hiclimber

Hello,first post. Longtime Subaru owner. How do I read the trouble codes on my 01 Forester? My 94 Loyale has a little red flashing light under the dash which I use (in conjunction with the shop manual) to decipher the code. Is there an after-market device that I could use. I'm getting the CEL code for catalytic low efficiency (very intermittent) and want to monitor the codes to ensure something else doesn't trigger the light. Thanks