e320 cdi airbag fault,

[adaptorman]

hi all bought my dad a merc e320 cdi , hes happy with , but ive an issiuse with the abs light staying on , we havent had a problem , until the car was left a couple of days , any advise ,or if i can buy a cheep scanner to check for faults

also if anyone can point out main problems with the car , as ive oready removed rear axle and replaced the bushers along with 4 new coil springs,and services the engine , but im a little confused were the automatic gearbox check leavl is?