ABS Light

[beemerdreamer]

Good Morning People hope all are well,
I could really do with some advise with my X5 abs dashlight,It seems when you first turn the key to ignition all the dash lights light up as normal and go out as normal but if you turn the ignition off & back on again the abs light doesnt light up !!!!
If you leave ignition off for a few minutes then try again the exact same thing happens again,i have checked connections and cleaned sensors etc but does anyone know why it would work first time but not second which would indicate to me that the sensor/wires are not at fault ???
Any Advise would be greatly appreciated