drain Plug look like?

Did the coolant ever make it into the Transmission from the Radiator?

Blessings,
BKM
-

[dbeckwith]

Try driving it with gear selector in 3rd and see what happens. It won't fix anything but you may be able to narrow the search.

[BigRed]

If driving is out of the question due to safety reasons, how about running it on stands...or even just idling in Park? If it's debris clogging, I'd still expect that to happen. If it were a wheel sensor, then I would expect it to not happen. My '96 was still suffering Limp Mode after redoing ABS Module and replacing Solenoids. There's a sensor on top of tranny I disconnected, shifts fine ever since.

I have a $5 eBay serial VAG-COM cable that works with VOL-FCR.

If it becomes too much of a headache...I'd like to have a Platinum Edition!

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