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Planning on leaving for a trip to Vermont after work but on my way to work fill up 03 Element with gas and a 3 miles later check engine light comes on. Pull over check fluids and gas cap seems tight and clicks. I can not remember if I heard a click this morning or not, attendant filled tank (NJ). Light still on finish my ride to work another three miles.

Check autozone sight remembered they do free diagnostic checks. Cruise the EOC boards here see what I can pick up. Go to autozone at lunch get a P0420 which determined cat system effeciency for bank 1 is below threshold...bla bla bla oxygen sensors monitor catylitic converters ability to store o2. Possibly from vac leak, engine misfires or engine oil leaking into exhaust guide seals, piston rings.

Question
1. Could an untight gas cap cause the vacuum problem? I stopped home really quick to get service maual and when I started up the car light was out.:grin: Should I worry about driving it up north?

Thanks

Chris
 

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p0420 is not the gas cap. Try replacing the rear 02(get it from honda) first, if you find no exhaust leaks, or air leaks.

I had the exact same code, around the same miles, I replace the cat, the light still came on, I then replaced the rear 02, fixed the problem, may have been a combination of both, but the rear 02 is the cheapest.
 

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I had that same code come up on a chevy van and the front part of the cat had fallen apart and I did use a aftermarket cat and it worked great but now here in good ole Cal you can't get those anymore.:x
 

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Per the Honda Service Manual P0420 Catalyst system efficiency below threshold, (Bank 1). Can't find what bank 1 means but I think its the second sensor (secondary heated oxygen sensor) that might be the culprit if not an actual bad cat.
 

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Bank 1 means the left exhaust bank on a V engine and since the E is a 4 cylinder there is only 1 bank. You have bank 1 sensor 1 and bank 1 sensor 2 for the oxygen sensors. When that code comes up it means that the cat is not doing its job and both sensors are reading close to the same.
 

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Bank 1 means the left exhaust bank on a V engine and since the E is a 4 cylinder there is only 1 bank. You have bank 1 sensor 1 and bank 1 sensor 2 for the oxygen sensors. When that code comes up it means that the cat is not doing its job and both sensors are reading close to the same.
Had this all too common situation in my 99 Accord around 160k miles. I never changed mine as I could always clear the code long enough to pass inspections and otherwise ignore the CE light.

Couple of things I learned from a Master Honda Tech friend on this:
- As shown in the quoted text, it confirms your cat is bad. #1 sensor takes a reading, air then goes thru cat and then to sensor #2. Computer looks for a specific range of change in readings to confirm proper cat operation. If readings are too close or the same, sends code for bad cat.
- The design on the Honda 4 cylinders exhaust has the #2 sensor between the cat and exhaust exit. THis is important since as the cat further breaks down, pieces of the internal media will break off and travel down the exhaust...and in this case, out the tailpipe. (Other designs including the Honda 6 cylinder will track the debris back into some susceptible areas of the engine.)
In other words, you're usually safe to drive until next inspection or when you're tired of seeing the CE light. Of course, I would never support openly dirving a vehicle that violates any emissions laws of your area.
- Honda is notorious for only Honda cat's providing the real fix here. Aftermarket cats just don't support the sensors behaving well.

Good news: You're not grounded right off the bat. Bad news, they just ain't cheap.
 

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disconnecting battery ground clears p0420 for up to two months?

Over the past several years, I have first replaced the foreward O2 sensor due to a P0420 CEL. A year later, I ended up replacing both O2 sensors to clear a CEL for 0420. During the last year, I have simply been lifting the ground cable from the battery for a few minutes and then replacing same to clear the CEL for p0420. This proceedure clears the problem (?) for about 6 to 8 weeks when the CEL comes back on for 0420. Yesterday, the same scenario played out yet again. I simply lifted the ground cable for about 5 sec and reconnected it again. This time, I didn't even have to reprogram my radio!
My question is how can this be possible? The computer apparently "sees" a problem and initiates a CEL. I clear the light and the "problem" is not "Detected" for another 6 to 8 weeks! In the meantime, my performance is just fine with absolutely no change. My tail pipe is white glove inspection clean after 133,000 miles. I adjusted my own valves over a year ago and that is not a factor. I passed Calif. emissions test during this time with flying colors. I seem to have a new ghost now that my gage cluster problem has been solved!
I would appreciate any thoughts on this situation which certainy seems to be easy to deal with without further "throwing parts at" solutions. If I have a real problem with my converter or sensors, why would it take so long to generate a CEL after being cleared? Thanks in advance for your help:)
 

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i'm guessing, but it may take a while for the ECU to eventually get any bad data back from the o2 sensor? in other words, the vehicle is working well, except for the 2 month fluke. i'd do what you are doing now.
 

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this code is probably your outboard oxy sensor, even though it's not bad it's reading a cat problem, got the same code on my daughters celica and the easy fix is to buy 18mm spark plug anti fowlers [about $8 bucks at advanced auto]- drill a 1/2 hole in one and screw your sensor into that and then piggy back the other and screw the whole assembly into the tailpipe, this pulls the sensor away from the gases and never triggers another code.
way cheaper than the $1000 dealer charge to fix the problem.
 

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When you changed the oxygen sensors , did you use Honda sensors ? Some others brands , don't match up and could be causing this ......
Just a thought ........

good luck
 

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I don't understand why you need to disconnect the battery to clear the code.. Doesn't your code reader clear the code for you?
 

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My scan gage II doesn't clear the code. I push the buttons, but the code does not clear. Lifting the neg cable does the job. Yes, my new sensors have all been Honda parts on line from Bernardi. My scan gage II does tell me
"no codes, not ready" after lifting the ground cable for a few seconds. It takes an unknown number starts and stops and various driving parameters to rest the computer and meet all critiorion to be "ready" In the past, this can tak up to two weeks of normal driving. I just don't see why it takes so long for the sensor code to come back:? It is five weeks, and counting, since I lifted the neg cable to clear the sensor code. Everything is fine?????
 

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P0420 is a catalytic convertor inefficiency code. With all the additives and moisture in the fuel I'm not surprised by the code.
I second the recommendations of the others of changing all the fluids and filters and run the car for a few weeks. Most of these problems will work themselves out.
 

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After almost six and a half months, my CEL came on this morning for P0420
yet again. I disconnected my battery ground cable, reconnected my battery ground cable, reset my radio this time, and CEL is cleared. Here I go again:)
 

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If I remember that is Cat below efficiency threshold. If that's true you cat might be at the failing point. It looks at the O2 difference between the 2 O2 sensors and if they are close to each other you will get a CEL. Take it up pacific island drive floored.:-D I use to live down there....
 

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Thanks Slimerdogs. Had reason to go out Alicia Parkway this morning and did indeed jump on Pacific Island Drive. Floored it with my wife as shotgun
and scooted up the hill at 60 mph which kept me with the flow of traffic.
Good test. My toaster also passed smog last april with flying colors and my exhaust pipe is white glove clean. Again, my real concern is why the computer says there is a problem, and I can lift the ground cable to clear the problem, and then not have problem show up again for months on end!:)
 

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Well ether the rear O2 sensor is acting up or the cat is having a slight failure. Resetting the computer by pulling the ground cable causes the computer to relearn.
 

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Yes, that is my interpretation of what is going on. Just don't want to buy yet another sensor or two if computor "relearns" that nothing is going on. :)
 

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Just don't buy a Bosch sensor as they are trash.
 
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