Rep Power: 0

My wife’s got a 03 Civic that turned on the check engine light the other day when we were driving through town. I immediately got the codes read at Autozone and it came up with two codes: P0420, and P1457. Everything I’ve read online say to get a new Cat and fix the Evap leak, but my question is this…. Isn’t it odd that both these things would go wrong at the exact same time? It seems like it’s more than just a coincidence that both the CAT and the EVAP system would fail together at the same time.

The car just turned 100,000 miles the other day, and it’s been a great car, but a CAT going bad already? My trucks has got 175,000 and my Subaru has got 232,000 miles and both of them have their original Catalytic converters… The car does not have any egg smell or any bad smell of any sort that a bad Cat can have.

Is there something else that could be throwing this combination of codes? I called our closest Honda dealer for any tips, but they were no help at all, and they simply just kept telling me that “you can’t trust those codes from Autozone” and that I need to bring the car in for a true Honda diagnostic test.

I’d rather fix it myself because I’m out of work and money is tight, so any help or other ideas on what else could be wrong would be greatly appreciated.

 
Rep Power: 812

P1457 EVAP Emission Control System Leak Detected (Control Canister System)

usually caused by overfilling the gas tank past the stop point and flooding the canister. may just need a new charcoal canister. evap leaks are tricky because the system is huge and a leak could be coming from almost anywhere in the lines or valves.

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

this does NOT mean your cat is bad. it just means that your ecu thinks the cat is bad. possibly from a bad secondary oxygen sensor (which happens to be located inside the cat). try changing the sensor first, which at 100k miles you are way overdue. mine went out at 80k. if that doesnt work, there may be a problem with the actual cat like clogging or some of the catalyst fell out.

 
Rep Power: 0

Thanks for the response,

I’m still really suspicion of the timing of both codes. It seems odd that the car would have two issues like that at the exact same time. Is there any way both these codes are related? Or is it just like everything else… when it rains it pours!

 
Rep Power: 812

its possible, so always do the cheaper one first. maybe fixing the evap leak will solve the other problem.

 
Rep Power: 0

I thought I’d update everyone who may be having this same problem. Well, I got the check engine light to go away, and luckily without spending a dime! My wife and I top-off the gas tank, I know, I know, before everyone yells at me, I know everyone says to not top-off the tank, but I’ve never had a problem... until now. We stopped topping-off the tank and the check engine light went away.

I’ve had plenty of cars, and I’ve never had one that was so sensitive to topping off the tank. My Subaru has got 232,000 miles on it and it’s never had a problem. Infact, I “need” to top-off the tank in the Subaru or else the pump shuts off at half a tank.

Well, it’s been almost 2 months now, and the check engine light has been off. Fingers crossed it stays off for a while longer. I learned my lesson with the Civic, and we won’t be topping off the tank in that car anymore.

 
Rep Power: 812

you were prolly flooding the charcoal canister doing that. hopefully there isnt permanent damage. if it comes on again, id say you need to replace the canister.