change won't hurt, but be aware that the 6 speed box has a special filling procedure. It must be completely drained and then filled with the exact, correct measured quantity of
. If you fill until
overflows from the filler (the normal method) you will overfill the box and it will fail. The box also requires special (and naturally, very expensive)
, usually only available from Renault dealers.
Your fuel economy seems rather on the low side for motorway driving, but might be sensible for urban. Mine tends to drop to low 40's if I'm doing a fair bit of around town driving in combination with the motorway. Try driving at a steady 70mph on a clear road, and resetting the trip. Give it a while to average out for the ups and downs in the terrain (this makes a big difference.) I can manage low to mid 50's at this speed.
The Xenon could be the ballast or the bulb. The cheapest way to find out is to swap over the bulbs and see whether the fault follows the bulb.
Service interval reset is straightforward enough. There are two possible methods, depending on whether or not you still have the separate 'trip reset' button sticking out of the speedo dial. If you do have this button, cycle through the trip computer options until you see the service interval display. Press and hold the reset button - the display will initially flash 0, then flash 18000, then go to steady 18000. Release the button.
If you don't have the trip button, then (after cycling through to the service display) just hold the cycle button until the display shows a steady 18000.
When it comes to
changes, I'd go for 9K if you do a reasonable amount of motorway miles, dropping to 6K if you do mostly urban driving. Renault's official
change interval for the last of the 1.9 dCi's is 9K, though they claim this is because of the particle filter (which wasn't fitted on the earlier ones.)