Hi krusejj. Welcome to the forum. Second gear is default or "limp-in" mode to allow you to drive it to a repair shop. As you noticed, it will stay there until you reset the Electronic Automatic Transmission Controller (EATX) by cycling the ignition switch off and back on. Besides the sensors, the computer looks for slippage in the clutch packs. When it detects slippage, (usually during an upshift under load), it defaults to limp-in. Part of the problem is the computer learns how many ccs of fluid it takes to apply each clutch, and as the plates wear over time, it applies one clutch just a little sooner before releasing the previous one to maintain a nice solid feel to the shift. The disadvantage to this is you have no warning the wear is taking place until it can't update the shift timing enough and the symptoms you described occur. Years ago, the same wear would result in engine rpm flare-up during shifts. Often the slippage was so minimal, we never noticed it. Unfortunately, the computer does.
One thing that might help you narrow it down is noticing when the default occurs. If you start the engine and it is already in second gear when you start to move, it is generally sensor-related or an electrical problem. If you start out in first gear, like normal, then it defaults to second gear during an upshift, it is generally clutch slippage. If it always occurs when upshifting into the same gear, you can overcome the problem by accelerating a little harder than normal, then letting off the gas at about the time it's ready to upshift into that gear. That will remove the torque on that clutch pack so it won't slip. Once it's solidly in that higher gear, you can drive like normal.
The way you described it, I'm guessing it's clutch slippage that is just getting bad enough for the computer to detect. That's why it shifts properly some days. It's often less expensive to install a remanufactured transmission because there have been a pile of updated and improved parts developed for it that will be included. To rebuild your old transmission will likely be more expensive if you have to buy all those parts. If you do go that route, you might be able to assist the rebuilder by observing which gears affect the default when the shifts occur and if it happens in more than one gear.
Thursday, April 22nd, 2010 AT 11:42 PM