adorek24

5-manual I-4, 68,000 miles, maintenance by the book, only Shell gas, 60/40 hwy/city, mpg avg 28-32, driven "softly".

The check engine light came on yesterday during my routine drive home from work, AZ pulled the code, p0420, Catalytic system below threshold. This happened also a few months ago in January. In both cases after ~5 cold starts, regardless of mileage driven, the light went off on its own. Since this is the second time it has happened, I'm concerned about what might be going on.

I did a bit of research and found the following TSB's:


Make : HONDA Model : ACCORD Year : 2003
Manufacturer : AMERICAN HONDA MOTOR CO.
Service Bulletin Num : 604 Date of Bulletin: JUN 16, 2004
NHTSA Item Number: 10014141
Component: ENGINE AND ENGINE COOLING:ENGINE
Summary:
UPDATE ECM/PCM FOR DIAGNOSTIC TROUBLE CODE P0420, CATALYST BELOW THRESHOLD. *NM


HONDA Model : ACCORD Year : 2004
Manufacturer : HONDA (AMERICAN HONDA MOTOR CO.)
Service Bulletin Number : 07012004 Date of Bulletin : JUL 01, 2004
NHTSA Item Number : 10014032
Component : EQUIPMENT:OTHER:OWNERS/SERVICE/OTHER MANUAL
Summary :
S/M FIX DTC P0420 TROUBLESHOOTING. *EH



Not a great deal of info there, I know, especially with the second one, but I was wondering if anyone has had their ecu updated, as specified in the first TSB for code p0420? If so, did it solve the problem?

I bought a scan tool online (Equus 3130) before the engine light went off. When it arrives I hope to get more info in real time on what the issue might be, my guess from what I've read is that there is a high probability that it is the post catalytic o2 sensor, but could be the upstream one as well.

It is one thing if the check engine light stays on, but in my case it has gone on, then off, twice, and it has me scratching my head.

KWayRacing

Just have the PCM updated.

anoble1

This "PCM" is this the Powertrain Control Module? Where is it located, and how do you update? I am having the same issue but I just replaced my catalytic converter AND my lower o2 sensor. Note, it was not the OEM cat, and I replaced the o2 sensor with a new bosch sensor. My car has 155,000 miles.

KWayRacing

Dealer can update the software. Probably 50-100 bucks.

anoble1

And that is supposed to make my computer notice the new high flow cat i put on it, and the sensor? To make it read normal again?

Thanks

Ross 2.0

High flow cats are garbage and will always set a P0420. You either need to use spark plug defoulers on the secondary o2 or put the original cat back in like it should be.

To the OP just have the software updated. We've had very few cats go out on those cars.

jstasney

This can be caused by several factors.
A dirty fuel system, dirty injectors, dirty O2 sensors any of which fool the ECM/PCM into setting the wrong air/fuel mixtures which trip the O2 sensors by the wrong burnt fuel mixture passing by the pre-converter O2 sensor.
The converter can only clean up so much contaminated burnt air/fuel mixture

If it's a rich mixture, more of the rich mixture gets through the Cat than should, making the aft O2 sensor read the Air/fuel gas mixture outside the pre-set parameters.

Try running Berryman's B12 in the gas first to clean up the fuel system, O2 sensors and fuel injectors along with premium gasoline.

My short story is on a 2004 Accord w/211,000 miles is, 2 cans of B12 @ $7.50 and a half tank (8 gal) of Chevron Techron premium gasoline.
60 miles later and the light is out.

DaddyMack2698

I need to replace bank 2 sensor 2 in my 2003 accord can someone help please? Where is it at? A diagram would be great if possible..