[Steve Tinker]

It won't make any difference to your low level CEL. All the cap does is maintain pressure in the system - a failing cap seal lets air into or coolant out of the system.......

To complicate matters, you could have a problem with your engine compartment blower fan, which also displays a flashing light, as follows....

Four functions of the coolant warning light:

1. Engine coolant level too low
— light flashes slowly (0.5 Hz)
2. Engine compartment temperature too high
— light flashes slowly (0.5 Hz) (engine compartment blower might be faulty)
3. Engine coolant temperature too high
— light is lit; pointer on the right
4. Temperature sensor at water outlet faulty
— light flashes rapidly (1 Hz); pointer on the right

Note
The temperature warning in point three is indicated if the conditions "engine coolant temperature too high" and "engine coolant level too low" are present simultaneously
(1Hz = 1 flash per second. 0.5Hz = 2 seconds per flash).

Hope this helps.