code PO420 cat inefficient Bank 1

Question

trying to resolve check engine light being on.  Code PO420 comes up with Catalytic converter inefficient Bank 1

Answer 1

Hi Bob,

Hate to say it but usually the problem with this code is actually a bad converter. This is the first converter on the back of the engine right off the exhaust manifold. You can remove the front pipe and check to see if the converter is broken up inside. Also, sometimes this code will appear on these if any of the bolts for the exhaust shield have fallen out. This gives the rear O2 sensor a lean reading which will cause it to pop this code.