i got a check engine light and when i checked the code im getting P0420 catalyst system efficiency below threshold (bank 1) what does that mean exactly? im thinking a bad oxygen sensor. any help is appreciated thanks

 

i only got that code when i took my cats off........

but bought tuner turned rear 02s of no problem since

 

well i have a catted xpipe on the car and have been running it about a year and never got a code.

 

Bad cat. Take it to an exhaust shop they can check it.

 

wouldnt bank 1 be before the cat?

 

Bank refers to what side. But since it is a catalist code it means your cat is bad.

 

This is what my ford service manual says.





P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Indicates the bank 1 catalyst system efficiency is below the acceptable threshold.[*]Use of leaded fuel.[*]Damaged HO2S.[*]Malfunctioning engine coolant temperature sensor.[*]High Fuel Pressure.[*]Damaged exhaust manifold.[*]Damaged catalytic converter.[*]Oil contamination.[*]Cylinder misfiring.[*]Downstream HO2S wires improperly connected.[*]Damaged exhaust system pipe.[*]Damaged muffler/tailpipe assembly.[*]Retarded spark timing.
[ul][/ul]
Compare HO2S upstream HO2S11 and downstream HO2S12 switch rate and amplitude. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S very slow and reduces the amplitude of those switches as compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of the upstream HO2S. Once beyond an acceptable limit the DTC is set.

Which means cat is bad in laymens terms.