vs calais fuel economy shot. oxy sensor

[Stewart1000]

hi all.
i just bought a new car
it's a: vs calais series 2 v6.

the ecu is throwing codes

Code 12 - System Pass (OK)
Code 63 - LH Oxygen Sensor (O2) - No Signal
Code 64 - LH Oxygen Sensor Lean (O2)
Code 76 - Air/Fuel ratio variation between left and right banks

i get around 19-20l/100km and thats being very light on the throttle. (i believe i should get around 15l/100.)
driving on a flat road the fuel read out is about 10-12l/100km

i believe the left bank is on the drivers side of the.
i have cleaned the plug and replaced the oxy sensor, reset the trip computer and the readouts are if nothing has been changed.

any advise on what to check next would be great.
also, how do i clear the error codes from the ecu?

i will check back tonight.
thank you very much, Stewart.

[hako]

You need to remove the battery for 30 secs to clear the old codes...or pull the engine fuse for the same time (easier).
Good Luck.

[vnss5ltr]

couldnt have said it better myself

[Jordzz]

mmm thats odd my calais fuel econ was 13.9l p 100kms that was with heaps of throttle also lol
hope you clear it soon champ

[fonzo]

my series 2 berlina is getting this type of econonmy. was bad with old oxy sensors and is worse with new ones :S