Hyundai 28510-3C660 Exhaust Manifold Catalytic Assembly, Right

Working in the engine compartment, remove the upper heat shield from the manifold. The upper oxygen sensor must be removed from 2006 and later engines in order to remove the exhaust manifold heat shield. On 2006 and later models, there is an exhaust manifold brace that must be unbolted from the manifold. Disconnect any other interfering brackets; these vary from vehicle to vehicle.

Disconnect the cable from the negative terminal of the battery.

The catalyst cannot convert harmful pollutants into harmless compounds without oxygen. It is most efficient at capturing and storing oxygen when the exhaust gases are mixed at the ideal (stoichiometric) air/fuel ratio of 14.7:1. If the air/fuel ratio is too lean or too rich for an extended period, it can affect the catalyst's ability to function properly.