ABS light flickers ..

[dads Taxi x3]

Hi all .  My son just showed me that in the last 2 or 3 days .when he turns on the ignition on the  2012 aygo all the dash lights up but  the ABS light flickers very fast but not full light  .I mean it's faint light not fully bright like the others . 

Soon as it starts the car    lights go off like normal. When he's driving the car they  don't flash or anything .. 

Only as he turns the ignition one once it's started al the dash lights go off like normal . 

Does anyone have any idea what's up with it . 

I thought it be Could it be the start of one the sensors ..  but if that the case would it be when driven .. 

Any help will be fantastic.  Thanks .  

[DJ123]

i'd get a code reader on it and see if there is anything stored. That'll definitely be the case if a sensor is on the way out, or has erroneous readings.