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Dan, Technician
Category: Car
Satisfied Customers: 24579
Experience:  Independent Shop Experience, 2 Year Automotive Diploma, & Access to Information Database
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Engine Mgt line has come on. Giving fault codes P0420 & P0430. Bank1/2

Customer Question

Engine Mgt line has come on. Giving fault codes P0420 & P0430.
'Bank1/2 cat convertor efficiency below threshold'.

Surely both cats wont have failed at the same time, too much of a coincidence?
Been advised that it is probably the O2 sensors at fault, however both faulting at the same time seems a bit odd.
(XTYpe 2.0 2002)
Submitted: 4 years ago.
Category: Car
Expert:  Dan replied 4 years ago.
Welcome to JustAnswer, my name is Dan and I'm here to help get your problem resolved. If the oxygen sensors were the problem that would mean 2 sensors would need to fail at the same time also which is unlikely. These codes mean catalytic converters fail a lot more often then oxygen sensors but things to check first would be a exhaust leak and large vacuum leaks. If no vacuum leaks or exhaust leaks are found you may just be setting false codes which would require the computer to be re-flashed at the dealership, this is where I would start if there are no vacuum leaks or exhaust leaks. Let me know if you have questions or if there is anything else I can do to help. Thanks.