Rep Power: 0

Hi All,

My fiancee has a 2001 Civic Lx (116K miles) and has the P0420 cat or 02 sensor check engine light on and has emissions testing coming up. Car drives great as far as I can tell. I am fairly certain both her 02 sensors and her cat are all original, but have no idea how to test them or tell which parts may be bad.

I got a few cans of Seafoam and a few cans of CRC 05063 Guaranteed to Pass Emissions Test Formula after reading some reviews and figuring it would clean up her system a bit and maybe the light would go off briefly enough to make it through or solve the issue entirely.

Even if it doesn't quite solve the original problem of the CEL I have been trying to do the Seafoam in the brake booster vac hose treatment and for the life of me I can't see how to get any of the hoses off. Her brake booster is 4-5in under the windshield a bit at the top of the hood and it took me a good 20min just to slide the metal hose crimp thing off. After yanking and examining the hose itself connected on the metal nozzle part, it seems impossibly tight and almost fused onto the metal - I guess because no one has touched it in 11 years...and I don't know how anyone would ever get it off...

I have been googling various other places to administer the Seafoam into the manifold that may have easy accessibility and have read that the PCV valve and the throttle body might be two other potential access points?

However, I have no idea where these may be located. I read that the PCV valve might be even harder and I might have to get under the car? I can't find anything that looks like the copper metal head of the throttle body hose that I have found on googled pictures of other civic generations under her hood.

Can anyone provide advice on another way to get the Seafoam into her manifold? Can I use the giant hose directly off of the air filter? Where is the throttle body? Any other hoses or ways to easily inject it in? I have pictures to reference to illustrate my confusion and hopefully someone can point me to something in these pictures that I can use since I am car illiterate.

Also, besides this "cleaning" I am hoping I can get an 02 sensor online and install it and see if that clears it up. At least the sensor that faces upward seems to be easily accessible from the top. It seems like an easy installation for at least this top sensor (just unscrew the old one from the cat converter shown in PIC 3, unclip it from the head, and then screw in the new one and clip it back on?)

The Below attachments are labeled PIC1, PIC2, PIC3 and PIC4. Please Help!

 
Rep Power: 257

it means your cat is gone or the secondary oxygen sensor but probably the cat so using seafoam is not going to do anything regarding the cell light. either replace the cat or use a o2 simulator to get the cell off so you can pass emissions thats what i use and pass every time. this is what i speak of http://www.robearracing.com/pd-megan...or-cel-fix.cfm

 
Rep Power: 518

Needs a cat.

If you are struggling with connectors, you might want to just leave the entire job to the pros.
HINT: There is a lock tab that must be released to get the connectors off of the metal bracket.
There is another tab to separate the connector halves.

 
Rep Power: 294

Clear the CEL. Like lowlife said, I'd pick up an O2 simulator and install it. Forget about the Seafoam. Chances are your Cat is good, you'll definitely know if/when it goes bad. I had various secondary O2 faults for years before I installed a CEL eliminator. 99.9 percent of the time they are erroneous. Get a smog check and let the station tell you that you have a bad cat. You can't buy/replace OEM cat in CA, unless you fail test or have it verified bad, anyways. Good luck.

 
Rep Power: 0

Awesome thanks for your help guys. Any chance a bad rear 02 sensor could throw this fault or would that be a different code? I.e. if the sensor itself is bad and I install this simulator I would think the readings would still be crap and I would be stuck with the same problem.

Also, I know I have to get under the car to get to the rear 02 sensor. Is it in a difficult place with little clearance as far as removing it? My biggest problem with these DIY things is that I have to remove 5 other brackets, hoses, plastic guards, etc. to get to what to the piece I want and I can't figure out how to do it...

I also have heard people recommend the 02 sensor socket? Does this help with leverage or for twisting in tight spaces? The front O2 loosened easily with just a wrench after a few seconds, so if the rear is in an open area, I would think a wrench would suffice again...

Thanks again!

 
Rep Power: 0

In my 2002 Civic EX, the CEL P0420 comes on after driving 60-70 MPH in the freeway right after I filled up the fuel tank. I know it's not the catalytic converter since I just changed it last year. I simply bought a new fuel cap (Stant 10834) at eBay for about $10 with free shipping and replaced it. Since then, no more CEL coming on.

 
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If P0420 is the only code then your issue is not the sensor. If it were the sensor you would be throwing a heat circuit code, low voltage, high voltage codes. I am dealing with the same code myself AFTER using the seafoam crap and trying to burn it all out of the system for about 2k miles now. A o2 sensor socket is a must. It will be tough to brake loose. Use a long 1/2 drive if possible. The secondary o2 must read a reading separate from the first to signal the cat "working".

I hooked up a friends solus scan tool and took a look at the voltage graphs between the two. My secondary is reading high low high low whereas it should be constant. The defouler trick being previously stated will work.

 
Rep Power: 0

I would try first changing the 02 sensors before condemning the catalytic converter. The reason the p0420 code comes on is because the ECU senses similar voltages from the front and rear o2 sensors.