Welcome to the forum, Peter!
When you take the battery lead off, you should press the brakes to consume the remaining power in the system - the ECU will retain a small charge for up to half an hour otherwise. Pressing the brakes forces that charge to dissipate through the brake lights.
If that doesn't work then the ECU is writing the information to non-volatile memory and we've all got it wrong. I suppose it's possible that Nissan also made some changes so that we HAVE to use the reset procedure - which is here:
Original post:
Exhaust mod with DPF page 2 post 27081
Modifications to refine procedure are in
bold.
D40 ECU RESET PROCEDURE
To carry out the reset do the following:
Warm up the vehicle to normal operating temperature then turn the vehicle off.
Turn ignition on so all dash lights come on.
Wait 3 seconds.
PUMP accelerator pedal 5 times within 5 seconds....
With foot now OFF accelerator wait 7 seconds...
After 7 seconds press and hold down accelerator pedal for 10 seconds...
After 10 seconds the Engine Management Light will start to flash, at this point remove foot from accelerator.
The Nav is now in diagnostics mode, so let the EML flash for a bit. Then press and hold the accelerator pedal down for more than 10 seconds - this will then reset ECU and fuel pump etc and put them into learning mode.
Holding the accelerator for that long ends the procedure.
From
D40 Fuel Economy page 26 post 36741:
DO NOT TURN THE IGNITION OFF. Take the vehicle for a nice gentle drive, go through all the gears and then shut the vehicle down to finish the learning process.
NOTE: When the EML light is flashing, this is listing possible fault codes... so if you know how to read the fault codes or know the sequences then you can figure out any possible faults with your Nav with out getting the dealer to do it!!
From
D40 Fuel Economy page 26 post 36627:
Seeing 1 set of 10 slow flashes followed by 3 sets of 10 flashes fast means there are no faults found or stored.