Land Rover Repair: 2001 Range rover 4.6 HSE gearbox, friction plates, forward gears

Question
Hi Nigel,

Can you please help me with reasons for a 2001 4.6 HSE gearbox not going
into Drive only in reverse, the only work done on the gearbox since the fault
occurred is an oil change. since the oil change the gearbox will not go
forward. Does this year and model have a computer that can tell it what is
wrong (with correct software), as part of this am I correct in thinking that the
oil is only for the gears and operation of clutches not as part of the friction
plates?

Thanks for your help

Simon.

Answer
There is a computer for diagnostics, but if there was a transmission fault code, the transmission fault light would be illuminated.

The fluid lubricates and powers the complete transmission. Due to the fact that there is no dipstick on the transmission, the fluid level cannot be readily checked.  If the fluid is low, it will burn out the friction plate seals (clutches).  If the fluid is extremely low, in severe cases, you can pick up reverse, but no forward gears.  

If you top up the transmission fluid, do it with the engine running in park.  If topping up the fluid doesn't work, it is probably a one-way clutch (sprague) problem.