2nd gear is the default gear, called "limp in" mode, that allows you to drive it to a repair shop. When the transmission computer detects slippage in any of the clutch packs, it defaults to 2nd gear. You can still hydraulically select park, reverse, and neutral, but going forward it will stay in 2nd until you cycle the ignition switch off, then restart the engine. The clutch slippage usually occurs during upshifts due to the high engine torque. Lately there seems to be more trouble with sensors and less internal serious problems.
Once the system goes to limp-in, there will be diagnostic fault codes stored in the memory of the transmission computer. Do not disconnect the battery cables until someone connects a hand-held computer, (scanner), to read those codes. Unhooking the battery will erase those codes and the valuable information they provide.
If the clutch plate material is worn off, it will increase the volume of fluid needed to fully apply the pistons. The computer monitors these gradually changing volumes to constantly update shift points to provide nice crisp shifts. There are four volumes that can be read on the scanner to show how much clutch pack wear has taken place. These are called the Clutch Volume Index (CVI).
Friday, January 8th, 2010 AT 4:00 AM