Four of its high-speed 175 Coradia train units have been taken off routes along the north Wales coast and to Manchester.
Work on its 150 class of diesel trains is also under way.
Arriva Trains said as a result "some affected peak time services have been busier than usual".
The Coradia trains are the fastest in the fleet operating at up to 100mph on the lines from Chester across to Holyhead, and are between 16 and 17-years-old.
They pull two and three carriage trains.
"We can confirm that four of our 175 units are currently out of use for corrosion repairs, also our 150 fleet is undergoing corrosion repairs," said a spokesperson for the operator.
"We will not be sourcing any extra capacity due to the timescales involved and lack of availability and there are no plans to use the loco stock on the weekends.
"We regret any inconvenience that this has caused to our customers whilst we carry out this essential maintenance work."
The rail company said it hoped all the maintenance work on its trains would be completed by the summer.
Rail operator Arriva Trains Wales has been forced to pull some of its fleet out of service to deal with corrosion problems.