P0420 and P0430 codes?

[5.0]

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1997 5.0

I don't recall ever seeing a check engine light, but when I checked with my ScanGauge it said I have 2 codes - P0420 and P0430.

What could cause this, and where do I start?



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[Turdle]

does the check engine light appear when you switch the key on?

These codes "might" have been induced from filling the tank with the engine running-
Reset the PCM and see if they come back.

 

[m4dc0w]

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

P0430 Catalyst System Efficiency Below Threshold (Bank 2)

 

[5.0]

I never thought to confirm that the CEL comes on with the key... so, I just went outside and checked and no, the CEL does not come on with the key. I cleared the codes a couple days ago and they still haven't returned.

 

[Ulysses Abotisum]

does the check engine light appear when you switch the key on?

These codes "might" have been induced from filling the tank with the engine running-
Reset the PCM and see if they come back.

Yes the check engine light is on