P0603 code . after clearing it comes back

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car died, replaced 7 yr old battery & drove home, bad altenator but drove car to work (about .5 mile) for 3 days, P0603 appeared intermitently, installed new altenator and after about 25 miles P0603 appeaered again. we reset code but it comes back aftershort trip. i have cleaned and reseated cables and connectors all the way to the ECM, but code comes back.