Howdy Folks,
I saw post another about Seafoam curing a problem, so I thought I'd post my experience where Seafoam caused a P0420 check.
I got an 04 Buick (less able) with only 40K miles on it, and I thought there might be some condensation build up in the tank over the years, so I dumped a can of Seafoam in just before filling up. Everything was fine until I got down to about 3/8 tank, then the MIL popped on while idling at a stoplight after about 30 minutes of driving. It was P0420, I cleared it and restarted the car and the light stayed off. Next trip though, again after about 30 minutes, MIL came back on while idling at a stoplight, another P0420. Then the factory original Delco battery began to fail, so when I swapped it out, that cleared the code again. By then I needed gas so I filled up, and the P0420 has yet to return, 2 tanks later.
The only thing I can think of is that there really was a lot of water in the tank for the Seafoam to soak up, and toward the end of the tank, I was pushing a lot of water through the combustion chamber and exhaust. Next time I fill up, I'm thinking about putting in another can, just to see if it happens again.
I saw post another about Seafoam curing a problem, so I thought I'd post my experience where Seafoam caused a P0420 check.
I got an 04 Buick (less able) with only 40K miles on it, and I thought there might be some condensation build up in the tank over the years, so I dumped a can of Seafoam in just before filling up. Everything was fine until I got down to about 3/8 tank, then the MIL popped on while idling at a stoplight after about 30 minutes of driving. It was P0420, I cleared it and restarted the car and the light stayed off. Next trip though, again after about 30 minutes, MIL came back on while idling at a stoplight, another P0420. Then the factory original Delco battery began to fail, so when I swapped it out, that cleared the code again. By then I needed gas so I filled up, and the P0420 has yet to return, 2 tanks later.
The only thing I can think of is that there really was a lot of water in the tank for the Seafoam to soak up, and toward the end of the tank, I was pushing a lot of water through the combustion chamber and exhaust. Next time I fill up, I'm thinking about putting in another can, just to see if it happens again.