02 XC70 with 130k miles.
When I first bought the car 4 years ago with 118k, after 30 minutes of driving the trans was spinning out of gear, slamming, clunk on downshifts, etc. Replaced the fluid, the car slowly adapted and the shifting smoothed out after @2500 mi. No problems for the last 7000 miles except when driving up a long hill to the ski resort. About 50% of the time, the car would get to the top and then throw a P0735 (5th gear incorrect ratio) and go into limp mode. I'd pull over and stop for about a minute, start the car up, my gears would come back, and I'd be on my way again. The transmission was shifting with no perceivable issues so I really didn't know what to make of it.
This summer/fall the trans was shifting better than ever, "almost like new" I told myself. Going to the ski resort, my XC flew up the hill no problem with power to spare. At the top, though, there was that pesky P0735 code and limp mode. When I turned the car off and started it back up, this time the gears weren't coming back and I was getting "-.-". To make matters worse, the P0735 code has now started coming on during regular driving and throwing me into limp mode. I'm also getting another code, P0700 (general transmission fault). Unfortunately, I've done a lot of driving in 3rd gear pulling away from stop lights, etc.
I decided to flush the trans fluid again (10k mi. later) but this time drained 3+ quarts from the pan. The top of the drain plug was covered with gray silt but it didn't seem like an alarming amount. There were no pieces or chunks of the trans in the oil. Although the oil was dark burgundy and needed to be replaced, the fluid change didn't stop the trans from going into limp mode. I should mention, every time the car goes into limp mode, if I wait several hours or overnight, when I start the car up again I have all my gears and the shifting is fine until the code returns.
So I've bought a VIDA/DiCE setup and started collecting info. First I reset the Trans Fluid Counter. I also checked the fluid level and at 80C it's right on the Hot Max mark. Now I'm driving around with VIDA running and monitoring various transmission parameters: Fluid Temp, Gear Ratio, Expected Gear Ratio, S2, SLU, SLT, SLS. Sure enough in 5th gear with an expected ratio of 1.03, the actual gear ratio is fluctuating much higher. The other 4 gears are not deviating much from their expected ratios. VIDA has also indicated that I need to upgrade the TCM software to 30677036.
Unfortunately, while dealing with this latest trans issue, another problem has reared its ugly head. Above a fluid temp of 55C, the trans starts slipping in all gears. This is something new I haven't experienced with this car before. Yesterday, the fluid temp was 70+C and I was barely able to pull away from the stop light. Had to use my flashers to warn the driver behind me! Took the car for a test drive today and the car shifted great with no problems. Held the speed to about 40mph to keep the car from going into 5th. Once the trans fluid temp hit 55C, I could feel the trans starting to slip again as it went through the gears.
Obviously I have no plans to replace the transmission ($5000+). These are the options I'm considering:
1. Install a HEAVYDUTY trans cooler with Magnafine filter. MY XC loves running at the lower fluid temps but is it reasonable to believe a cooler can keep the fluid in the low 50sC? For $100, I don't mind rolling the dice and see what happens. This one on Amazon is 12x12x3/4 in. so I'm thinking it will install in front of the radiator?
https://www.amazon.com/Hayden-Automo...mission+Cooler
2. Tackle the new GM valve body replacement procedure. To me, this is the real crux of the issue and reason for this post. Can my shifting problems be cured with a new valve body or is there significant damage to the transmission internals - bands, clutch plates, etc.? Again, the trans is slipping in all gears above a fluid temp of 55C.
3. TCM software upgrade. I don't have a relationship with a dealer and I think the nearest is about a 45 min. drive. There is an independent shop nearby who might have the ability. I'm sure the upgrade would be an improvement but I'd be skeptical it's going to solve my problem.
I want to thank everyone on this forum for all their help and support over the years. Without you guys, I would have abandoned this car by the side of the road years ago!
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