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  1. Problems, Maintenance, and Warranty
    I replaced the OEM exhaust manifold in my 2009 Forester with an Eastern Catalytic Manifold from Rock Auto. Had the install verified by my mechanic. After about 200 miles the P420 code came back on. Mechanic states that the rear O2 sensor reads all over the place while running, 100mV - 1000mV...