I've recently picked up a 2006 Astra 1.9 CDTI Design 5dr and if I do the brake and accelerator test it brings up two fault codes ECN 161450 and ECN 161600.

Am I correct in thinking that these are immobiliser faults codes? Also what is likely to have caused them?

The fault light isn't illuminated while driving so presumably these are old fault codes. Do fault code readers give you a date as to when the fault last occured?

Also on a possibly related note the unlock key on both fobs works instantly but the lock one sometimes requires two or three presses to work. I'll try changing the batteries in the fobs first but does anyone have any idea what else the problem maybe?