I just bought a 95 accord. It was smogged(ca.) six months ago and passed. Just tried to smog it and it failed because of O2 sensor and catalytic converter. Is therre any way to fool the O2 sensor and the cat to get it passed the smog. I'm going to run premium and add injector cleaner before trying again. ( this will be the last time it has to pass smog and I don't want to buy a new cat and O2 sensor) Any other ideas ? Thanks.

 

Technically speaking, there are ways to make the signal line from the O2 sensor (narrow band type sensor) to the ECU be within expected parameters and not set a trouble code and Check Engine Light. It can be done with resistors or a combination of resistor and capacitor. -- I will not get into the illegal aspects of doing such or do I know the resistor values, etc. needed for the Accord.

Regardless, a 1995 Accord is OBD-I and only has one O2 sensor (it is before the cat, there is no secondary O2 sensor on the 95), so even if you fooled the ECU regarding the O2 sensor signal, there is no fooling the tail pipe emission test for a bad converter.

 

Well, things like oil changes, spark plugs, etc. will help lower certain emissions and possibly a few other tricks; but, probably not for a really bad cat.

 

When I was getting the code "P0420 Catalyst system efficiency below threshold"
I made an adapter to put between the o2 sensor and the catalytic. After that my light NEVER came back on for the cat.

The only difference here is that MY o2 sensor worked. Since your o2 sensor does not work I doubt it will work for you.

Did they give you a print out? With exact info pertaining why you did not pass?

If you want, email me @ jfidel.herrera@gmail.com so I can show you how to make that adapter.

 

There are differences in the emission sensors and codes between a 1998 Accord and a 1995 Accord, which throws a wrench in this. The 1995 is OBD-I, while the 1998 is OBD-II.

• The trouble codes are different. OBD-I trouble codes on the Honda are represented by numbers such as 0 - 43. OBD-II trouble codes are represented by P,B,C, or U and numbers. P being power train, where emission controls being a subsystem of the power train trouble code numbering.
• The 1995 Accord only has one O2 sensor (located before the cat). There is no rear sensor on the 1995 to measure the efficiency of the cat. The 1998 Accord has two O2 sensors, one primary sensor (if the 1998 is a ULEV, the primary (pre-cat) is an Air/Fuel ratio sensor) and a secondary O2 sensor. The rear O2 sensor is principally there to measure the efficiency of the cat.

The P0420 is Catalyst System Efficiency Below Threshold (Bank 1), which is set when the measurement of the switching activity between the primary sensor and the secondary sensor do not fall withing the expected parameters of what Honda sets for a properly working cat. (Somewhat like that.)

The P0420 code being set does not necessarily mean the cat is bad or that it actually won't meet tail pipe emissions standards. It won't pass in California if the Check Engine Light is on or a trouble code is set, whether it meet tail pipe emissions or not. Sometimes some car manufacturers set their parameters (standards) in the ECM/PCM a little too narrow. For example, on Honda Accord Hybrids and certain Toyotas, the car manufacturer had ECM/PCM software updates to the ECM/PCM related to P0420 when the cat was actually still good. There are cars where the car manufacturer did not have software updates and the cats still would actually pass a tail pipe emission test.

For either the primary O2 sensor or secondary sensor, it is technically possible to make the signal line from either O2 sensor to the ECU be within expected parameters and not set a trouble code and Check Engine Light. There are different methods, one method doesn't require a properly working sensor while the other method requires a properly working sensor. (The practice of conditioning the line signal is more prevalent with Toyotas.)

For the P0420, generally, you would be changing the signal for the rear O2 sensor. However, a 1995 Accord doesn't have a rear O2 sensor or have any trouble code even remotely close to Catalyst System Efficiency Below Threshold.

 

Thanks redbull-1 and Jfidelh. I started a new thread with information that I should have had in my original post. Thanks for your help.