Experience has shown that it is generally very reliable, however some specific problems have been identified and their diagnosis and suggested repairs are available on this site.

INITIAL CHECKS:

Drive the car until the engine and autobox is at operating temperature. Park on a level surface and leave the engine running. Pull the autobox dipstick and check for:-

A. The fluid level is between the MIN and MAX marks on the dipstick.

B. The fluid is a good red colour when you wipe the dipstick on a lint-free white cloth. Provided that the fluid is at a good level, it is a good red colour and has a clean mineral smell and there is no black debris on the dipstick then the autobox is in generally good condition and should be working correctly.

C. If the gearbox fluid is a good red but there are driveability concerns (rising revs and thumping into gear, slipping out of top gear, torque lockup slipping in and out, Overdrive Light flashing) then there is a driveability concern. If the speedometer is erratic as well then the Vehicle Speed Sensor (VSS) has probably failed, or the wiring connection is faulty and is not necessarily a fault with the autobox.

Meet with another owner with an OBD lead or go to a diagnostics-equipped garage and have them read the Diagnostic Trouble Codes from the On Board Diagnostic system - it may be possible to repair a single solenoid or sensor without reconditioning the whole autobox.

D. If the Autobox is working satisfactorily and the fluid is still a red colour but there is some black sludge gathered round the dipstick then have the gearbox sump removed and the filter changed without delay. You may have noticed the gearbox might be a little sluggish, perhaps a loud turbine noise when moving off from rest: this is the ATF pump trying to pull fluid through the gungy filter. You need a new filter, sump gasket and 6 litres of Dexron II. Action now may save much greater damage.

E. If the dipstick shows fluid a brown colour with a burnt smell (like rancid chip fat) then there is bad news. The fluid has been overheated and/or there is brake band friction surface contamination of the fluid, while black gritty bits are the solenoid seals breaking up. Changing the filter and fluid will be a waste of money because the autobox will fail at some time in the near future. This is so even if the autobox is working correctly - in this case failure may be sudden and total (ie selecting any gear other than P or D immediately stalls the engine), or the 'box will drop one gear after another until it limits engine torque and you limp home at 19 mph. If you find your auto fluid in this state then join the AA or the RAC immediately because you will need a tow at some stage. Have an autobox specialist give you a quote for reconditioning your 'box.

OPERATING CONCERNS

1. If your Autobox demonstrates a heavy vibration when changing gear, similar to driving over a cattle grid then read the page about this fault here.

2. If your Autobox does not appear to choose the correct gear, you lose overdrive 4th gear or the torque converter fails to lockup correctly then it may just need the MAF cleaning - read about it here. 

3. If the autobox is not changing gear correctly and the speedometer is erratic as well then the VSS is suspect and there may not be a problem with the autobox at all.  If the TR sensor is faulty it would also cause faulty changing but the speedometer will remain unaffected.  However, both will generate an error code on OBD so it would be easy to determine which is the culprit.

4. If cleaning the MAF has no effect and the speedometer works correctly then you should check for Diagnostic Trouble Codes (DTCs). It costs between £60 and £90 to have the codes read by Main Dealer, less by a properly equipped local garage, or you can read the code yourself by meeting with an owner equipped with an OBD lead.  Purchasing this lead can pay for itself in one reading. Intermittent and continuous faults with the gearbox solenoids, VSS and the TR sensor would all be recorded.

5. If you have a coolant leak that cannot be traced and the autobox fluid shows rapid deterioration then suspect the radiator: it may be leaking coolant into the auto fluid through the heat exchanger on the nearside.  Change the radiator immediately and replace the auto fluid and filter.

6. If your Autobox is behaving badly (especially after rain or washing) and DTCs are changing or coming and going, then read this article and check your wiring looms for damage before taking it to an automatic gearbox specialist - but note that this is very rare.