This is probably a 0400 error (and as Dominick points out, all digits matter in error codes). Turn the power off and clean the print heads and cap tops manually. 0400 means that the cleaning pump runs for a certain amount of time in which it expects the damper full sensor to indicate that it is empty. When the pump runs too long it will return this error. Unless there was a head strike, this usually means that there is something that is preventing a good seal between the cap top and the head. Also, if the cap top has not been replaced within the last 6 months, it could be that they need to be replaced as well. The 0020 indicates that this is channel 2 on head 3.
