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Discussion Starter · #1 ·
having the po420 code intermittantly on my truck.
upper o2 sensor was replaced shortly after i got the truck this summer.
after the upper o2 sensor was replaced i got a po 420 within a couple of days.I then replaced the lower o2 sensor, on reccomendation from a mechanic. Doing this cleared up the problem for a few months.
Recently the check engine light comes on at about half a tank of fuel, but wil go away within a couple of minutes after filling up the truck.
last time i had the light on i just added 30 liters of gas , and the light cleared, even though the tank was not full and did not come on again.

am I crazy to be thinking that my gas tank observations are more than just coincedence(sp)?

Truck is a 2003 silverado, 5.3 auto.
I am pretty good about maintenence
215,000 kms
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