I'm having the P0420 code on my SUV. I had just filled the tank when it came on, so I tightened the cap. The code cleared for about 1/4 the tank and then came back on and stayed the rest of that tank. The same thing happened again when I filled the tank to Full. What causes this problem?
Honda has a technical service bulletin (TSB) out for this condition. There are 2 possibilities to correct this fault, according to the bulletin:
One last thing to consider is the post catalytic oxygen sensor. To avoid a trip to the dealer, you may want to enlist the help of a mechanic to check the post catalytic oxygen sensor and inspect the exhaust system for leaks.
If the engine computer software has not ever been updated, then you will have to go to the dealer to correct this.