Author Topic: PO420 catalyst efficiency below threshold  (Read 1260 times)

Offline jamiesgolf

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PO420 catalyst efficiency below threshold
« on: 27 July 2014, 13:54 »
Hi all,

I have a 2.0l 8v golf which used to have a misfire. It also had this error code PO420 and had an exhaust rattle. I changed the front pipe, and noticed there was still a rattle in the middle silencer but didn't really think anything of it. The engine light went off and now a week on it has returned with the code PO420 once again. Surely I can't have knackered another catalytic converter that quickly? Doesn't seem like the lambda sensors are knackered as they picked up the problem and have registered it again but I guess they could be?

Any ideas? Thanks in advance