My wife and I just started our vacation, driving towards Boston. We were driving my 2000 Honda Civic with around 188,000 miles on it. This was the beginning of a trip that would take us close to 2000 miles of driving. Shortly into the drive, my Check Engine light came on. It has NEVER come on before. Even when I blew a head gasket, it didn’t come on. Fortunately I have a ScanGauge II installed, and was able to look up the code. It was “P0420”. But knowing the code didn’t help much, I didn’t know what it meant. I pulled off at the next rest area, and pulled out my laptop computer. Thankfully, all the rest areas on the thruway have free wifi. So I looked up the code, and found it meant “Catalyst System Efficiency Below Threshold (Bank 1)”. What the heck does that mean. I did more research and found it could either be a bad catalytic converter, or a bad O2 sensor. I knew a catalytic converter could be expensive. But the problem didn’t sound like an emergency. Hopefully it was an O2 sensor. I cleared the code, and we got back onto the road. The check engine light came on again. Again I cleared it. We continued driving towards Boston, eventually stopping for gas. I filled the tank, got lunch, and got back on the road. I expected the light to come on again, but it didn’t. We kept driving. Later when I had some time, I started researching how to replace an O2 sensor. It didn’t look too difficult, but not something that I wanted to do on a road trip. But in the close to 2000 miles I have driven since then, the light has not come on. This leads me to believe that there is another cause for this check engine light.

1. Maybe some carbon got stuck in the O2 sensor when I Seafoam’ed my engine. But I had driven the car for a while after using the Seafoam. And then it suddenly got cleared out when I got fresh gas?
2. Maybe some water got into an electrical connection when I cleaned my engine? Again, I had driven the car after cleaning the engine. And I would think any residual water would have dried by then.
3. Maybe I got bad gas. This is what I am thinking. I had filled the gas tank shortly before we began the trip. And the problem went away after getting fresh gas.

When filling the tank afterwards, I tended to buy better quality gas, going to Exxon and Mobil stations, instead of the cheapest stations. Maybe that helped clean stuff out. So meanwhile, I am keeping an eye on it.

Posted by Rob in My Car on April 28th, 2011 | No Comments