The sectional pass mark is the whole story
JLPT reading is scored 0–60 — exactly one third of the total — and carries a sectional minimum you must clear on top of the overall pass mark. One section below its minimum is a fail no matter how high your total. So a candidate with excellent grammar and weak reading does not scrape through on points; they fail. This is structurally different from exams where a strong total covers a weak part.
Reading is never timed separately: it shares a booklet with Language Knowledge (Grammar), and there is no official per-item time allocation. That means your own pacing decision — how long to spend on grammar before moving to the passages — is part of the exam. Candidates who work the grammar exhaustively and then meet the long passage with eight minutes left lose the section, not the grammar.