I have a 2006 Accord 4cyl w/ AT. I live in California and believe that it is a PZEV car.
The car has 130,000 and is well maintained. Today the "check engine" light came on.
I pulled the code when I got home and got the following.

P0420
Catalyst system efficiency below threshold Bank 1

sensor readings that were stored (not a live read)

O2 Bank 1 Sensor 1
$86 $8D $8E $8F
MOD $09 $09 $09 $09
MEAS 87 128 25 27
MIN 71 96 0 0
MAX 115 225 40 50

O2 Bank 1 Sensor 2

$38 $47 $48 $49
MOD $09 $09 $09 $09
MEAS .04 .295 .885 .115
MIN .00 .290 .650 .0
MAX .20 1.27 1.275 .290

From these readings can you tell if it is a O2 sensor and if so which one? Or does this look like the CAT?

Thanks as always for your help.
Mark

 

This code means the rear (Sensor 2 ) O2 sensor is detecting a voltage pattern that indicates the catalytic converter is not working correctly. It can be caused by several things; exhaust leak ahead of converter allowing air to be pulled in, Sensor 1 subpar performance leading to poor converter efficiency, or sensor 2 fault. O2 sensor faults (1 or 2) are unlikely since you don't have any O2 sensor fault codes.

Check exhaust manifold, connections, and exhaust pipe ahead of converter for cracks or damage.

Check catalytic converter for obvious damage such as dented or loose material inside (shake the converter and listen).

You may want to have a professional shop monitor the rear o2 voltage output and see if numerous hi/lo voltages are seen indicating the converter is not performing.

Fix is likely a replacement catalytic converter. OEM is typically very expensive. There are a few aftermarket converters available (Check Eastern and DEC). They are still pretty expensive, so professional help may be indicated to be sure the problem is correctly diagnosed.

good luck

 

Beginning in about 1998 or so, I've heard that the ECU has gotten pretty good at telling the difference between a bad converter vs. bad O2 sensors. So like Tex says, the lack of O2 sensor errors makes it seem like the converter is bad. Still, in most cases the first step in diagnosing is to reset the ECU (erase codes) then see whether it comes back.

Certainly look for (and FIX) any exhaust leaks. The O2 sensors operate by measuring the DIFFERENCE in O2 from outside to inside. So if there's exhaust or oil or antifreeze blowing onto the OUTSIDE of the sensor, that will throw it off. Some stuff can cause permanent damage to the sensor, but that should result in a sensor error code.

 

Thanks for the replys. Pretty much what I thought.
I have already checked for exhust leaks - NONE. There is nothing leaking or blowing onto the CAT or O2 sensors. The CAT looks like it is in ggod shape, no obvious damage.

After reading this I looked through the warranty manual and found that CA emissions could be warrantied at 36,000 - 80,000 or 150,000 miles.

I "think" this repair may fall under warranty. Even though I have 130,000 miles. PZEV partial zero emission) vehicles have smog component warranties of 15 years / 150,000 miles and I believe this car is classified as PZEV. I called the dealer and they told me that I was out of warranty. They said the only PZEV vehicles are hybrid. However I called Honda customer care and they stated that my car IS a PZEV car (since it has an auto trans) therefore it is under warranty. So I guess this is where the fight starts.
Hopefully I can save major $$$$ and get this covered under warranty.

Mark

 

I thought that only hybrids are PZEV.
But I'd still call Honda customer care, & ask them to tell the dealer that YES IT IS covered...

 

That is what the service writter said.
Just heard back from the dealer. After looking at the information that I sent and discussing it with his manager, they agreed and are covering the repair.
Good thing since the CAT is $900 plus not including labor.

This is off the owners link website.


Engineering
Engine Type: In-Line 4-Cylinder
Engine Block/Cylinder Head: Aluminum-Alloy
Displacement (cc): 2354
Horsepower @ rpm (SAE net, Rev 8/04)*: 166 @ 5800
Torque (lb.-ft. @ rpm): 160 @ 4000
Bore and Stroke (mm): 87.0 x 99.0
Compression Ratio: 9.7 : 1
Redline: 6500
Valve Train: 16-Valve DOHC i-VTEC®
Multi-Point Fuel Injection
Drive-by-Wire Throttle System™
CARB Emissions Rating: LEV-2/PZEV**
Direct Ignition System with Immobilizer
100,000-Miles-or-More Tune-Up Interval***


** AT models are PZEV-rated in California and certain northeastern states.




Thanks to everyone for the help!!
Mark