p0420 catalyst system efficiency below threshold

[nikhsub1]

Anyone with this error? "p0420 catalyst system efficiency below threshold" This is now the 2nd time I've cleared it - new cats needed already? Truck has 7300 miles on it...

 

[802Avalanche]

Stock exhaust?

 

[1roadking]

Must be a bad batch as your the 2nd person I’ve seen with this problem in the last 2 weeks

 

[nikhsub1]

Stock exhaust?

yes.

 

[nikhsub1]

bumping this - I have SPD cats for the last year and a half, getting this code AGAIN. Must be bad 02 sensors? Bank 1 is passenger? @FordTechOne help!

 

[FordTechOne]

bumping this - I have SPD cats for the last year and a half, getting this code AGAIN. Must be bad 02 sensors? Bank 1 is passenger? @FordTechOne help!

Cat efficiency DTCs are not typically the result of a sensor issue; the condition is calculated, not directly measured. Meaning a skewed/faulty sensor reading will typically set a DTC well before the catalyst monitor is able to run. Common causes for cat efficiency DTCs include exhaust leaks, poor quality/contaminated fuel, and aftermarket engine modifications.

 

[nikhsub1]

Hmmm i only use premium top tier fuel. Could an intake and intercooler cause it?

 

[1BAD454SSv2]

I would get that code on my GEN 1 when ever i filled up with Shell premium gas . I could time the light pretty much 15 min after fill up till it turned on . After a few hundred miles it would turn off on its own. Chevron or QT gas it never happens. I believe this is one of the few codes that does not put truck into limp mode or alter performance .

 

[FordTechOne]

Hmmm i only use premium top tier fuel. Could an intake and intercooler cause it?

Not likely. Here’s the list of possible causes to consider:

• Damaged heated oxygen sensor (HO2S)
• Exhaust leaks
• Damaged exhaust manifold
• Damaged catalytic converter
• Oil contamination
• Cylinder misfiring
• Downstream HO2S wires incorrectly connected
• Damaged exhaust system pipe
• Damaged muffler and tailpipe assembly
• Leaking fuel injector
• Oil contamination of the catalyst
• Damaged turbocharger
• Base engine concerns